Network Working Group F. L. Templin, Ed.
Internet-Draft The Boeing Company
Intended status: Informational 21 April 2022
Expires: 23 October 2022
Transmission of IP Packets over Overlay Multilink Network (OMNI)
Interfaces
draft-templin-6man-omni-59
Abstract
Mobile nodes (e.g., aircraft of various configurations, terrestrial
vehicles, seagoing vessels, space systems, enterprise wireless
devices, pedestrians with cell phones, etc.) communicate with
networked correspondents over multiple access network data links and
configure mobile routers to connect end user networks. A multilink
virtual interface specification is presented that enables mobile
nodes to coordinate with a network-based mobility service and/or with
other mobile node peers. The virtual interface provides an
adaptation layer service that also applies for more static
deployments such as enterprise and home networks. This document
specifies the transmission of IP packets over Overlay Multilink
Network (OMNI) Interfaces.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 23 October 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 15
4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 15
5. OMNI Interface Maximum Transmission Unit (MTU) . . . . . . . 22
5.1. Jumbograms . . . . . . . . . . . . . . . . . . . . . . . 23
5.2. IPv6 Parcels . . . . . . . . . . . . . . . . . . . . . . 24
6. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 24
6.1. OAL Source Encapsulation and Fragmentation . . . . . . . 25
6.2. OAL L2 Encapsulation and Re-Encapsulation . . . . . . . . 30
6.3. OAL L2 Decapsulation and Reassembly . . . . . . . . . . . 33
6.4. OAL Header Compression . . . . . . . . . . . . . . . . . 34
6.5. OAL-in-OAL Encapsulation . . . . . . . . . . . . . . . . 38
6.6. OAL Identification Window Maintenance . . . . . . . . . . 40
6.7. OAL Fragment Retransmission . . . . . . . . . . . . . . . 45
6.8. OAL MTU Feedback Messaging . . . . . . . . . . . . . . . 46
6.9. OAL Super-Packets . . . . . . . . . . . . . . . . . . . . 48
6.10. OAL Bubbles . . . . . . . . . . . . . . . . . . . . . . . 49
6.11. OAL Requirements . . . . . . . . . . . . . . . . . . . . 50
6.12. OAL Fragmentation Security Implications . . . . . . . . . 51
6.13. OMNI Hosts . . . . . . . . . . . . . . . . . . . . . . . 52
6.14. IP Parcels . . . . . . . . . . . . . . . . . . . . . . . 55
7. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 58
8. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 59
9. Unique-Local Addresses (ULAs) . . . . . . . . . . . . . . . . 60
10. Global Unicast Addresses (GUAs) . . . . . . . . . . . . . . . 63
11. Node Identification . . . . . . . . . . . . . . . . . . . . . 64
12. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 65
12.1. The OMNI Option . . . . . . . . . . . . . . . . . . . . 66
12.2. OMNI Sub-Options . . . . . . . . . . . . . . . . . . . . 67
12.2.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 69
12.2.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 69
12.2.3. Neighbor Coordination . . . . . . . . . . . . . . . 70
12.2.4. Interface Attributes . . . . . . . . . . . . . . . . 72
12.2.5. Multilink Forwarding Parameters . . . . . . . . . . 75
12.2.6. Traffic Selector . . . . . . . . . . . . . . . . . . 80
12.2.7. Geo Coordinates . . . . . . . . . . . . . . . . . . 81
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12.2.8. Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
Message . . . . . . . . . . . . . . . . . . . . . . . 82
12.2.9. Host Identity Protocol (HIP) Message . . . . . . . . 83
12.2.10. PIM-SM Message . . . . . . . . . . . . . . . . . . . 85
12.2.11. Fragmentation Report (FRAGREP) . . . . . . . . . . . 86
12.2.12. Node Identification . . . . . . . . . . . . . . . . 87
12.2.13. ICMPv6 Error . . . . . . . . . . . . . . . . . . . . 89
12.2.14. QUIC-TLS Message . . . . . . . . . . . . . . . . . . 90
12.2.15. Proxy/Server Departure . . . . . . . . . . . . . . . 90
12.2.16. Sub-Type Extension . . . . . . . . . . . . . . . . . 91
13. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 94
14. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 95
14.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 95
14.2. Client-Proxy/Server Loop Prevention . . . . . . . . . . 96
15. Router Discovery and Prefix Registration . . . . . . . . . . 96
15.1. Window Synchronization . . . . . . . . . . . . . . . . . 105
15.2. Router Discovery in IP Multihop and IPv4-Only
Networks . . . . . . . . . . . . . . . . . . . . . . . . 106
15.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 108
15.4. OMNI Link Extension . . . . . . . . . . . . . . . . . . 110
16. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 111
17. Proxy/Server Resilience . . . . . . . . . . . . . . . . . . . 111
18. Detecting and Responding to Proxy/Server Failures . . . . . . 111
19. Transition Considerations . . . . . . . . . . . . . . . . . . 112
20. OMNI Interfaces on Open Internetworks . . . . . . . . . . . . 113
21. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 115
22. (H)HITs and Temporary ULA (TMP-ULA)s . . . . . . . . . . . . 116
23. Address Selection . . . . . . . . . . . . . . . . . . . . . . 117
24. Error Messages . . . . . . . . . . . . . . . . . . . . . . . 118
25. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 118
25.1. "Protocol Numbers" Registry . . . . . . . . . . . . . . 118
25.2. "IEEE 802 Numbers" Registry . . . . . . . . . . . . . . 118
25.3. "IPv4 Special-Purpose Address" Registry . . . . . . . . 118
25.4. "IPv6 Neighbor Discovery Option Formats" Registry . . . 119
25.5. "Ethernet Numbers" Registry . . . . . . . . . . . . . . 119
25.6. "ICMPv6 Code Fields: Type 2 - Packet Too Big"
Registry . . . . . . . . . . . . . . . . . . . . . . . 119
25.7. "OMNI Option Sub-Type Values" (New Registry) . . . . . . 119
25.8. "OMNI Geo Coordinates Type Values" (New Registry) . . . 120
25.9. "OMNI Node Identification ID-Type Values" (New
Registry) . . . . . . . . . . . . . . . . . . . . . . . 120
25.10. "OMNI Option Sub-Type Extension Values" (New
Registry) . . . . . . . . . . . . . . . . . . . . . . . 121
25.11. "OMNI RFC4380 UDP/IP Header Option" (New Registry) . . . 121
25.12. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry) . . 122
25.13. Additional Considerations . . . . . . . . . . . . . . . 122
26. Security Considerations . . . . . . . . . . . . . . . . . . . 123
27. Implementation Status . . . . . . . . . . . . . . . . . . . . 124
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28. Document Updates . . . . . . . . . . . . . . . . . . . . . . 124
29. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 124
30. References . . . . . . . . . . . . . . . . . . . . . . . . . 126
30.1. Normative References . . . . . . . . . . . . . . . . . . 126
30.2. Informative References . . . . . . . . . . . . . . . . . 128
Appendix A. OAL Checksum Algorithm . . . . . . . . . . . . . . . 137
Appendix B. IPv6 ND Message Authentication and Integrity . . . . 137
Appendix C. VDL Mode 2 Considerations . . . . . . . . . . . . . 138
Appendix D. Client-Proxy/Server Isolation Through Link-Layer
Address Mapping . . . . . . . . . . . . . . . . . . . . . 139
Appendix E. Change Log . . . . . . . . . . . . . . . . . . . . . 140
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 140
1. Introduction
Mobile nodes (e.g., aircraft of various configurations, terrestrial
vehicles, seagoing vessels, space systems, enterprise wireless
devices, pedestrians with cellphones, etc.) configure mobile routers
with multiple interface connections to wireless and/or wired-line
data links. These data links may have diverse performance, cost and
availability properties that can change dynamically according to
mobility patterns, flight phases, proximity to infrastructure, etc.
The mobile router acts as a Client of a network-based Mobility
Service (MS) by configuring a virtual interface over its underlay
interface data link connections to support the "6M's of modern
Internetworking" (see below).
Each Client configures a virtual interface (termed the "Overlay
Multilink Network Interface (OMNI)") as a thin layer over its
underlay network interfaces (which may themselves connect to virtual
or physical links). The OMNI interface is therefore the only
interface abstraction exposed to the IP layer and behaves according
to the Non-Broadcast, Multiple Access (NBMA) interface principle,
while underlay interfaces appear as link layer communication channels
in the architecture. The OMNI interface internally employs the "OMNI
Adaptation Layer (OAL)" to ensure that original IP packets are
adapted to diverse underlay interfaces with heterogeneous properties.
The OMNI interface connects to a virtual overlay known as the "OMNI
link". The OMNI link multinet service spans one or more
Internetworks that may include private-use infrastructures (e.g.,
enterprise networks) and/or the global public Internet itself.
Client OMNI interfaces interact with the MS and/or other OMNI nodes
through IPv6 Neighbor Discovery (ND) control message exchanges
[RFC4861]. The MS consists of a distributed set of service nodes
(including Proxy/Servers and other infrastructure elements) that also
configure OMNI interfaces. Automatic Extended Route Optimization
(AERO) in particular provides a companion MS compatible with the OMNI
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architecture [I-D.templin-6man-aero]. AERO discusses details of ND
message based route optimization, mobility management, and multinet
traversal while the fundamental aspects of OMNI link operation are
discussed in this document.
Each OMNI interface provides a multilink nexus for exchanging inbound
and outbound traffic via selected underlay interface(s). The IP
layer sees the OMNI interface as a point of connection to the OMNI
link. Each OMNI link has one or more associated Mobility Service
Prefixes (MSPs), which are typically IP Global Unicast Address (GUA)
prefixes assigned to the link and from which Mobile Network Prefixes
(MNPs) are derived. If there are multiple OMNI links, the IP layer
will see multiple OMNI interfaces.
Each Client receives an MNP through IPv6 ND control message exchanges
with Proxy/Servers over Access Networks (ANETs) and/or open
Internetworks (INETs). The Client sub-delegates the MNP to
downstream-attached End-user Networks (ENETs) independently of the
underlay interfaces selected for data transport. The Client acts as
a fixed or mobile router on behalf of peers on its ENETs, and uses
OMNI interface control messaging to coordinate with Hosts, Proxy/
Servers and/or other Clients. The Client iterates its control
messaging over each of the OMNI interface's ANET/INET underlay
interfaces in order to register each interface with the MS (see
Section 15). The Client can also provide Proxy/Server-like services
for a recursively nested chain of other Clients located in
downstream-attached ENETs.
Clients may connect to multiple distinct OMNI links within the same
OMNI domain by configuring multiple OMNI interfaces, e.g., omni0,
omni1, omni2, etc. Each OMNI interface is configured over a set of
underlay interfaces and provides a nexus for Safety-Based Multilink
(SBM) operation. The IP layer applies SBM routing to select a
specific OMNI interface, then the selected OMNI interface applies
Performance-Based Multilink (PBM) internally to select appropriate
underlay interfaces. Applications select SBM topologies based on IP
layer Segment Routing [RFC8402], while each OMNI interface
orchestrates PBM internally based on OMNI layer Segment Routing.
OMNI provides a link model suitable for a wide range of use cases.
For example, the International Civil Aviation Organization (ICAO)
Working Group-I Mobility Subgroup is developing a future Aeronautical
Telecommunications Network with Internet Protocol Services (ATN/IPS)
and has issued a liaison statement requesting IETF adoption [ATN] in
support of ICAO Document 9896 [ATN-IPS]. The IETF IP Wireless Access
in Vehicular Environments (ipwave) working group has further included
problem statement and use case analysis for OMNI in a document now in
AD evaluation for RFC publication
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[I-D.ietf-ipwave-vehicular-networking]. Still other communities of
interest include AEEC, RTCA Special Committee 228 (SC-228) and NASA
programs that examine commercial aviation, Urban Air Mobility (UAM)
and Unmanned Air Systems (UAS). Pedestrians with handheld devices
represent another large class of potential OMNI users.
OMNI supports the "6M's of modern Internetworking" including:
1. Multilink - a Client's ability to coordinate multiple diverse
underlay interfaces as a single logical unit (i.e., the OMNI
interface) to achieve the required communications performance and
reliability objectives.
2. Multinet - the ability to span the OMNI link over a segment
routing topology with multiple diverse administrative domain
network segments while maintaining seamless end-to-end
communications between mobile Clients and correspondents such as
air traffic controllers, fleet administrators, etc.
3. Mobility - a Client's ability to change network points of
attachment (e.g., moving between wireless base stations) which
may result in an underlay interface address change, but without
disruptions to ongoing communication sessions with peers over the
OMNI link.
4. Multicast - the ability to send a single network transmission
that reaches multiple Clients belonging to the same interest
group, but without disturbing other Clients not subscribed to the
interest group.
5. Multihop - a mobile Client vehicle-to-vehicle relaying capability
useful when multiple forwarding hops between vehicles may be
necessary to "reach back" to an infrastructure access point
connection to the OMNI link.
6. MTU assurance - the ability to deliver packets of various robust
sizes between peers without loss due to a link size restriction,
and to dynamically adjust packets sizes to achieve the optimal
performance for each independent traffic flow.
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This document specifies the transmission of IP packets and control
messages over OMNI interfaces. The operation of both IP protocol
versions (i.e., IPv4 [RFC0791] and IPv6 [RFC8200]) is specified as
the network layer data plane, while OMNI interfaces use IPv6 ND
messaging in the control plane independently of the data plane
protocol(s). OMNI interfaces also provide an OAL based on
encapsulation and fragmentation over heterogeneous underlay
interfaces as an adaptation sublayer between L3 and L2. Both OMNI
and the OAL are specified in detail throughout the remainder of this
document.
2. Terminology
The terminology in the normative references applies; especially, the
terms "link" and "interface" are the same as defined in the IPv6
[RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications.
Additionally, this document assumes the following IPv6 ND message
types: Router Solicitation (RS), Router Advertisement (RA), Neighbor
Solicitation (NS), Neighbor Advertisement (NA) and Redirect. Hosts,
Clients and Proxy/Servers that implement IPv6 ND maintain per-
neighbor state in Neighbor Cache Entries (NCEs). Each NCE is indexed
by the neighbor's network layer address(es) while the neighbor's OAL
encapsulation address provides context for Identification
verification.
The Protocol Constants defined in Section 10 of [RFC4861] are used in
their same format and meaning in this document. The terms "All-
Routers multicast", "All-Nodes multicast" and "Subnet-Router anycast"
are the same as defined in [RFC4291] (with Link-Local scope assumed).
The term "IP" is used to refer collectively to either Internet
Protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) when a
specification at the layer in question applies equally to either
version.
The following terms are defined within the scope of this document:
L2
The Data Link layer in the OSI network model. Also known as
"layer-2", "link-layer", "sub-IP layer", etc.
L3
The Network layer in the OSI network model. Also known as "layer-
3", "IP layer", etc.
Adaptation layer
A mid-layer that adapts L3 to a diverse collection of L2 underlay
interfaces and their encapsulations. (No layer number is
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assigned, since numbering was an artifact of the legacy reference
model that need not carry forward in the modern architecture.)
The adaptation layer sees the upper layer as "L3" and sees all
lower layer encapsulations as "L2 encapsulations", which may
include UDP, IP and true link-layer (e.g., Ethernet, etc.)
headers.
Access Network (ANET)
a connected network region (e.g., an aviation radio access
network, satellite service provider network, cellular operator
network, WiFi network, etc.) that connects Clients to the Mobility
Service. Physical and/or data link level security is assumed, and
sometimes referred to as "protected spectrum". Private enterprise
networks and ground domain aviation service networks may provide
multiple secured IP hops between the Client's point of connection
and the nearest Proxy/Server.
Internetwork (INET)
a connected network region with a coherent IP addressing plan that
provides transit forwarding services between ANETs and/or OMNI
nodes that coordinate with the Mobility Service over unprotected
media. Since physical and/or data link level security cannot
always be assumed, security must be applied by upper layers if
necessary. The global public Internet itself is an example.
End-user Network (ENET)
a simple or complex "downstream" network that travels with the
Client as a single logical unit. The ENET could be as simple as a
single link connecting a single Host, or as complex as a large
network with many links, routers, bridges and Hosts. The ENET
could also provide an "upstream" link in a recursively-descending
chain of additional Clients and ENETs. In this way, an ENET of an
upstream Client is seen as the ANET of a downstream Client.
{A,I,E}NET interface
a Client's attachment to a link in an {A,I,E}NET.
*NET
a "wildcard" term used when a given specification applies equally
to both ANET/INET cases. From the Client's perspective, *NET
interfaces are "upstream" interfaces that connect the Client to
the Mobility Service, while ENET interfaces are "downstream"
interfaces that the Client uses to connect downstream ENETs, Hosts
and/or other Clients.
underlay interface
an ANET/INET/ENET interface over which an OMNI interface is
configured. The OMNI interface is seen as a L3 interface by the
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IP layer, and each underlay interface is seen as a L2 interface by
the OMNI interface. The underlay interface either connects
directly to the physical communications media or coordinates with
another node where the physical media is hosted.
OMNI link
a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured
over one or more INETs and their connected ANETs/ENETs. An OMNI
link may comprise multiple distinct "segments" joined by L2
forwarding devices the same as for any link; the addressing plans
in each segment may be mutually exclusive and managed by different
administrative entities. Proxy/Servers and other infrastructure
elements extend the link to support communications between Clients
as single-hop neighbors.
OMNI interface
a node's attachment to an OMNI link, and configured over one or
more underlay interfaces. If there are multiple OMNI links in an
OMNI domain, a separate OMNI interface is configured for each
link. The OMNI interface configures a Maximum Transmission Unit
(MTU) and a Maximum Reassembly Unit (MRU) the same as any
interface.
OMNI Adaptation Layer (OAL)
an OMNI interface sublayer service that encapsulates original IP
packets admitted into the interface in an IPv6 header and/or
subjects them to fragmentation and reassembly. The OAL is also
responsible for generating MTU-related control messages as
necessary, and for providing addressing context for OMNI link SRT
traversal. The OAL presents a new layer in the Internet
architecture known simply as the "adaptation layer".
Host
an end user device that extends the OMNI link over an ENET
interface serviced by a Client. (As an implementation matter, the
Host either assigns the same IP address from the ENET (underlay)
interface to an (overlay) OMNI interface, or configures an OMNI-
like function as a virtual sublayer of the ENET interface itself.)
The IP addresses assigned to each Host ENET interface remain
stable even if the Client's upstream *NET interface connections
change.
Client
a network platform/device mobile router that configures one or
more OMNI interfaces over distinct sets of underlay interfaces
grouped as logical OMNI link units. The Client coordinates with
the Mobility Service via upstream networks over *NET interfaces,
and provides Proxy/Server services for Hosts and other Clients on
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ENET interface downstream networks. The Client's *NET interface
addresses and performance characteristics may change over time
(e.g., due to node mobility, link quality, etc.) while downstream-
attached Hosts and other Clients see the ENET as a stable ANET.
Proxy/Server
a segment routing topology edge node that configures an OMNI
interface and connects Clients to the Mobility Service. As a
server, the Proxy/Server responds directly to some Client IPv6 ND
messages. As a proxy, the Proxy/Server forwards other Client IPv6
ND messages to other Proxy/Servers and Clients. As a router, the
Proxy/Server provides a forwarding service for ordinary data
packets that may be essential in some environments and a last
resort in others. Proxy/Servers at ANET boundaries configure both
an ANET downstream interface and *NET upstream interface, while
INET-based Proxy/Servers configure only an INET interface.
First-Hop Segment (FHS) Proxy/Server
a Proxy/Server connected to the source Client's *NET that forwards
packets sent by the source into the segment routing topology. FHS
Proxy/Servers also act as intermediate forwarding nodes to
facilitate RS/RA exchanges between Clients and Hub Proxy/Servers.
Last-Hop Segment (LHS) Proxy/Server
a Proxy/Server connected to the target Client's *NET that forwards
packets received from the segment routing topology to the target.
Hub Proxy/Server
a single Proxy/Server selected by the Client that provides a
designated router service for all of the Client's*NET underlay
networks. Since all Proxy/Servers provide equivalent services,
Clients normally select the first FHS Proxy/Server they coordinate
with to serve as the Hub. However, the Hub can also be any
available Proxy/Server for the OMNI link, i.e., and not
necessarily one of the Client's FHS Proxy/Servers.
Segment Routing Topology (SRT)
a multinet forwarding region configured over one or more INETs
between the FHS Proxy/Server and LHS Proxy/Server. The SRT spans
the OMNI link on behalf of source/target Client pairs using
segment routing in a manner outside the scope of this document
(see: [I-D.templin-6man-aero]).
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Mobility Service (MS)
a mobile routing service that tracks Client movements and ensures
that Clients remain continuously reachable even across mobility
events. The MS consists of the set of all Proxy/Servers and any
other OMNI link supporting infrastructure nodes. Specific MS
details are out of scope for this document, with an example found
in [I-D.templin-6man-aero].
Mobility Service Prefix (MSP)
an aggregated IP Global Unicast Address (GUA) prefix (e.g.,
2001:db8::/32, 192.0.2.0/24, etc.) assigned to the OMNI link and
from which more-specific Mobile Network Prefixes (MNPs) are
delegated. OMNI link administrators typically obtain MSPs from an
Internet address registry, however private-use prefixes can also
be used subject to certain limitations (see: Section 10). OMNI
links that connect to the global Internet advertise their MSPs to
their interdomain routing peers.
Mobile Network Prefix (MNP)
a longer IP prefix delegated from an MSP (e.g.,
2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a
Client. Clients receive MNPs from Proxy/Servers and sub-delegate
them to routers, Hosts and other Clients located in ENETs.
original IP packet
a whole IP packet or fragment admitted into the OMNI interface by
the network layer prior to OAL encapsulation and fragmentation, or
an IP packet delivered to the network layer by the OMNI interface
following OAL decapsulation and reassembly.
OAL packet
an original IP packet encapsulated in an IPv6 header (i.e., the
OAL header) then submitted for OAL fragmentation and reassembly.
OAL fragment
a portion of an OAL packet following fragmentation but prior to
encapsulation, or following encapsulation but prior to OAL
reassembly.
(OAL) atomic fragment
an OAL packet that does not require fragmentation is always
encapsulated as an "atomic fragment" with a Fragment Header with
Fragment Offset and More Fragments both set to 0, but with a valid
Identification value.
(OAL) carrier packet
an encapsulated OAL fragment following L2 encapsulation or prior
to L2 decapsulation. OAL sources and destinations exchange
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carrier packets over underlay interfaces, and may be separated by
one or more OAL intermediate nodes. OAL intermediate nodes may
perform re-encapsulation on carrier packets by removing the L2
headers of the first hop network and replacing them with new L2
headers for the next hop network. (The term "carrier" honors
agents of the service postulated by [RFC1149] and [RFC6214].)
OAL source
an OMNI interface acts as an OAL source when it encapsulates
original IP packets to form OAL packets, then performs OAL
fragmentation and encapsulation to create carrier packets.
OAL destination
an OMNI interface acts as an OAL destination when it decapsulates
carrier packets, then performs OAL reassembly and decapsulation to
derive the original IP packet.
OAL intermediate node
an OMNI interface acts as an OAL intermediate node when it removes
the L2 encapsulation headers of carrier packets received on a
first segment, then re-encapsulates the carrier packets in new L2
encapsulation headers and forwards them into the next segment.
OMNI Option
an IPv6 Neighbor Discovery option providing multilink parameters
for the OMNI interface as specified in Section 12.
Mobile Network Prefix Link Local Address (MNP-LLA)
an IPv6 Link Local Address that embeds the most significant 64
bits of an MNP in the lower 64 bits of fe80::/64, as specified in
Section 8.
Mobile Network Prefix Unique Local Address (MNP-ULA)
an IPv6 Unique-Local Address derived from an MNP-LLA as discussed
in Section 9.
Mobile Network Prefix eXtended Local Address (MNP-XLA)
an IPv6 Unique-Local Address that embeds the most significant 64
bits of an MNP in the lower 64 bits of fd00::/64, as specified in
Section 9. (Note that MNP-XLAs can be formed from MNP-LLAs simply
by inverting bits 7 and 8 of 'fe80' to form 'fd00'.)
Administrative Link Local Address (ADM-LLA)
an IPv6 Link Local Address that embeds a 56-bit randomly-
initialized identification value in the lower 56 bits of
fe80::/80, as specified in Section 8.
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Administrative Unique Local Address (ADM-ULA)
an IPv6 Unique-Local Address derived from an ADM-LLA as discussed
in Section 9.
Temporary Unique Local Address (TMP-ULA)
an IPv6 Unique-Local Address configured by a Client that embeds a
112-bit randomly-initialized identification value in the lower 112
bits of fd00:/16, as specified in Section 9. Clients use TMP-ULAs
(and/or MNP-XLAs) to bootstrap autoconfiguration in the presence
of OMNI link infrastructure, while continued use of TMP-ULAs may
be necessary in the absence of infrastructure. (Note that in some
environments Clients can instead use a (Hierarchical) Host
Identity Tag ((H)HIT) instead of a TMP-ULA - see: Section 22.)
Multilink
a Client OMNI interface's manner of managing multiple diverse *NET
underlay interfaces as a single logical unit. The OMNI interface
provides a single unified interface to upper layers, while
underlay interface selections are performed on a per-packet basis
considering traffic selectors such as DSCP, flow label,
application policy, signal quality, cost, etc. Multilink
selections are coordinated in both the outbound and inbound
directions based on source/target underlay interface pairs.
Multinet
an intermediate node's manner of spanning multiple diverse IP
Internetwork and/or private enterprise network "segments" at the
OAL layer below IP. Through intermediate node concatenation of
SRT network segments, multiple diverse Internetworks (such as the
global public IPv4 and IPv6 Internets) can serve as transit
segments in an end-to-end L2 forwarding path. This OAL
concatenation capability provides benefits such as supporting
IPv4/IPv6 transition and coexistence, joining multiple diverse
operator networks into a cooperative single service network, etc.
See: [I-D.templin-6man-aero] for further information.
Multihop
an iterative relaying of IP packets between Client's over an OMNI
underlay interface technology (such as omnidirectional wireless)
without support of fixed infrastructure. Multihop services entail
Client-to-Client relaying within a Mobile/Vehicular Ad-hoc Network
(MANET/VANET) for Vehicle-to-Vehicle (V2V) communications and/or
for Vehicle-to-Infrastructure (V2I) "range extension" where
Clients within range of communications infrastructure elements
provide forwarding services for other Clients.
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Mobility
any action that results in a change to a Client underlay interface
address. The change could be due to, e.g., a handover to a new
wireless base station, loss of link due to signal fading, an
actual physical node movement, etc.
Safety-Based Multilink (SBM)
A means for ensuring fault tolerance through redundancy by
connecting multiple OMNI interfaces within the same domain to
independent routing topologies (i.e., multiple independent OMNI
links).
Performance Based Multilink (PBM)
A means for selecting one or more underlay interface(s) for packet
transmission and reception within a single OMNI interface.
OMNI Domain
The set of all SBM/PBM OMNI links that collectively provides
services for a common set of MSPs. All OMNI links within the same
domain configure, advertise and respond to the same OMNI IPv6
Anycast address(es).
Multilink Forwarding Information Base (MFIB)
A forwarding table on each OMNI source, destination and
intermediate node that includes Multilink Forwarding Vectors (MFV)
with both next hop forwarding instructions and context for
reconstructing compressed headers for specific underlay interface
pairs used to communicate with peers. See:
[I-D.templin-6man-aero] for further discussion.
Multilink Forwarding Vector (MFV)
An MFIB entry that includes soft state for each underlay interface
pairwise communication session between peers. MFVs are identified
by both a next-hop and previous-hop MFV Index (MFVI), with the
next-hop established based on an IPv6 ND solicitation and the
previous hop established based on the solicited IPv6 ND
advertisement response. See: [I-D.templin-6man-aero] for further
discussion.
Multilink Forwarding Vector Index (MVFI)
A 4 octet value selected by an OMNI node when it creates an MFV,
then advertised to either a next-hop or previous-hop. OMNI
intermediate nodes assign two distinct MFVIs for each MFV and
advertise one to the next-hop and the other to the previous-hop.
OMNI end systems assign and advertise a single MFVI. See:
[I-D.templin-6man-aero] for further discussion.
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IP Jumbogram
an IPv4 or IPv6 packet with a Jumbo Payload option that includes a
32-bit length field to be used instead of the 16-bit {Total,
Payload} Length field (see: Section 5.1). For IPv4, the Total
Length field must be set to the length of the IPv4 header only.
For IPv6, the Payload Length must be set to 0.
IP Parcel
a special form of an IP Jumbogram with a segment length value
included in the {Total, Payload} Length field and also with a
Jumbo Payload option (see: Section 5.2).
INADDR
the IP address (and also the UDP port number when UDP is used)
that appears in (L2) encapsulation headers in the data plane and
in IPv6 ND OMNI option sub-options in the control plane.
3. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
An implementation is not required to internally use the architectural
constructs described here so long as its external behavior is
consistent with that described in this document.
4. Overlay Multilink Network (OMNI) Interface Model
An OMNI interface is a virtual interface configured over one or more
underlay interfaces, which may be physical (e.g., an aeronautical
radio link, etc.) or virtual (e.g., an Internet or higher-layer
"tunnel"). The OMNI interface architectural layering model is the
same as in [RFC5558][RFC7847], and augmented as shown in Figure 1.
The IP layer therefore sees the OMNI interface as a single L3
interface nexus for multiple underlay interfaces that appear as L2
communication channels in the architecture.
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+----------------------------+
| Upper Layer Protocol |
Session-to-IP +---->| |
Address Binding | +----------------------------+
+---->| IP (L3) |
IP Address +---->| |
Binding | +----------------------------+
+---->| OMNI Interface |
Logical-to- +---->| (OMNI Adaptation Layer) |
Physical | +----------------------------+
Interface +---->| L2 | L2 | | L2 |
Binding |(IF#1)|(IF#2)| ..... |(IF#n)|
+------+------+ +------+
| L1 | L1 | | L1 |
| | | | |
+------+------+ +------+
Figure 1: OMNI Interface Architectural Layering Model
Each underlay interface provides an L2/L1 abstraction according to
one of the following models:
* ANET interfaces connect to a protected and secured ANET that is
separated from the open INET by Proxy/Servers. The ANET interface
may be either on the same L2 link segment as a Proxy/Server, or
separated from a Proxy/Server by multiple IP hops. (Note that
NATs may appear internally within an ANET or on the Proxy/Server
itself and may require NAT traversal the same as for the INET
case.)
* INET interfaces connect to an INET either natively or through one
or several IPv4 Network Address Translators (NATs). Native INET
interfaces have global IP addresses that are reachable from any
INET correspondent. NATed INET interfaces typically configure
private IP addresses and connect to a private network behind one
or more NATs with the outermost NAT providing INET access.
* ENET interfaces connect a Client's downstream-attached networks,
where the Client provides forwarding services for ENET Host and
Client communications to remote peers. An ENET may be as simple
as a small stub network that travels with a mobile Client (e.g.,
an Internet-of-Things) to as complex as a large private enterprise
network that the Client connects to a larger ANET or INET.
Downstream-attached Hosts and Clients see the ENET as an ANET and
see the (upstream) Client as a Proxy/Server.
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* VPNed interfaces use security encapsulation over an underlay
network to a Client or Proxy/Server acting as a Virtual Private
Network (VPN) gateway. Other than the link-layer encapsulation
format, VPNed interfaces behave the same as for Direct interfaces.
* Direct (aka "point-to-point") interfaces connect directly to a
Client or Proxy/Server without crossing any networked paths. An
example is a line-of-sight link between a remote pilot and an
unmanned aircraft.
The OMNI interface forwards original IP packets from the network
layer (L3) using the OMNI Adaptation Layer (OAL) (see: Section 5) as
an encapsulation and fragmentation sublayer service. This "OAL
source" then further encapsulates the resulting OAL packets/fragments
in underlay network headers (e.g., UDP/IP, IP-only, Ethernet-only,
etc.) to create L2-encapsulated "carrier packets" for transmission
over underlay interfaces. The target OMNI interface receives the
carrier packets from underlay interfaces and discards the L2
encapsulation headers. If the resulting OAL packets/fragments are
addressed to itself, the OMNI interface acts as an "OAL destination"
and performs reassembly if necessary, discards the OAL encapsulation,
and delivers the original IP packet to the network layer. If the OAL
fragments are addressed to another node, the OMNI interface instead
acts as an "OAL intermediate node" by re-encapsulating the carrier
packets in new underlay network L2 headers and forwarding them over
an underlay interface without reassembling or discarding the OAL
encapsulation. The OAL source and OAL destination are seen as
"neighbors" on the OMNI link, while OAL intermediate nodes provide a
virtual bridging service that joins the segments of a (multinet)
Segment Routing Topology (SRT).
The OMNI interface can forward original IP packets over underlay
interfaces while including/omitting various lower layer
encapsulations including OAL, UDP, IP and Ethernet (ETH) or other
link-layer header. The network layer can also access the underlay
interfaces directly while bypassing the OMNI interface entirely when
necessary. This architectural flexibility may be beneficial for
underlay interfaces (e.g., some aviation data links) for which
encapsulation overhead may be a primary consideration. OMNI
interfaces that send original IP packets directly over underlay
interfaces without invoking the OAL can only reach peers located on
the same OMNI link segment. Source Clients can instead use the OAL
to coordinate with target Clients in the same or different OMNI link
segments by sending initial carrier packets to a First-Hop Segment
(FHS) Proxy/Server. The FHS Proxy/Sever then forwards the packets
into the SRT spanning tree, which transports them to a Last-Hop
Segment (LHS) Proxy/Server for the target Client.
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Original IP packets sent directly over underlay interfaces are
subject to the same path MTU related issues as for any
Internetworking path, and do not include per-packet identifications
that can be used for data origin verification and/or link-layer
retransmissions. Original IP packets presented directly to an
underlay interface that exceed the underlay network path MTU are
dropped with an ordinary ICMPv6 Packet Too Big (PTB) message
returned. These PTB messages are subject to loss [RFC2923] the same
as for any non-OMNI IP interface.
The OMNI interface encapsulation/decapsulation layering possibilities
are shown in Figure 2 below. Imaginary vertical lines drawn between
the Network Layer and Underlay interfaces in the figure denote the
encapsulation/decapsulation layering combinations possible. Common
combinations include IP-only (i.e., direct access to underlay
interfaces with or without using the OMNI interface), IP/IP, IP/UDP/
IP, IP/UDP/IP/ETH(ERNET), IP/OAL/UDP/IP, IP/OAL/UDP/ETH, etc.
+------------------------------------------------------------+ ^
| Network Layer (Original IP packets) | |
+--+---------------------------------------------------------+ L3
| OMNI Interface (virtual sublayer nexus) | |
+--------------------------+------------------------------+ -
| OAL Encaps/Decaps | |
+------------------------------+ OAL
| OAL Frag/Reass | |
+------------+---------------+--------------+ -
| UDP Encaps/Decaps/Compress | |
+----+---+------------+--------+--+ +--------+ |
| IP E/D | | IP E/D | | IP E/D | L2
+----+-----+--+----+ +--+----+---+ +---+----+--+ |
|ETH E/D| |ETH E/D| |ETH E/D| |ETH E/D| |
+------+-------+--+-------+----+-------+-------------+-------+ v
| Underlay Interfaces |
+------------------------------------------------------------+
Figure 2: OMNI Interface Layering
The OMNI/OAL model gives rise to a number of opportunities:
* Clients receive MNPs from the MS, and coordinate with the MS
through IPv6 ND message exchanges with Proxy/Servers. Clients use
the MNP to construct a unique Link-Local Address (MNP-LLA) through
the algorithmic derivation specified in Section 8 and assign the
LLA to the OMNI interface. Since MNP-LLAs are uniquely derived
from an MNP, no Duplicate Address Detection (DAD) or Multicast
Listener Discovery (MLD) messaging is necessary.
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* since Temporary ULAs (TMP-ULAs) are statistically unique, they can
be used without DAD until an MNP is obtained.
* underlay interfaces on the same L2 link segment as a Proxy/Server
do not require any L3 addresses (i.e., not even link-local) in
environments where communications are coordinated entirely over
the OMNI interface.
* as underlay interface properties change (e.g., link quality, cost,
availability, etc.), any active interface can be used to update
the profiles of multiple additional interfaces in a single
message. This allows for timely adaptation and service continuity
under dynamically changing conditions.
* coordinating underlay interfaces in this way allows them to be
represented in a unified MS profile with provisions for mobility
and multilink operations.
* exposing a single virtual interface abstraction to the IPv6 layer
allows for multilink operation (including QoS based link
selection, packet replication, load balancing, etc.) at L2 while
still permitting L3 traffic shaping based on, e.g., DSCP, flow
label, etc.
* the OMNI interface allows multinet traversal over the SRT when
communications across different administrative domain network
segments are necessary. This mode of operation would not be
possible via direct communications over the underlay interfaces
themselves.
* the OAL supports lossless and adaptive path MTU mitigations not
available for communications directly over the underlay interfaces
themselves. The OAL supports "packing" of multiple IP payload
packets within a single OAL "super-packet" and also supports
transmission of IP packets and parcels of all sizes up to and
including Jumbograms.
* the OAL applies per-packet identification values that allow for
link-layer reliability and data origin authentication.
* L3 sees the OMNI interface as a point of connection to the OMNI
link; if there are multiple OMNI links, L3 will see multiple OMNI
interfaces.
* Multiple independent OMNI interfaces can be used for increased
fault tolerance through Safety-Based Multilink (SBM), with
Performance-Based Multilink (PBM) applied within each interface.
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* Multiple independent OMNI links can be joined together into a
single link without requiring renumbering of infrastructure
elements, since the ADM-ULAs assigned to the different links will
be mutually exclusive.
* the OMNI/OAL model supports transmission of a new form of IP
packets known as "IP Parcels" that improve performance and
efficiency for both upper layer protocols and networked paths.
Note that even when the OMNI virtual interface is present,
applications can still access underlay interfaces either through the
network protocol stack using an Internet socket or directly using a
raw socket. This allows for intra-network (or point-to-point)
communications without invoking the OMNI interface and/or OAL. For
example, when an OMNI interface is configured over an underlay IP
interface, applications can still invoke intra-network IP
communications directly over the underlay interface as long as the
communicating endpoints are not subject to mobility dynamics.
Figure 3 depicts the architectural model for a source Client with an
attached ENET connecting to the OMNI link via multiple independent
ANETs/INETs (i.e., *NETs). The Client's OMNI interface sends IPv6 ND
solicitation messages over available *NET underlay interfaces using
any necessary L2 encapsulations. The IPv6 ND messages traverse the
*NETs until they reach an FHS Proxy/Server (FHS#1, FHS#2, ...,
FHS#n), which returns an IPv6 ND advertisement message and/or
forwards a proxyed version of the message over the SRT to an LHS
Proxy/Server near the target Client (LHS#1, LHS#2, ..., LHS#m). The
Hop Limit in IPv6 ND messages is not decremented due to
encapsulation; hence, the source and target Client OMNI interfaces
appear to be attached to a common link.
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+--------------+
|Source Client |
+--------------+ (:::)-.
|OMNI interface|<-->.-(::ENET::)
+----+----+----+ `-(::::)-'
+--------|IF#1|IF#2|IF#n|------ +
/ +----+----+----+ \
/ | \
/ | \
v v v
(:::)-. (:::)-. (:::)-.
.-(::*NET:::) .-(::*NET:::) .-(::*NET:::)
`-(::::)-' `-(::::)-' `-(::::)-'
+-----+ +-----+ +-----+
... |FHS#1| ......... |FHS#2| ......... |FHS#n| ...
. +--|--+ +--|--+ +--|--+ .
. | | |
. \ v / .
. \ / .
. v (:::)-. v .
. .-(::::::::) .
. .-(::: Segment :::)-. .
. (::::: Routing ::::) .
. `-(:: Topology ::)-' .
. `-(:::::::-' .
. / | \ .
. / | \ .
. v v v
. +-----+ +-----+ +-----+ .
... |LHS#1| ......... |LHS#2| ......... |LHS#m| ...
+--|--+ +--|--+ +--|--+
\ | /
v v v
<-- Target Clients -->
Figure 3: Source/Target Client Coordination over the OMNI Link
After the initial IPv6 ND message exchange, the source Client (as
well as any nodes on its attached ENETs) can send packets to the
target Client over the OMNI interface. OMNI interface multilink
services will forward the packets via FHS Proxy/Servers for the
correct underlay *NETs. The FHS Proxy/Server then forwards the
packets over the SRT which delivers them to an LHS Proxy/Server, and
the LHS Proxy/Server in turn forwards them to the target Client.
(Note that when the source and target Client are on the same SRT
segment, the FHS and LHS Proxy/Servers may be one and the same.)
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Clients select a Hub Proxy/Server (not shown in the figure), which
will often be one of their FHS Proxy/Servers but could also be any
Proxy/Server on the OMNI link. Clients then register all of their
*NET underlay interfaces with the Hub Proxy/Server via the FHS Proxy/
Server in a pure proxy role. The Hub Proxy/Server then provides a
designated router service for the Client, and the Client can quickly
migrate to a new Hub Proxy/Server if the first becomes unresponsive.
Clients therefore use Proxy/Servers as gateways into the SRT to reach
OMNI link correspondents via a spanning tree established in a manner
outside the scope of this document. Proxy/Servers forward critical
MS control messages via the secured spanning tree and forward other
messages via the unsecured spanning tree (see Security
Considerations). When route optimization is applied as discussed in
[I-D.templin-6man-aero], Clients can instead forward directly to SRT
intermediate nodes (or directly to correspondents in the same SRT
segment) to reduce Proxy/Server load.
Note: while not shown in the figure, a Client's ENET may connect many
additional Hosts and even other Clients in a recursive extension of
the OMNI link. This OMNI virtual link extension will be discussed
more fully throughout the document.
5. OMNI Interface Maximum Transmission Unit (MTU)
The OMNI interface observes the link nature of tunnels, including the
Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and
the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels].
The OMNI interface is configured over one or more underlay interfaces
as discussed in Section 4, where the interfaces (and their associated
underlay network paths) may have diverse MTUs. OMNI interface
considerations for accommodating original IP packets of various sizes
are discussed in the following sections.
IPv6 underlay interfaces are REQUIRED to configure a minimum MTU of
1280 octets and a minimum MRU of 1500 octets [RFC8200]. Therefore,
the minimum IPv6 path MTU is 1280 octets since routers on the path
are not permitted to perform network fragmentation even though the
destination is required to reassemble more. The network therefore
MUST forward original IP packets of at least 1280 octets without
generating an IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB)
message [RFC8201]. (While the source can apply "source
fragmentation" for locally-generated IPv6 packets up to 1500 octets
and larger still if it knows the destination configures a larger MRU,
this does not affect the minimum IPv6 path MTU.)
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IPv4 underlay interfaces are REQUIRED to configure a minimum MTU of
68 octets [RFC0791] and a minimum MRU of 576 octets
[RFC0791][RFC1122]. Therefore, when the Don't Fragment (DF) bit in
the IPv4 header is set to 0 the minimum IPv4 path MTU is 576 octets
since routers on the path support network fragmentation and the
destination is required to reassemble at least that much. The OMNI
interface therefore MUST set DF to 0 in the IPv4 encapsulation
headers of carrier packets that are no larger than 576 octets, and
SHOULD set DF to 1 in larger carrier packets unless it has a way to
determine the encapsulation destination MRU and has carefully
considered the issues discussed in Section 6.12.
When the network layer admits an original IP packet into the OMNI
interface the OAL prepends an IPv6 encapsulation header (see:
Section 6) where the 16-bit Payload Length field limits the maximum-
sized original IP packet to (2**16 -1) = 65535 octets; this is also
the maximum size that the OAL can accommodate with IPv6
fragmentation. The OMNI interface therefore sets an MTU and MRU of
65535 octets to support assured delivery of original packets no
larger than this size even if IPv6 fragmentation is required. (The
OMNI interface MAY set a larger MTU to support best-effort delivery
for larger packets; see below.) The OMNI interface then employs the
OAL as an encapsulation sublayer service to transform original IP
packets into OAL packets/fragments, and the OAL in turn uses underlay
network encapsulation to forward carrier packets over underlay
interfaces (see: Section 6).
5.1. Jumbograms
While the maximum-sized original IP packet that the OAL can
accommodate using IPv6 fragmentation is 65535 octets, OMNI interfaces
can forward still larger IPv6 packets as OAL "atomic fragments"
through the application of IPv6 Jumbograms [RFC2675]. For such
larger packets, the OMNI interface performs OAL encapsulation by
appending an IPv6 header followed by an 8-octet Hop-By-Hop header
with Jumbo Payload option followed by a Routing Header of no more
than 40-octets (if necessary) and finally followed by an 8-octet
Fragment Header.
Since the Jumbo Payload option includes a 32-bit length field, OMNI
interfaces can therefore configure a larger IP MTU up to a maximum of
((2**32 - 1) - 8 - 40 - 8) = 4294967239 octets. In that case, the
OAL will still provide original IP packets no larger than 65535 with
an IPv6 fragmentation-based assured delivery service while larger IP
packets will receive a best-effort delivery service as atomic
fragments (note that the OAL destination is permitted to accept
atomic fragments that exceed the OMNI interface MRU).
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The OAL source forwards jumbo atomic fragments under the assumption
that upper and lower layers will employ sufficient integrity
assurance, noting that commonly-used 32-bit CRCs may be inadequate
for these larger sizes [CRC]. If the packet is dropped along the
path to the OAL destination, the OAL source must arrange to return a
PTB "hard error" to the original source Section 6.8.
This document notes that a Jumbogram service for IPv4 is also
specified in [I-D.templin-intarea-parcels], where all OMNI link
aspects of the service are conducted in a similar fashion as for IPv6
above.
5.2. IPv6 Parcels
As specified in [I-D.templin-intarea-parcels], an IP Parcel is a
variation of the IP Jumbogram construction beginning with an IP
header with the length of the first upper layer protocol segment in
the {Total, Payload} Length field, but with a Jumbo Payload option
with a length that may be the same as or larger than the length in
the IP header. The differences in these lengths determines the size
and number of upper layer protocol segments within the parcel.
The IP Parcel format and transmission/reception procedures for OMNI
interfaces are specified in Section 6.14. End systems that implement
either the full OMNI interface (i.e., Clients) or enough of the OAL
to process parcels (i.e., Hosts) are permitted to exchange parcels
with consenting peers.
6. The OMNI Adaptation Layer (OAL)
When an OMNI interface forwards an original IP packet from the
network layer for transmission over one or more underlay interfaces,
the OMNI Adaptation Layer (OAL) acting as the OAL source applies
encapsulation to form OAL packets subject to fragmentation producing
OAL fragments suitable for L2 encapsulation and transmission as
carrier packets over underlay interfaces as described in Section 6.1.
These carrier packets travel over one or more underlay networks
spanned by OAL intermediate nodes in the SRT, which re-encapsulate by
removing the L2 headers of the first underlay network and appending
L2 headers appropriate for the next underlay network in succession.
(This process supports the multinet concatenation capability needed
for joining multiple diverse networks.) After re-encapsulation by
zero or more OAL intermediate nodes, the carrier packets arrive at
the OAL destination.
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When the OAL destination receives the carrier packets, it discards
the L2 headers and reassembles the resulting OAL fragments (if
necessary) into an OAL packet as described in Section 6.3. The OAL
destination next decapsulates the OAL packet to obtain the original
IP packet then delivers the original IP packet to the network layer.
The OAL source may be either the source Client or its FHS Proxy/
Server, while the OAL destination may be either the LHS Proxy/Server
or the target Client. Proxy/Servers (and SRT Gateways as discussed
in [I-D.templin-6man-aero]) may also serve as OAL intermediate nodes.
The OAL presents an OMNI sublayer abstraction similar to ATM
Adaptation Layer 5 (AAL5). Unlike AAL5 which performs segmentation
and reassembly with fixed-length 53 octet cells over ATM networks,
however, the OAL uses IPv6 encapsulation, fragmentation and
reassembly with larger variable-length cells over heterogeneous
underlay networks. Detailed operations of the OAL are specified in
the following sections.
6.1. OAL Source Encapsulation and Fragmentation
When the network layer forwards an original IP packet into the OMNI
interface, the OAL source creates an "OAL packet" by prepending an
IPv6 OAL encapsulation header per [RFC2473] but does not decrement
the Hop Limit/TTL of the original IP packet since encapsulation
occurs at a layer below IP forwarding. The OAL source copies the
"Type of Service/Traffic Class" [RFC2983] and "Explicit Congestion
Notification (ECN)" [RFC3168] values in the original packet's IP
header into the corresponding fields in the OAL header, then sets the
OAL header "Flow Label" as specified in [RFC6438]. The OAL source
finally sets the OAL header IPv6 Payload Length to the length of the
original IP packet and sets Hop Limit to a value that MUST NOT be
larger than 63 yet is still sufficiently large to enable loop-free
forwarding over multiple concatenated OMNI link intermediate hops.
The OAL next selects OAL packet source and destination addresses.
Client OMNI interfaces set the OAL source address to a Unique Local
Address (ULA) based on the Mobile Network Prefix (MNP-ULA), while
Proxy/Server OMNI interfaces set the source address to an
Administrative ULA (ADM-ULA) (see: Section 9). When a Client OMNI
interface does not (yet) have an MNP, it can use a Temporary ULA
(TMP-ULA) (see: Section 22) and/or (Hierarchical) Host Identity Tag
((H)HIT) instead (see: Section 22) as OAL addresses. (In addition to
ADM-ULAs, Proxy/Servers also process packets with anycast and/or
multicast OAL addresses.)
The OAL source next selects a 32-bit OAL packet Identification value
as specified in Section 6.6. The OAL then calculates a 2-octet OAL
checksum using the algorithm specified in Appendix A. The OAL source
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calculates the checksum over the OAL packet beginning with a pseudo-
header of the OAL header similar to that found in Section 8.1 of
[RFC8200], then extending over the entire length of the original IP
packet. The OAL pseudo-header is formed as shown in Figure 4:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ OAL Source Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ OAL Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL Payload Length | zero | Next Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: OAL Pseudo-Header
After calculating the checksum, the OAL source next fragments the OAL
packet if necessary while assuming the IPv4 minimum path MTU (i.e.,
576 octets) as the worst case for OAL fragmentation regardless of the
underlay interface IP protocol version since IPv6/IPv4 protocol
translation and/or IPv6-in-IPv4 encapsulation may occur in any
underlay network path. By initially assuming the IPv4 minimum even
for IPv6 underlay interfaces, the OAL source may produce smaller
fragments with additional encapsulation overhead but avoids loss due
to presenting an underlay interface with a carrier packet that
exceeds its MRU. Additionally, the OAL path could traverse multiple
SRT segments with intermediate OAL forwarding nodes performing re-
encapsulation where the L2 encapsulation of the previous segment is
replaced by the L2 encapsulation of the next segment which may be
based on a different IP protocol version and/or encapsulation sizes.
The OAL source therefore assumes a default minimum path MTU of 576
octets at each SRT segment for the purpose of generating OAL
fragments for L2 encapsulation and transmission as carrier packets.
Each successive SRT intermediate node may include either a 20 octet
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IPv4 or 40 octet IPv6 header, an 8 octet UDP header and in some cases
an IP security encapsulation (40 octets maximum assumed) during re-
encapsulation. Intermediate nodes at any SRT segment may also insert
or modify the Routing Header (40 octets maximum) following the 40
octet OAL IPv6 header and preceding the 8 octet Fragment Header.
Therefore, assuming a worst case of (40 + 40 + 8) = 88 octets for L2
encapsulations plus (40 + 40 + 8) = 88 octets for OAL encapsulation
leaves no less than (576 - 88 - 88) = 400 octets remaining to
accommodate a portion of the original IP packet/fragment. The OAL
source therefore sets a minimum Maximum Payload Size (MPS) of 400
octets as the basis for the minimum-sized OAL fragment that can be
assured of traversing all SRT segments without loss due to an MTU/MRU
restriction. The Maximum Fragment Size (MFS) for OAL fragmentation
is therefore determined by the MPS plus the size of the OAL
encapsulation headers.
The OAL source SHOULD maintain "path MPS" values for individual OAL
destinations initialized to the minimum MPS and increased to larger
values if better information is known or discovered. For example,
when peers share a common underlay network link or a fixed path with
a known larger MTU, the OAL source can set path MPS to a larger size
(i.e., greater than 400 octets) as long as the peer reassembles
before re-encapsulating and forwarding (while re-fragmenting if
necessary). Also, if the OAL source has a way of knowing the maximum
L2 encapsulation size for all SRT segments along the path it may be
able to increase path MPS to reserve additional room for payload
data. Even when OAL header compression is used, the OAL source must
include the uncompressed OAL header size in its path MPS calculation
since it may need to include a full header at any time.
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The OAL source can also optimistically set a larger path MPS and/or
actively probe individual OAL destinations to discover larger sizes
using packetization layer probes in a similar fashion as
[RFC4821][RFC8899], but care must be taken to avoid setting static
values for dynamically changing paths leading to black holes. The
probe involves sending an OAL packet larger than the current path MPS
and receiving a small acknowledgement response (with the possible
receipt of link-layer error message when a probe is lost). For this
purpose, the OAL source can send an NS message with one or more OMNI
options with large PadN sub-options (see: Section 12) and/or with a
trailing large NULL packet in a super-packet (see: Section 6.9) in
order to receive a small NA response from the OAL destination. While
observing the minimum MPS will always result in robust and secure
behavior, the OAL source should optimize path MPS values when more
efficient utilization may result in better performance (e.g. for
wireless aviation data links). The OAL source should maintain
separate path MPS values for each (source, target) underlay interface
pair for the same OAL destination, since different underlay interface
pairs may support differing path MPS values.
When the OAL source performs fragmentation, it SHOULD produce the
minimum number of non-overlapping fragments under current MPS
constraints, where each non-final fragment MUST be at least as large
as the minimum MPS, while the final fragment MAY be smaller. The OAL
source also converts all original IP packets no larger than the
current MPS (or larger than 65535 octets) into atomic fragments by
including a Fragment Header with Fragment Offset and More Fragments
both set to 0. The OAL source then inserts a Routing Header (if
necessary) following the IPv6 encapsulation header and before the
Fragment Header. If the original IP packet is larger than 65535, the
OAL source also inserts a Hop-By-Hop header with Jumbo Payload option
immediately following the IPv6 encapsulation header and before the
Routing Header (if necessary), then includes an (atomic) Fragment
Header. The header extension order for each fragment therefore
appears as the OAL IPv6 header followed by Hop-By-Hop header followed
by Routing Header followed by Fragment Header.
The OAL source next appends the OAL checksum as the final two octets
of the final fragment while increasing its (Jumbo) Payload Length by
2. If appending the checksum would cause the final fragment to
exceed the current MPS, the OAL source instead reduces this "former"
final fragment's Payload Length (PL) by (N*8 + (PL mod 8)) octets,
where N is an integer that would result in a non-zero reduction but
without causing the former final fragment to become smaller than the
minimum MPS. The OAL source then creates a "new" final fragment by
copying the OAL IPv6 header and extension headers from the former
final fragment, then copying the (N*8 + (PL mod 8)) octets from the
end of the former final fragment immediately following the new final
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fragment extension headers. The OAL source then sets the former
final fragment's More Fragments flag to 1, increments the new final
fragment's fragment offset by the former final fragment's new (PL /
8) and finally appends the checksum the same as discussed above.
Next, the OAL source replaces the IPv6 Fragment Header 1-octet
"Reserved" field (and for first fragments also the 2-bit "Reserved
Flags" field) with OMNI-specific encodings as shown in:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Parcel ID |A| Fragment Offset |P|S|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
a) First fragment
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Ordinal |A| Fragment Offset |Res|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
a) Non-first fragment
Figure 5: IPv6 Fragment Header Reserved Fields Redefined
For the first fragment, the OAL source sets the "(A)RQ" flag then
sets "Parcel ID", "(P)arcel" and "(S)ub-Parcels" as specified in
Section 6.14. For each non-first fragment, the OAL source instead
sets the "(A)RQ" flag and writes a monotonically-increasing "Ordinal"
value between 1 and 127. Specifically, the OAL source writes the
ordinal number '1' for the first non-first fragment, '2' for the
second, '3' for the third, etc. up to the final fragment or the
ordinal value '127', whichever comes first. (For any additional non-
first fragments beyond ordinal '127', the OAL source instead writes
the value '0' in the Ordinal field and clears the "(A)RQ" flag. The
first fragment is implicitly always considered ordinal number '0'
even though the header does not include an explicit Ordinal field.)
The OAL source finally encapsulates the fragments in L2 headers to
form carrier packets and forwards them over an underlay interface,
while retaining the fragments and their ordinal numbers (i.e., #0,
#1, #2, etc. up to #127) for a brief period to support link-layer
retransmissions (see: Section 6.7). OAL fragment and carrier packet
formats are shown in Figure 6.
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+----------+----------------+
|OAL Header| Frag #0 |
+----------+----------------+
+----------+----------------+
|OAL Header| Frag #1 |
+----------+----------------+
+----------+----------------+
|OAL Header| Frag #2 |
+----------+----------------+
....
+----------+----------------+----+
|OAL Header| Frag #(N-1) |Csum|
+----------+----------------+----+
a) OAL fragmentation (Csum in final fragment)
+----------+-----+-----+-----+-----+-----+----+
|OAL Header| Original IP packet |Csum|
+----------+-----+-----+-----+-----+-----+----+
b) An OAL atomic fragment
+--------+----------+----------------+
|L2 Hdrs |OAL Header| Frag #i |
+--------+----------+----------------+
c) OAL carrier packet after L2 encapsulation
Figure 6: OAL Fragments and Carrier Packets
Note: the minimum MPS assumes that any middleboxes (e.g. IPv4 NATs)
that connect private networks with path MTUs smaller than 576 octets
must reassemble any fragmented (outbound) IPv4 carrier packets sent
by OAL sources before forwarding them to external Internetworks since
middleboxes that connect OAL destinations often unconditionally drop
(inbound) IPv4 fragments. However, when the path MTU in the
destination private network is small, the OAL destination itself will
be able to reassemble any IPv4 fragmentation that occurs in the
inbound path.
6.2. OAL L2 Encapsulation and Re-Encapsulation
The OAL source or intermediate node next encapsulates each OAL
fragment (with either full or compressed headers) in L2 encapsulation
headers to create a carrier packet. The OAL source or intermediate
node (i.e., the L2 source) includes a UDP header as the innermost
sublayer if NAT traversal and/or packet filtering middlebox traversal
are required; otherwise, the L2 source includes either a full or
compressed IP header and/or an actual link-layer header (e.g., such
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as for Ethernet-compatible links). The L2 source then appends any
additional encapsulation sublayer headers necessary and presents the
resulting carrier packet to an underlay interface, where the underlay
network conveys it to a next-hop OAL intermediate node or destination
(i.e., the L2 destination).
The L2 source encapsulates the OAL information immediately following
the innermost L2 sublayer header. If the first four bits of the
encapsulated OAL information following the innermost sublayer header
encode the value '6', the information must include an uncompressed
IPv6 header (plus extensions) followed by upper layer protocol
headers and data. If the first four bits encode the value '4', an
uncompressed IPv4 header (plus extensions) followed by upper layer
protocol headers and data follows. Otherwise, the first four bits
include a "Type" value, and the OAL information appears in an
alternate format as specified in Section 6.4 (Types '0' and '1' are
currently specified while all other values are reserved for future
use). Carrier packets that contain an unrecognized Type value are
unconditionally dropped.
The OAL node prepares the innermost L2 encapsulation header for OAL
packets as follows:
* For UDP encapsulation, the L2 source sets the UDP source port to
8060 (i.e., the port number reserved for AERO/OMNI). When the L2
destination is a Proxy/Server or Gateway, the L2 source sets the
UDP destination port to 8060; otherwise, the L2 source sets the
UDP destination port to its cached port number value for the peer.
The L2 source finally sets the UDP Length the same as specified in
[RFC0768]. (If the OAL packet includes an IP Jumbogram, the L2
source instead sets the UDP length to 0 and includes a Jumbo
Payload option in the L2 IP header.)
* For IP encapsulation, the L2 source sets the IP {Protocol, Next-
Header} to TBD1 (see: IANA Considerations) and sets the {Total,
Payload} Length the same as specified in [RFC0791] or [RFC8200].
(If the OAL packet includes a true Jumbogram, the L2 source
includes a Jumbo Payload option and sets {Total, Payload} Length
plus the Jumbo Payload length according to the OAL length
information.)
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* For direct encapsulations over Ethernet-compatible links, the
EtherType is set to TBD2 (see: IANA Considerations). Since the
Ethernet header does not include a length field, for the OMNI
EtherType the Ethernet header is followed by a four-octet Payload
Length field followed immediately by the encapsulated OAL
information. The Payload Length field encodes the length in
octets (in network byte order) of the OAL information exclusive of
the lengths of the Ethernet header and trailer.
When an L2 source includes a UDP header, it SHOULD calculate and
include a UDP checksum in carrier packets with full OAL headers to
prevent mis-delivery, and MAY disable UDP checksums in carrier
packets with compressed OAL headers (see: Section 6.4). If the L2
source discovers that a path is dropping carrier packets with UDP
checksums disabled, it should enable UDP checksums in future carrier
packets sent to the same L2 destination. If the L2 source discovers
that a path is dropping carrier packets that do not include a UDP
header, it should include a UDP header in future carrier packets.
When an L2 source sends carrier packets with compressed OAL headers
and with UDP checksums disabled, mis-delivery due to corruption of
the 4-octet Multilink Forwarding Vector Index (MFVI) is possible but
unlikely since the corrupted index would somehow have to match valid
state in the (sparsely-populated) Multilink Forwarding Information
Based (MFIB). In the unlikely event that a match occurs, an OAL
destination may receive a mis-delivered carrier packet but can
immediately reject packets with an incorrect Identification. If the
Identification value is somehow accepted, the OAL destination may
submit the mis-delivered carrier packet to the reassembly cache where
it will most likely be rejected due to incorrect reassembly
parameters. If a reassembly that includes the mis-delivered carrier
packets somehow succeeds (or, for atomic fragments) the OAL
destination will verify the OAL checksum to detect corruption.
Finally, any spurious data that somehow eludes all prior checks will
be detected and rejected by end-to-end upper layer integrity checks.
See: [RFC6935][RFC6936] for further discussion.
For L2 encapsulations over IP, when the L2 source is also the OAL
source it next copies the "Type of Service/Traffic Class" [RFC2983]
and "Explicit Congestion Notification (ECN)" [RFC3168] values in the
OAL header into the corresponding fields in the L2 IP header, then
(for IPv6) set the L2 IPv6 header "Flow Label" as specified in
[RFC6438]. The L2 source then sets the L2 IP TTL/Hop Limit the same
as for any host (i.e., it does not copy the Hop Limit value from the
OAL header) and finally sets the source and destination IP addresses
to direct the carrier packet to the next hop. For carrier packets
undergoing re-encapsulation, the OAL intermediate node L2 source
decrements the OAL header Hop Limit and discards the carrier packet
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if the value reaches 0. The L2 source then copies the "Type of
Service/Traffic Class" and "Explicit Congestion Notification (ECN)"
values from the previous hop L2 encapsulation header into the OAL
header (if present), then finally sets the source and destination IP
addresses the same as above.
Following L2 encapsulation/re-encapsulation, the L2 source forwards
the resulting carrier packets over one or more underlay interfaces.
The underlay interfaces often connect directly to physical media on
the local platform (e.g., a laptop computer with WiFi, etc.), but in
some configurations the physical media may be hosted on a separate
Local Area Network (LAN) node. In that case, the OMNI interface can
establish a Layer-2 VLAN or a point-to-point tunnel (at a layer below
the underlay interface) to the node hosting the physical media. The
OMNI interface may also apply encapsulation at the underlay interface
layer (e.g., as for a tunnel virtual interface) such that carrier
packets would appear "double-encapsulated" on the LAN; the node
hosting the physical media in turn removes the LAN encapsulation
prior to transmission or inserts it following reception. Finally,
the underlay interface must monitor the node hosting the physical
media (e.g., through periodic keepalives) so that it can convey
up/down/status information to the OMNI interface.
6.3. OAL L2 Decapsulation and Reassembly
When an OMNI interface receives a carrier packet from an underlay
interface, it copies the ECN value from the L2 encapsulation headers
into the OAL header if the carrier packet contains a first-fragment.
The OMNI interface next discards the L2 encapsulation headers and
examines the OAL header of the enclosed OAL fragment. If the OAL
fragment is addressed to a different node, the OMNI interface (acting
as an OAL intermediate node) re-encapsulates and forwards while
decrementing the OAL Hop Limit as discussed in Section 6.2. If the
OAL fragment is addressed to itself, the OMNI interface (acting as an
OAL destination) accepts or drops the fragment based on the (Source,
Destination, Identification)-tuple and/or integrity checks.
The OAL destination next drops all non-final OAL fragments smaller
than the minimum MPS and all fragments that would overlap or leave
"holes" smaller than the minimum MPS with respect to other fragments
already received. The OAL destination updates a checklist of
accepted fragments of the same OAL packet that include an Ordinal
number (i.e., Ordinals 0 through 127), but admits all accepted
fragments into the reassembly cache after first removing any
extension headers except for the fragment header itself. When the
OAL destination receives the final fragment (i.e., the one with More
Fragments set to 0), it caches the trailing checksum and reduces the
Payload Length by 2. When reassembly is complete, the OAL
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destination verifies the OAL packet checksum and discards the packet
if the checksum is incorrect. If the OAL packet was accepted, the
OAL destination finally removes the OAL headers and delivers the
original IP packet to the network layer.
Carrier packets often travel over paths where all links in the path
include CRC-32 integrity checks for effective hop-by-hop error
detection for payload sizes up to 9180 octets [CRC], but other paths
may traverse links (such as tunnels over IPv4) that do not include
adequate integrity protection. The OAL checksum therefore allows OAL
destinations to detect reassembly misassociation splicing errors and/
or carrier packet corruption caused by unprotected links [CKSUM].
The OAL checksum also provides algorithmic diversity with respect to
both lower layer CRCs and upper layer Internet checksums as part of a
complimentary multi-layer integrity assurance architecture. Any
corruption not detected by lower layer integrity checks is therefore
very likely to be detected by upper layer integrity checks that use
diverse algorithms.
6.4. OAL Header Compression
OAL sources that send carrier packets with full OAL headers include a
CRH-32 extension for segment-by-segment forwarding based on a
Multilink Forwarding Information Base (MFIB) in each OAL intermediate
node. OAL source, intermediate and destination nodes can instead
establish header compression state through IPv6 ND NS/NA message
exchanges. After an initial NS/NA exchange, OAL nodes can apply OAL
Header Compression to significantly reduce encapsulation overhead.
Each OAL node establishes MFIB soft state entries known as Multilink
Forwarding Vectors (MVFs) which support both carrier packet
forwarding and OAL header compression/decompression. For OAL
sources, each MFV is referenced by a single Multilink Forwarding
Vector Index (MFVI) that provides compression/decompression and
forwarding context for the next hop. For OAL destinations, the MFV
is referenced by a single MFVI that provides context for the previous
hop. For OAL intermediate nodes, the MFV is referenced by two MFVIs
- one for the previous hop and one for the next hop.
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When an OAL node forwards carrier packets to a next hop, it can
include a full OAL header with a CRH-32 extension containing one or
more MVFIs. Whenever possible, however, the OAL node should instead
omit significant portions of the OAL header (including the CRH-32)
while applying OAL header compression. The full or compressed OAL
header follows immediately after the innermost L2 encapsulation
(i.e., UDP, IP or L2) as discussed in Section 6.2. Two OAL
compressed header types (Types '0' and '1') are currently specified
below (note that the (A)RQ flag is always considered set and
therefore omitted from the compressed headers themselves).
For OAL first-fragments (including atomic fragments), the OAL node
uses OMNI Compressed Header - Type 0 (OCH-0) format as shown in
Figure 7:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Hop Limit |ECN| Parcel ID |R|X|P|S|M| Ident. (0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification (1-3) | MFVI (0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MFVI (1-3) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: OMNI Compressed Header - Type 0 (OCH-0)
The format begins with a 4-bit Type, a 6-bit Hop Limit, a 2-bit
Explicit Congestion Notification (ECN) field, a 7-bit Parcel ID and 5
flag bits. The format concludes with a 4-octet Identification field
followed (optionally) by a 4-octet MFVI field. The OAL node sets
Type to the value 0, sets Hop Limit to the minimum of the
uncompressed OAL header Hop Limit and 63, sets ECN the same as for an
uncompressed OAL header, and sets (Parcel ID, (P)arcel, (S)ub-
parcels, (M)ore Fragments, Identification) the same as for an
uncompressed fragment header. The OAL node finally sets Inde(X) and
includes an MFVI if necessary; otherwise, it clears Inde(X) and omits
the MFVI. (The (R)eserved flag is set to 0 on transmission and
ignored on reception.)
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The OAL first fragment (beginning with the original IP header) is
then included immediately following the OCH-0 header, and the L2
header length field is reduced by the difference in length between
the compressed headers and full-length OAL IPv6 and Fragment headers.
The OAL destination can therefore determine the Payload Length by
examining the L2 header length field and/or the length field(s) in
the original IP header. The OCH-0 format applies for first fragments
only, which are always regarded as ordinal fragment 0 even though no
explicit Ordinal field is included. The (A)RQ flag is always
implicitly set, and therefore omitted from the OCH-0 header.
For OAL non-first fragments (i.e., those with non-zero Fragment
Offsets), the OAL uses OMNI Compressed Header - Type 1 (OCH-1) format
as shown in Figure 8:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Hop Limit | Ordinal | Fragment Offset |X|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MFVI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: OMNI Compressed Header - Type 1 (OCH-1)
The format begins with a 4-bit Type, a 6-bit Hop Limit, a 7-bit
Ordinal, a 13-bit Fragment Offset and 2 flag bits. The format
concludes with a 4-octet Identification field followed (optionally)
by a 4-octet MFVI field. The OAL node sets Type to the value 1, sets
Hop Limit to the minimum of the uncompressed OAL header Hop Limit and
63, and sets (Ordinal, Fragment Offset, (M)ore Fragments,
Identification) the same as for an uncompressed fragment header. If
an MFVI is needed, the OAL node finally sets Inde(X) and includes an
MFVI; otherwise, the node clears Inde(X) and omits the MFVI.
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The OAL non-first fragment body is then included immediately
following the OCH-1 header, and the L2 header length field is reduced
by the difference in length between the compressed headers and full-
length OAL IPv6 and Fragment headers. The OAL destination will then
be able to determine the Payload Length by examining the L2 header
length field. The OCH-1 format applies for non-first fragments only;
therefore, the OAL source sets Ordinal to a monotonically increasing
value beginning with 1 for the first non-first fragment, 2 for the
second non-first fragment, etc., up to and including the final
fragment. If more than 127 non-first fragments are included, these
additional fragments instead set Ordinal to 0. The (A)RQ flag is
always implicitly set, and therefore omitted from the OCH-1 header.
When an OAL destination or intermediate node receives a carrier
packet, it determines the length of the encapsulated OAL information
by examining the length field of the innermost L2 header, verifies
that the innermost next header field indicates OMNI (see:
Section 6.2), then examines the first four bits immediately following
the innermost header. If the bits contain the value 4 or 6, the OAL
node processes the remainder as an uncompressed OAL/IP header. If
the bits contain a value 0 or 1, the OAL node instead processes the
remainder of the header as an OCH-0/1 as specified above.
For carrier packets with OCH or full OAL headers addressed to itself
and with CRH-32 extensions, the OAL node then uses the MFVI to locate
the cached MFV which determines the next hop. During forwarding, the
OAL node changes the MFVI to the cached value for the MVF next hop.
If the OAL node is the destination, it instead reconstructs the full
OAL headers then adds the resulting OAL fragment to the reassembly
cache if the Identification is acceptable. (Note that for carrier
packets that include an OCH-0 with both the X and M flags set to 0,
the OAL node can instead locate forwarding state by examining the
original IP packet header information that appears immediately after
the OCH-0 header.)
Note: OAL header compression does not interfere with checksum
calculation and verification, which must be applied according to the
full OAL pseudo-header per Section 6.1 even when compression is used.
Note: The OCH-0/1 formats do not include the Traffic Class and Flow
Label information that appears in uncompressed OAL IPv6 headers.
Therefore, when OAL header compression state is initialized the
Traffic Class and Flow Label are considered fixed for as long as the
flow uses OCH-0/1 headers. If the flow requires frequent changes to
Traffic Class and/or Flow Label information, it can include
uncompressed OAL headers either continuously or periodically to
update header compression state.
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6.5. OAL-in-OAL Encapsulation
When an OAL source is unable to forward carrier packets directly to
an OAL destination without "tunneling" through a pair of OAL
intermediate nodes, the OAL source must regard the intermediate nodes
as ingress and egress tunnel endpoints. This will result in nested
OAL-in-OAL encapsulation in which the OAL source performs
fragmentation on the inner OAL packet then forwards the fragments to
the ingress tunnel endpoint which encapsulates each resulting OAL
fragment in an additional OAL header before performing fragmentation
following encapsulation.
For example, if the OAL source has an NCE for the OAL destination
with MFVI 0x2376a7b5 and Identification 0x12345678 and the OAL
ingress tunnel endpoint has an NCE for the OAL egress tunnel endpoint
with MFVI 0xacdebf12 and Identification 0x98765432, the OAL source
prepares the carrier packets using compressed/uncompressed OAL
headers that include the MFVI and Identification corresponding to the
OAL destination and with L2 header information addressed to the next
hop toward the ingress tunnel endpoint. When the ingress tunnel
endpoint receives the carrier packet, it recognizes the current MFVI
included by the OAL source and determines the correct next hop MFVI.
The ingress tunnel endpoint then discards the L2 headers from the
previous hop and encapsulates the original compressed/uncompressed
OAL header within a second compressed/uncompressed OAL header while
including the next-hop MVFI in the outer OAL encapsulation header and
omitting the MFVI in the inner header. The ingress tunnel endpoint
then includes L2 encapsulation headers with destinations appropriate
for the next hop on the path to the egress tunnel endpoint. The
encapsulation appears as shown in Figure 9:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L2 headers (previous hop) | | L2 headers (next hop) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Original OAL/OCH Hdr | | Encapsulation OAL/OCH Hdr |
| Id=0x12345678 | | Id=0x98765432 |
| MFVI=0x2376a7b5 | | MFVI=0xacdebf12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | Original OAL/OCH Hdr |
| | | Id=0x12345678 |
| Carrier packet data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Carrier packet data |
| Original OAL Checksum | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
Original Carrier packet +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
from OAL source | Original OAL Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encapsulation OAL Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Carrier packet following OAL ingress
(re)encapsulation before fragmentation
Figure 9: Carrier Packet in Carrier Packet Encapsulation
Note that only a single OAL-in-OAL encapsulation layer is supported,
and that MFVIs appear only in the outer OAL header (i.e., either
within a CRH-32 routing header when a full OAL header is used or
within an OCH header with X set to 0). The inner OAL header should
omit the CRH-32 header or use an OCH header with X set to 1,
respectively.
Note that OAL/OCH encapsulation may cause the payloads of OAL packets
produced by the ingress tunnel endpoint to exceed the minimum MPS by
a small amount. If the ingress has assurance that the path to the
egress will include only links capable of transiting the resulting
(slightly larger) carrier packets it should forward without further
fragmentation. Otherwise, the ingress must perform fragmentation
following encapsulation to produce two fragments such that the size
of the first fragment matches the size of the original OAL packet,
and with the remainder in a second fragment. The egress tunnel
endpoint must then reassemble then decapsulate to arrive at the
original OAL packet which is then subject to further forwarding.
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6.6. OAL Identification Window Maintenance
The OAL encapsulates each original IP packet as an OAL packet then
performs fragmentation to produce one or more carrier packets with
the same 32-bit Identification value. In environments where spoofing
is not considered a threat, OMNI interfaces send OAL packets with
Identifications beginning with an unpredictable Initial Send Sequence
(ISS) value [RFC7739] monotonically incremented (modulo 2**32) for
each successive OAL packet sent to either a specific neighbor or to
any neighbor. (The OMNI interface may later change to a new
unpredictable ISS value as long as the Identifications are assured
unique within a timeframe that would prevent the fragments of a first
OAL packet from becoming associated with the reassembly of a second
OAL packet.) In other environments, OMNI interfaces should maintain
explicit per-neighbor send and receive windows to detect and exclude
spurious carrier packets that might clutter the reassembly cache as
discussed below.
OMNI interface neighbors use TCP-like synchronization to maintain
windows with unpredictable ISS values incremented (modulo 2**32) for
each successive OAL packet and re-negotiate windows often enough to
maintain an unpredictable profile. OMNI interface neighbors exchange
IPv6 ND messages with OMNI options that include TCP-like information
fields to manage streams of OAL packets instead of streams of octets.
As a link-layer service, the OAL provides low-persistence best-effort
retransmission with no mitigations for duplication, reordering or
deterministic delivery. Since the service model is best-effort and
only control message sequence numbers are acknowledged, OAL nodes can
select unpredictable new initial sequence numbers outside of the
current window without delaying for the Maximum Segment Lifetime
(MSL).
OMNI interface neighbors maintain current and previous window state
in IPv6 ND neighbor cache entries (NCEs) to support dynamic rollover
to a new window while still sending OAL packets and accepting carrier
packets from the previous windows. Each NCE is indexed by the
neighbor's ULA, while the OAL encapsulation ULA (which may be
different) provides context for Identification verification. OMNI
interface neighbors synchronize windows through asymmetric and/or
symmetric IPv6 ND message exchanges. When a node receives an IPv6 ND
message with new window information, it resets the previous window
state based on the current window then resets the current window
based on new and/or pending information.
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The IPv6 ND message OMNI option header extension sub-option includes
TCP-like information fields including Sequence Number,
Acknowledgement Number, Window and flags (see: Section 12). OMNI
interface neighbors maintain the following TCP-like state variables
in the NCE:
Send Sequence Variables (current, previous and pending)
SND.NXT - send next
SND.WND - send window
ISS - initial send sequence number
Receive Sequence Variables (current and previous)
RCV.NXT - receive next
RCV.WND - receive window
IRS - initial receive sequence number
OMNI interface neighbors "OAL A" and "OAL B" exchange IPv6 ND
messages per [RFC4861] with OMNI options that include TCP-like
information fields. When OAL A synchronizes with OAL B, it maintains
both a current and previous SND.WND beginning with a new
unpredictable ISS and monotonically increments SND.NXT for each
successive OAL packet transmission. OAL A initiates synchronization
by including the new ISS in the Sequence Number of an authentic IPv6
ND message with the SYN flag set and with Window set to M (up to
2**24) as a tentative receive window size while creating a NCE in the
INCOMPLETE state if necessary. OAL A caches the new ISS as pending,
uses the new ISS as the Identification for OAL encapsulation, then
sends the resulting OAL packet to OAL B and waits up to RetransTimer
milliseconds to receive an IPv6 ND message response with the ACK flag
set (retransmitting up to MAX_UNICAST_SOLICIT times if necessary).
When OAL B receives the SYN, it creates a NCE in the STALE state if
necessary, resets its RCV variables, caches the tentative (send)
window size M, and selects a (receive) window size N (up to 2**24) to
indicate the number of OAL packets it is willing to accept under the
current RCV.WND. (The RCV.WND should be large enough to minimize
control message overhead yet small enough to provide an effective
filter for spurious carrier packets.) OAL B then prepares an IPv6 ND
message with the ACK flag set, with the Acknowledgement Number set to
OAL A's next sequence number, and with Window set to N. Since OAL B
does not assert an ISS of its own, it uses the IRS it has cached for
OAL A as the Identification for OAL encapsulation then sends the ACK
to OAL A.
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When OAL A receives the ACK, it notes that the Identification in the
OAL header matches its pending ISS. OAL A then sets the NCE state to
REACHABLE and resets its SND variables based on the Window size and
Acknowledgement Number (which must include the sequence number
following the pending ISS). OAL A can then begin sending OAL packets
to OAL B with Identification values within the (new) current SND.WND
for up to ReachableTime milliseconds or until the NCE is updated by a
new IPv6 ND message exchange. This implies that OAL A must send a
new SYN before sending more than N OAL packets within the current
SND.WND, i.e., even if ReachableTime is not nearing expiration.
After OAL B returns the ACK, it accepts carrier packets received from
OAL A within either the current or previous RCV.WND as well as any
new authentic NS/RS SYN messages received from OAL A even if outside
the windows.
OMNI interface neighbors can employ asymmetric window synchronization
as described above using two independent (SYN -> ACK) exchanges
(i.e., a four-message exchange), or they can employ symmetric window
synchronization using a modified version of the TCP three-way
handshake as follows:
* OAL A prepares a SYN with an unpredictable ISS not within the
current SND.WND and with Window set to M as a tentative receive
window size. OAL A caches the new ISS and Window size as pending
information, uses the pending ISS as the Identification for OAL
encapsulation, then sends the resulting OAL packet to OAL B and
waits up to RetransTimer milliseconds to receive an ACK response
(retransmitting up to MAX_UNICAST_SOLICIT times if necessary).
* OAL B receives the SYN, then resets its RCV variables based on the
Sequence Number while caching OAL A's tentative receive Window
size M and a new unpredictable ISS outside of its current window
as pending information. OAL B then prepares a response with
Sequence Number set to the pending ISS and Acknowledgement Number
set to OAL A's next sequence number. OAL B then sets both the SYN
and ACK flags, sets Window to N and sets the OPT flag according to
whether an explicit concluding ACK is optional or mandatory. OAL
B then uses the pending ISS as the Identification for OAL
encapsulation, sends the resulting OAL packet to OAL A and waits
up to RetransTimer milliseconds to receive an acknowledgement
(retransmitting up to MAX_UNICAST_SOLICIT times if necessary).
* OAL A receives the SYN/ACK, then resets its SND variables based on
the Acknowledgement Number (which must include the sequence number
following the pending ISS) and OAL B's advertised Window N. OAL A
then resets its RCV variables based on the Sequence Number and
marks the NCE as REACHABLE. If the OPT flag is clear, OAL A next
prepares an immediate solicited NA message with the ACK flag set,
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the Acknowledgement Number set to OAL B's next sequence number,
with Window set a value that may be the same as or different than
M, and with the OAL encapsulation Identification to SND.NXT, then
sends the resulting OAL packet to OAL B. If the OPT flag is set
and OAL A has OAL packets queued to send to OAL B, it can
optionally begin sending their carrier packets under the (new)
current SND.WND as implicit acknowledgements instead of returning
an explicit ACK. In that case, the tentative Window size M
becomes the current receive window size.
* OAL B receives the implicit/explicit acknowledgement(s) then
resets its SND state based on the pending/advertised values and
marks the NCE as REACHABLE. If OAL B receives an explicit
acknowledgement, it uses the advertised Window size and abandons
the tentative size. (Note that OAL B sets the OPT flag in the
SYN/ACK to assert that it will interpret timely receipt of carrier
packets within the (new) current window as an implicit
acknowledgement. Potential benefits include reduced delays and
control message overhead, but use case analysis is outside the
scope of this specification.)
Following synchronization, OAL A and OAL B hold updated NCEs and can
exchange OAL packets with Identifications set to SND.NXT while the
state remains REACHABLE and there is available window capacity.
Either neighbor may at any time send a new SYN to assert a new ISS.
For example, if OAL A's current SND.WND for OAL B is nearing
exhaustion and/or ReachableTime is nearing expiration, OAL A
continues to send OAL packets under the current SND.WND while also
sending a SYN with a new unpredictable ISS. When OAL B receives the
SYN, it resets its RCV variables and may optionally return either an
asymmetric ACK or a symmetric SYN/ACK to also assert a new ISS.
While sending SYNs, both neighbors continue to send OAL packets with
Identifications set to the current SND.NXT then reset the SND
variables after an acknowledgement is received.
While the optimal symmetric exchange is efficient, anomalous
conditions such as receipt of old duplicate SYNs can cause confusion
for the algorithm as discussed in Section 3.4 of [RFC0793]. For this
reason, the OMNI option header includes an RST flag which OAL nodes
set in solicited NA responses to ACKs received with incorrect
acknowledgement numbers. The RST procedures (and subsequent
synchronization recovery) are conducted exactly as specified in
[RFC0793].
OMNI interfaces may set the PNG ("ping") flag when a reachability
confirmation outside the context of the IPv6 ND protocol is needed
(OMNI interfaces therefore most often set the PNG flag in
advertisement messages and ignore it in solicitation messages). When
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an OMNI interface receives a PNG, it returns an unsolicited NA (uNA)
ACK with the PNG message Identification in the Acknowledgment, but
without updating RCV state variables. OMNI interfaces return unicast
uNA ACKs even for multicast PNG destination addresses, since OMNI
link multicast is based on unicast emulation.
OMNI interfaces that employ the window synchronization procedures
described above observe the following requirements:
* OMNI interfaces MUST select new unpredictable ISS values that are
at least a full window outside of the current SND.WND.
* OMNI interfaces MUST set the initial SYN message Window field to a
tentative value to be used only if no concluding NA ACK is sent.
* OMNI interfaces that receive advertisements with the PNG and/or
SYN flag set MUST NOT set the PNG and/or SYN flag in uNA
responses.
* OMNI interfaces that send advertisements with the PNG and/or SYN
flag set MUST ignore uNA responses with the PNG and/or SYN flag
set.
* OMNI interfaces MUST send IPv6 ND messages used for window
synchronization securely while using unpredictable initial
Identification values until synchronization is complete.
Note: Although OMNI interfaces employ TCP-like window synchronization
and support uNA ACK responses to SYNs and PNGs, all other aspects of
the IPv6 ND protocol (e.g., control message exchanges, NCE state
management, timers, retransmission limits, etc.) are honored exactly
per [RFC4861].
Note: Recipients of OAL-encapsulated IPv6 ND messages index the NCE
based on the message source address, which also determines the
carrier packet Identification window. However, IPv6 ND messages may
contain a message source address that does not match the OMNI
encapsulation source address when the recipient acts as a proxy.
Note: OMNI interface neighbors apply the same send and receive
windows for all of their (multilink) underlay interface pairs that
exchange carrier packets. Each interface pair represents a distinct
underlay network path, and the set of paths traversed may be highly
diverse when multiple interface pairs are used. OMNI intermediate
nodes therefore SHOULD NOT cache window synchronization parameters in
IPv6 ND messages they forward since there is no way to ensure
network-wide middlebox state consistency.
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6.7. OAL Fragment Retransmission
When the OAL source sends carrier packets to an OAL destination, it
should cache recently sent packets in case timely best-effort
selective retransmission is requested. The OAL destination in turn
maintains a checklist for the (Source, Destination, Identification)-
tuple of recently received carrier packets and notes the ordinal
numbers of OAL packet fragments already received (i.e., as Frag #0,
Frag #1, Frag #2, etc.). The timeframe for maintaining the OAL
source and destination caches determines the link persistence (see:
[RFC3366]).
If the OAL destination notices some fragments missing after most
other fragments within the same link persistence timeframe have
already arrived, it may issue an Automatic Repeat Request (ARQ) with
Selective Repeat (SR) by sending a uNA message to the OAL source.
The OAL destination creates a uNA message with an OMNI option with
one or more Fragmentation Report (FRAGREP) sub-options that include a
list of (Identification, Bitmap)-tuples for fragments received and
missing from this OAL source (see: Section 12 and
[I-D.templin-6man-fragrep]). The OAL destination includes an
authentication signature if necessary, performs OAL encapsulation
(with the its own address as the OAL source and the source address of
the message that prompted the uNA as the OAL destination) and sends
the message to the OAL source.
When the OAL source receives the uNA message, it authenticates the
message then examines the FRAGREP. For each (Source, Destination,
Identification)-tuple, the OAL source determines whether it still
holds the corresponding carrier packets in its cache and retransmits
any for which the Bitmap indicates a loss event. For example, if the
Bitmap indicates that ordinal fragments #3, #7, #10 and #13 from the
OAL packet with Identification 0x12345678 are missing the OAL source
only retransmits carrier packets containing those fragments. When
the OAL destination receives the retransmitted carrier packets, it
admits the enclosed fragments into the reassembly cache and updates
its checklist. If some fragments are still missing, the OAL
destination may send a small number of additional uNA ARQ/SRs within
the link persistence timeframe.
The OAL therefore provides a link-layer low-to-medium persistence
ARQ/SR service consistent with [RFC3366] and Section 8.1 of
[RFC3819]. The service provides the benefit of timely best-effort
link-layer retransmissions which may reduce packet loss and avoid
some unnecessary end-to-end delays. This best-effort network-based
service therefore compliments higher layer end-to-end protocols
responsible for true reliability.
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6.8. OAL MTU Feedback Messaging
When the OMNI interface forwards original IP packets from the network
layer, it invokes the OAL and returns internally-generated ICMPv4
Fragmentation Needed [RFC1191] or ICMPv6 Path MTU Discovery (PMTUD)
Packet Too Big (PTB) [RFC8201] messages as necessary. This document
refers to both of these ICMPv4/ICMPv6 message types simply as "PTBs",
and introduces a distinction between PTB "hard" and "soft" errors as
discussed below and also in [I-D.templin-6man-fragrep].
Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6
header Code field value 0 are hard errors that always indicate that a
packet has been dropped due to a real MTU restriction. However, the
OMNI interface can also forward large original IP packets via OAL
encapsulation and fragmentation while at the same time returning PTB
soft error messages (subject to rate limiting) if it deems the
original IP packet too large according to factors such as link
performance characteristics, number of fragments needed, reassembly
congestion, etc. This ensures that the path MTU is adaptive and
reflects the current path used for a given data flow. The OMNI
interface can therefore continuously forward packets without loss
while returning PTB soft error messages recommending a smaller size
if necessary. Original sources that receive the soft errors in turn
reduce the size of the packets they send (i.e., the same as for hard
errors), but can soon resume sending larger packets if the soft
errors subside.
An OAL source sends PTB soft error messages by setting the ICMPv4
header "unused" field or ICMPv6 header Code field to the value 1 if
the packet was dropped or 2 if the packet was forwarded successfully.
The OAL source sets the PTB destination address to the original IP
packet source, and sets the source address to one of its OMNI
interface addresses that is routable from the perspective of the
original source. The OAL source then sets the MTU field to a value
smaller than the original packet size but no smaller than 576 for
ICMPv4 or 1280 for ICMPv6, writes the leading portion of the original
IP packet first fragment into the "packet in error" field, and
returns the PTB soft error to the original source. When the original
source receives the PTB soft error, it temporarily reduces the size
of the packets it sends the same as for hard errors but may seek to
increase future packet sizes dynamically while no further soft errors
are arriving. (If the original source does not recognize the soft
error code, it regards the PTB the same as a hard error but should
heed the retransmission advice given in [RFC8201] suggesting
retransmission based on normal packetization layer retransmission
timers.)
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An OAL destination may experience reassembly cache congestion, and
can return uNA messages to the OAL source that originated the
fragments (subject to rate limiting) that include OMNI encapsulated
PTB messages with code 1 or 2. The OAL destination creates a uNA
message with an OMNI option containing an authentication message sub-
option if necessary followed optionally by a ICMPv6 Error sub-option
that encodes a PTB message with a reduced value and with the leading
portion an OAL first fragment containing the header of an original IP
packet whose source must be notified (see: Section 12). The OAL
destination encapsulates the leading portion of the OAL first
fragment (beginning with the OAL header) in the PTB "packet in error"
field, signs the message if an authentication sub-option is included,
performs OAL encapsulation (with the its own address as the OAL
source and the source address of the message that prompted the uNA as
the OAL destination) and sends the message to the OAL source.
When the OAL source receives the uNA message, it sends a
corresponding network layer PTB soft error to the original source to
recommend a smaller size. The OAL source crafts the PTB by
extracting the leading portion of the original IP packet from the
OMNI encapsulated PTB message (i.e., not including the OAL header)
and writes it in the "packet in error" field of a network layer PTB
with destination set to the original IP packet source and source set
to one of its OMNI interface addresses that is routable from the
perspective of the original source.
Original sources that receive PTB soft errors can dynamically tune
the size of the original IP packets they to send to produce the best
possible throughput and latency, with the understanding that these
parameters may change over time due to factors such as congestion,
mobility, network path changes, etc. The receipt or absence of soft
errors should be seen as hints of when increasing or decreasing
packet sizes may be beneficial. The OMNI interface supports
continuous transmission and reception of packets of various sizes in
the face of dynamically changing network conditions. Moreover, since
PTB soft errors do not indicate a hard limit, original sources that
receive soft errors can resume sending larger packets without waiting
for the recommended 10 minutes specified for PTB hard errors
[RFC1191][RFC8201]. The OMNI interface therefore provides an
adaptive service that accommodates MTU diversity especially well-
suited for dynamic multilink environments.
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6.9. OAL Super-Packets
By default, the OAL source includes a 40-octet IPv6 encapsulation
header for each original IP packet during OAL encapsulation. The OAL
source also calculates then performs fragmentation such that a copy
of the 40-octet IPv6 header plus an 8-octet IPv6 Fragment Header is
included in each OAL fragment (when a Routing Header is added, the
OAL encapsulation headers become larger still). However, these
encapsulations may represent excessive overhead in some environments.
OAL header compression can dramatically reduce the amount of
encapsulation overhead, however a complimentary technique known as
"packing" (see: [I-D.ietf-intarea-tunnels]) supports encapsulation of
multiple original IP packets and/or control messages within a single
OAL "super-packet".
When the OAL source has multiple original IP packets to send to the
same OAL destination with total length no larger than the OAL
destination MRU, it can concatenate them into a super-packet
encapsulated in a single OAL header. Within the OAL super-packet,
the IP header of the first original IP packet (iHa) followed by its
data (iDa) is concatenated immediately following the OAL header, then
the IP header of the next original packet (iHb) followed by its data
(iDb) is concatenated immediately following the first original
packet, etc. with a trailing checksum field included in the final
fragment. The OAL super-packet format is transposed from
[I-D.ietf-intarea-tunnels] and shown in Figure 10:
<------- Original IP packets ------->
+-----+-----+
| iHa | iDa |
+-----+-----+
|
| +-----+-----+
| | iHb | iDb |
| +-----+-----+
| |
| | +-----+-----+
| | | iHc | iDc |
| | +-----+-----+
| | |
v v v
+----------+-----+-----+-----+-----+-----+-----+----+
| OAL Hdr | iHa | iDa | iHb | iDb | iHc | iDc |Csum|
+----------+-----+-----+-----+-----+-----+-----+----+
<--- OAL "Super-Packet" with single OAL Hdr/Csum --->
Figure 10: OAL Super-Packet Format
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When the OAL source prepares a super-packet, it applies OAL
fragmentation, includes a trailing checksum in the final fragment,
applies L2 encapsulation to each fragment then sends the resulting
carrier packets to the OAL destination. When the OAL destination
receives the super-packet it sets aside the trailing checksum,
reassembles if necessary, then verifies the checksum while regarding
the remaining OAL header Payload Length as the sum of the lengths of
all payload packets. The OAL destination then selectively extracts
each original IP packet (e.g., by setting pointers into the super-
packet buffer and maintaining a reference count, by copying each
packet into a separate buffer, etc.) and forwards each packet to the
network layer. During extraction, the OAL determines the IP protocol
version of each successive original IP packet 'j' by examining the
four most-significant bits of iH(j), and determines the length of the
packet by examining the rest of iH(j) according to the IP protocol
version.
When an OAL source prepares a super-packet that includes an IPv6 ND
message with an authentication signature or ICMPv6 message checksum
as the first original IP packet (i.e., iHa/iDa), it calculates the
authentication signature or checksum over the remainder of super-
packet. Security and integrity for forwarding initial protocol data
packets in conjunction with IPv6 ND messages used to establish NCE
state are therefore supported. (A common use case entails a path MPS
probe beginning with a signed IPv6 ND message followed by a NULL IPv6
packet with a suitably large (Jumbo) Payload Length but with Next
Header set to 59 for "No Next Header".)
6.10. OAL Bubbles
OAL sources may send NULL OAL packets known as "bubbles" for the
purpose of establishing Network Address Translator (NAT) state on the
path to the OAL destination. The OAL source prepares a bubble by
crafting an OAL header with appropriate IPv6 source and destination
ULAs, with the IPv6 Next Header field set to the value 59 ("No Next
Header" - see [RFC8200]) and with only the trailing OAL Checksum
field (i.e., and no protocol data) immediately following the IPv6
header.
The OAL source includes a random Identification value then
encapsulates the OAL packet in L2 headers destined to either the
mapped address of the OAL destination's first-hop ingress NAT or the
L2 address of the OAL destination itself. When the OAL source sends
the resulting carrier packet, any egress NATs in the path toward the
L2 destination will establish state based on the activity but the
bubble will be harmlessly discarded by either an ingress NAT on the
path to the OAL destination or by the OAL destination itself.
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The bubble concept for establishing NAT state originated in [RFC4380]
and was later updated by [RFC6081]. OAL bubbles may be employed by
mobility services such as [I-D.templin-6man-aero].
6.11. OAL Requirements
In light of the above, OAL sources, destinations and intermediate
nodes observe the following normative requirements:
* OAL sources MUST forward original IP packets either larger than
the OMNI interface MRU or smaller than the minimum MPS minus the
trailing checksum size as atomic fragments (i.e., and not as
multiple fragments).
* OAL sources MUST produce non-final fragments with payloads no
smaller than the minimum MPS during fragmentation.
* OAL intermediate nodes SHOULD and OAL destinations MUST
unconditionally drop any non-final OAL fragments with payloads
smaller than the minimum MPS.
* OAL destinations MUST drop any new OAL fragments with offset and
length that would overlap with other fragments and/or leave holes
smaller than the minimum MPS between fragments that have already
been received.
Note: Under the minimum MPS, ordinary 1500 octet original IP packets
would require at most 4 OAL fragments, with each non-final fragment
containing 400 payload octets and the final fragment containing 302
payload octets (i.e., the final 300 octets of the original IP packet
plus the 2 octet trailing checksum). For all packet sizes, the
likelihood of successful reassembly may improve when the OMNI
interface sends all fragments of the same fragmented OAL packet
consecutively over the same underlay interface pair instead of spread
across multiple underlay interface pairs. Finally, an assured
minimum/path MPS allows continuous operation over all paths including
those that traverse bridged L2 media with dissimilar MTUs.
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Note: Certain legacy network hardware of the past millennium was
unable to accept packet "bursts" resulting from an IP fragmentation
event - even to the point that the hardware would reset itself when
presented with a burst. This does not seem to be a common problem in
the modern era, where fragmentation and reassembly can be readily
demonstrated at line rate (e.g., using tools such as 'iperf3') even
over fast links on ordinary hardware platforms. Even so, while the
OAL destination is reporting reassembly congestion (see: Section 6.8)
the OAL source could impose "pacing" by inserting an inter-fragment
delay and increasing or decreasing the delay according to congestion
indications.
6.12. OAL Fragmentation Security Implications
As discussed in Section 3.7 of [RFC8900], there are four basic
threats concerning IPv6 fragmentation; each of which is addressed by
effective mitigations as follows:
1. Overlapping fragment attacks - reassembly of overlapping
fragments is forbidden by [RFC8200]; therefore, this threat does
not apply to the OAL.
2. Resource exhaustion attacks - this threat is mitigated by
providing a sufficiently large OAL reassembly cache and
instituting "fast discard" of incomplete reassemblies that may be
part of a buffer exhaustion attack. The reassembly cache should
be sufficiently large so that a sustained attack does not cause
excessive loss of good reassemblies but not so large that (timer-
based) data structure management becomes computationally
expensive. The cache should also be indexed based on the arrival
underlay interface such that congestion experienced over a first
underlay interface does not cause discard of incomplete
reassemblies for uncongested underlay interfaces.
3. Attacks based on predictable fragment identification values - in
environments where spoofing is possible, this threat is mitigated
through the use of Identification windows beginning with
unpredictable values per Section 6.6. By maintaining windows of
acceptable Identifications, OAL neighbors can quickly discard
spurious carrier packets that might otherwise clutter the
reassembly cache. The OAL additionally provides an integrity
check to detect corruption that may be caused by spurious
fragments received with in-window Identification values.
4. Evasion of Network Intrusion Detection Systems (NIDS) - since the
OAL source employs a robust MPS, network-based firewalls can
inspect and drop OAL fragments containing malicious data thereby
disabling reassembly by the OAL destination. However, since OAL
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fragments may take different paths through the network (some of
which may not employ a firewall) each OAL destination must also
employ a firewall.
IPv4 includes a 16-bit Identification (IP ID) field with only 65535
unique values such that at high data rates the field could wrap and
apply to new carrier packets while the fragments of old packets using
the same IP ID are still alive in the network [RFC4963]. Since
carrier packets sent via an IPv4 path with DF=0 are normally no
larger than 576 octets, IPv4 fragmentation is possible only at small-
MTU links in the path which should support data rates low enough for
safe reassembly [RFC3819]. (IPv4 carrier packets larger than 576
octets with DF=0 may incur high data rate reassembly errors in the
path, but the OAL checksum provides OAL destination integrity
assurance.) Since IPv6 provides a 32-bit Identification value, IP ID
wraparound at high data rates is not a concern for IPv6
fragmentation.
Fragmentation security concerns for large IPv6 ND messages are
documented in [RFC6980]. These concerns are addressed when the OMNI
interface employs the OAL instead of directly fragmenting the IPv6 ND
message itself. For this reason, OMNI interfaces MUST NOT send IPv6
ND messages larger than the OMNI interface MTU, and MUST employ OAL
encapsulation and fragmentation for IPv6 ND messages larger than the
minimum/path MPS for this OAL destination.
Unless the path is secured at the network-layer or below (i.e., in
environments where spoofing is possible), OMNI interfaces MUST NOT
send ordinary carrier packets with Identification values outside the
current window and MUST secure IPv6 ND messages used for address
resolution or window state synchronization. OAL destinations SHOULD
therefore discard without reassembling any out-of-window OAL
fragments received over an unsecured path.
6.13. OMNI Hosts
OMNI Hosts are end systems that extend the OMNI link over ENET
underlay interfaces (i.e., either as an OMNI interface or as a
sublayer of the ENET interface itself). Each ENET is connected to
the rest of the OMNI link by a Client that receives an MNP
delegation. Clients delegate MNP addresses and/or sub-prefixes to
ENET nodes (i.e., Hosts, other Clients, routers and non-OMNI hosts)
using standard mechanisms such as DHCP [RFC8415][RFC2131] and IPv6
Stateless Address AutoConfiguration (SLAAC) [RFC4862]. Clients
forward packets between their ENET Hosts and peers on external
networks acting as routers and/or OAL intermediate nodes.
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OMNI Hosts coordinate with Clients and/or other Hosts connected to
the same ENET using IP-encapsulated IPv6 ND messages. The IP
encapsulation headers and ND messages both use the MNP-based
addresses assigned to ENET underlay interfaces as source and
destination addresses (i.e., instead of ULAs). For IPv4 MNPs, the ND
messages use IPv4-Compatible IPv6 addresses [RFC4291] in place of the
IPv4 addresses. (Note that IPv4-Compatible IPv6 addresses are
deprecated for all other uses by the aforementioned standard.)
Hosts discover Clients by sending encapsulated RS messages using an
OMNI link IP anycast address (or the unicast address of the Client)
as the RS L2 encapsulation destination as specified in Section 15.
The Client configures the IPv4 and/or IPv6 anycast addresses for the
OMNI link on its ENET interface and advertises the address(es) into
the ENET routing system. The Client then responds to the
encapsulated RS messages by sending an encapsulated RA message that
uses its ENET unicast address as the source. (To differentiate
itself from an INET border Proxy/Server, the Client sets the RA
message OMNI Interface Attributes sub-option LHS field to 0 for the
Host's interface index. When the RS message includes an L2 anycast
destination address, the Client also includes an Interface Attributes
sub-option for interface index 0 to inform the Host of its L2 unicast
address - see: Section 15 for full details on the RS and RA message
contents.)
Hosts coordinate with peer Hosts on the same ENET by sending
encapsulated NS messages to receive an NA reply. (Hosts determine
whether a peer is on the same ENET by matching the peer's IP address
with the MNP (sub)-prefix for the ENET advertised in the Client's RA
message [RFC8028].) Each ENET peer then creates a NCE and
synchronizes Identification windows the same as for OMNI link
neighbors, and the Host can then engage in OMNI link transactions
with the Client and/or other ENET Hosts. By coordinating with the
Client in this way, the Host treats the Client as if it were an ANET
Proxy/Server, and the Client provides the same services that a Proxy/
Server would provide. By coordinating with other Hosts, the peer
hosts can exchange large IP packets or parcels over the ENET using
IPv6 fragmentation if necessary.
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When a Host prepares an IP packet or parcel, it uses the IP address
of its native ENET interface as the source and the IP address of the
(remote) peer as the destination. The Host next performs parcel
segmentation if necessary (see: Section 6.14) then encapsulates the
packet/parcel in an IP header of the version supported by the ENET
while setting the source to the same address and destination to
either the same address if the peer is on the local ENET, or to the
IP address of the Client otherwise. The Host can then proceed to
exchange packets/parcels with the destination, either directly or via
the Client as an intermediate node.
The encapsulation procedures are coordinated per Section 6.1, except
that the IP encapsulation header version matches the native ENET IP
protocol version and uses IPv6 GUA or public/private IPv4 addresses
instead of ULAs. The Host sets the encapsulation IP header
{Protocol, Next-Header} field to TBD1 to indicate that this is an OAL
encapsulation and not an ordinary IP-in-IP encapsulation. When the
inner header is IPv4-based, the Host next translates the
encapsulation header into an IPv6 header with IPv4-Compatible
addresses while setting the [IPv6 Traffic Class, Payload Length, Next
Header, Hop Limit] fields according to the IPv4 {Type of Service,
Total Length, Protocol, TTL} fields, respectively, while setting Flow
Label to 0. The Host then calculates an OAL checksum, writes the
value as the final two octets of the encapsulated packet then applies
IPv6 fragmentation to the encapsulated packet to produce IPv6
fragments no smaller than the MPS the same as described in
Section 6.1. If the original encapsulation IP header was IPv4, the
Host next translates the IPv6 encapsulation headers back to IPv4
headers with Protocol value set to 44 since the immediately next
header is the IPv6 Fragment Header. The Host finally sends the IP
encapsulated fragments to the ENET peer.
When the ENET peer receives IP encapsulated fragments, for IPv4 it
first translates the encapsulation headers back to IPv6 headers with
IPv4-Compatible addresses the same as above. The peer then
reassembles and verifies the OAL checksum. If the checksum is
correct, the peer next removes the encapsulation headers and applies
parcel reassembly if necessary. The peer then either delivers the
encapsulated packet/parcel to upper layers if the peer is the
destination or forwards the packet/parcel toward the final
destination if the peer is a Client acting as an intermediate node.
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Hosts and Clients that initiate OMNI-based packet/parcel transactions
should first test the path toward the final destination using the
parcel path qualification procedure specified in
[I-D.templin-intarea-parcels]. An OMNI Host that sends and receives
parcels need not implement the full OMNI interface abstraction but
MUST implement enough of the OAL to be capable of fragmenting and
reassembling maximum-length encapsulated IP packets/parcels and sub-
parcels as discussed above and in the following section.
6.14. IP Parcels
IP parcels are specified in [I-D.templin-intarea-parcels], while
details for their application over OMNI interfaces is specified here.
IP parcels are formed by an OMNI Host or Client upper layer protocol
entity (identified by the "5-tuple" source IP address/port number,
destination IP address/port number and protocol number) when it
produces a protocol data unit containing the concatenation of up to
64 upper layer protocol segments. All non-final segments MUST be
equal in length while the final segment MUST NOT be larger but MAY be
smaller. Each non-final segment MUST be no larger than 65535 minus
the length of the IP header plus extensions, minus the length of the
OAL encapsulation header and trailer. The upper layer protocol then
presents the buffer and non-final segment size to the IP layer which
appends a single IP header (plus any extension headers) before
presenting the parcel to the OMNI Interface.
For IPv4, the IP layer prepares the parcel by appending an IPv4
header with a Jumbo Payload option (see: Section 5.1) where "Jumbo
Payload Length" is a 32-bit unsigned integer value (in network byte
order) set to the lengths of the IPv4 header plus all concatenated
segments. The IP layer next sets the IPv4 header DF bit to 1, then
sets the IPv4 header Total Length field to the length of the IPv4
header plus the length of the first segment only. (Note: the IP
layer can form true IPv4 jumbograms (as opposed to parcels) by
instead setting the Total Length field to the length of the IPv4
header only.)
For IPv6, the IP layer forms a parcel by appending an IPv6 header
with a Jumbo Payload option the same as for IPv4 above where "Jumbo
Payload Length" is set to the lengths of the IPv6 Hop-by-Hop Options
header and any other extension headers present plus all concatenated
segments. The IP layer next sets the IPv6 header Payload Length
field to the lengths of the IPv6 Hop-by-Hop Options header and any
other extension headers present plus the length of the first segment
only. (Note: the IP layer can form true IPv6 jumbograms (as opposed
to parcels) by instead setting the Payload Length field to 0.)
An IP parcel therefore has the following structure:
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+--------+--------+--------+--------+
| |
~ Segment J (K octets) ~
| |
+--------+--------+--------+--------+
~ ~
~ ~
+--------+--------+--------+--------+
| |
~ Segment 3 (L octets) ~
| |
+--------+--------+--------+--------+
| |
~ Segment 2 (L octets) ~
| |
+--------+--------+--------+--------+
| |
~ Segment 1 (L octets) ~
| |
+--------+--------+--------+--------+
| IP Header Plus Extensions |
~ {Total, Payload} Length = M ~
| Jumbo Payload Length = N |
+--------+--------+--------+--------+
Figure 11: OMNI Interface IP Parcels
where J is the total number of segments (between 1 and 64), L is the
length of each non-final segment which MUST NOT be larger than 65535
(minus headers as above) and K is the length of the final segment
which MUST NOT be larger than L. The values M and N are then set to
the length of the IP header plus extensions for IPv4 or to the length
of the extensions only for IPv6, then further calculated as follows:
M = M + ((J-1) ? L : K)
N = N + (((J-1) * L) + K)
Note: a "singleton" parcel is one that includes only the IP header
plus extensions with a single segment of length K, while a "null"
parcel is a singleton with K=0, i.e., a parcel consisting of only the
IP header plus extensions with no octets beyond.
When the IP layer forwards a parcel, the OMNI interface invokes the
OAL which forwards it to either a Client as an intermediate node or
the final destination itself. The OAL source first assigns a
monotonically-incrementing (modulo 127) "Parcel ID" and subdivides
the parcel into sub-parcels no larger than the maximum of the path
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MTU to the next hop or 64KB (minus the length of encapsulation
headers). The OAL source determines the number of segments of length
L that can fit into each sub-parcel under these size constraints,
e.g. if the OAL source determines that a sub-parcel can contain 3
segments of length L, it creates sub-parcels with the first
containing segments 1-3, the second containing segments 4-6, etc. and
with the final containing any remaining segments. The OAL source
then appends an identical IP header plus extensions to each sub-
parcel while resetting M and N in each according to the above
equations with J set to 3 and K set to L for each non-final sub-
parcel and with J set to the remaining number of segments for the
final sub-parcel.
The OAL source next performs encapsulation on each sub-parcel with
destination set to the next hop address. If the next hop is reached
via an ANET/INET interface, the OAL source inserts an OAL header the
same as discussed in Section 6.1 and sets the destination to the MNP-
ULA of the target Client. If the next hop is reached via an ENET
interface, the OAL source instead inserts an IP header of the
appropriate protocol version for the underlay ENET (i.e., even if the
encapsulation header is IPv4) and sets the destination to the ENET IP
address of the next hop. The OAL source inserts the encapsulation
header even if no actual fragmentation is needed and/or even if the
Jumbo Payload option is present.
The OAL source next assigns an Identification number that is
monotonically-incremented for each consecutive sub-parcel, calculates
and appends the OAL checksum, then performs IPv6 fragmentation over
the sub-parcel if necessary to create fragments small enough to
traverse the path to the next hop. (If the encapsulation header is
IPv4, the OAL source first translates the encapsulation header into
an IPv6 header with IPv4-Compatible IPv6 addresses before performing
the fragmentation/reassembly operation while inserting an IPv6
Fragment Header.) The OAL source then writes the "Parcel ID" and
sets/clears the "(P)arcel" and "(More) (S)ub-Parcels" bits in the
Fragment Header of the first fragment (see: Figure 5). (The OAL
source sets P to 1 for a parcel or to 0 for a non-parcel. When P is
1, the OAL next sets S to 1 for non-final sub-parcels or to 0 if the
sub-parcel contains the final segment.) The OAL source then forwards
each IP encapsulated packet/fragment to the next hop (i.e., after
first translating the IPv6 encapsulation header back to IPv4 if
necessary).
When the next hop receives the encapsulated IP fragments or whole
packets, it acts as an OAL destination and reassembles if necessary
(i.e., after first translating the IPv4 encapsulation header to IPv6
if necessary). If the P flag in the first fragment is 0, the OAL
destination then processes the reassembled entity as an ordinary IP
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packet; otherwise it continues processing as a sub-parcel. If the
OAL destination is not the final destination, it retains the sub-
parcels along with their Parcel ID and Identification values for a
brief time in hopes of re-combining with peer sub-parcels of the same
original parcel identified by the 4-tuple consisting of the IP
encapsulation source and destination, Identification and Parcel ID.
The OAL destination re-combines peers by concatenating the segments
included in sub-parcels with the same Parcel ID and with
Identification values within 64 of one another to create a larger
sub-parcel possibly even as large as the entire original parcel.
Order of concatenation is not important, with the exception that the
final sub-parcel (i.e., the one with S set to 0) must occur as the
final concatenation before transmission. The OAL destination then
appends a common IP header plus extensions to each re-combined sub-
parcel while resetting M and N in each according to the above
equations with J, K and L set accordingly.
When the current OAL destination is an intermediate node, it next
becomes an OAL source to forward the re-combined (sub-)parcel(s) to
the next hop toward the final destination using encapsulation/
translation the same as specified above. (Each such intermediate
node MUST ensure that the S flag remains set to 0 in the sub-parcel
that contains the final segment.) When the parcel or sub-parcels
arrive at the final OAL destination, it re-combines them into the
largest possible (sub)-parcels while honoring the S flag then
delivers them to upper layers which act on the enclosed 5-tuple
information supplied by the original source.
Note: while the final destination may be tempted to re-combine the
sub-parcels of multiple different parcels with identical upper layer
protocol 5-tuples and with non-final segments of identical length,
this process could become complicated when the different parcels each
have final segments of diverse lengths. Since this could possibly
defeat any perceived performance advantages, the decision of whether
and how to perform inter-parcel concatenation is an implementation
matter.
7. Frame Format
When the OMNI interface forwards original IP packets from the network
layer it first invokes the OAL to create OAL packets/fragments if
necessary, then includes any L2 encapsulations and finally engages
the native frame format of the underlay interface. For example, for
Ethernet-compatible interfaces the frame format is specified in
[RFC2464], for aeronautical radio interfaces the frame format is
specified in standards such as ICAO Doc 9776 (VDL Mode 2 Technical
Manual), for various forms of tunnels the frame format is found in
the appropriate tunneling specification, etc.
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See Figure 2 for a map of the various L2 layering combinations
possible. For any layering combination, the final layer (e.g., UDP,
IP, Ethernet, etc.) must have an assigned number and frame format
representation that is compatible with the selected underlay
interface.
8. Link-Local Addresses (LLAs)
[RFC4861] requires that nodes assign Link-Local Addresses (LLAs) to
all interfaces, and that routers use their LLAs as the source address
for RA and Redirect messages. OMNI interfaces honor the first
requirement, but do not honor the second since the OMNI link could
consist of the concatenation of multiple links with diverse ULA
prefixes (see Section 9) but for which multiple nodes might configure
identical interface identifiers. OMNI interface LLAs are therefore
considered only as context for interface identifier formation as
discussed below and have no other operational role.
OMNI interfaces assign IPv6 LLAs through pre-service administrative
actions. Clients assign "MNP-LLAs" with interface identifiers that
embed the Client's unique MNP, while Proxy/Servers assign "ADM-LLAs"
that include a randomly-generated interface identifier. LLAs are
configured as follows:
* IPv6 MNP-LLAs encode the most-significant 64 bits of an MNP within
the least-significant 64 bits of the IPv6 link-local prefix
fe80::/64, i.e., in the LLA "interface identifier" portion. The
prefix length for the LLA is determined by adding 64 to the MNP
prefix length. For example, for the MNP 2001:db8:1000:2000::/56
the corresponding MNP-LLA prefix is fe80::2001:db8:1000:2000/120.
(The base MNP-LLA for each "/N" prefix sets the final 128-N bits
to 0, but all MNP-LLAs that match the prefix are also accepted.)
Non-MNP IPv6 prefix-based LLAs are also represented the same as
for MNP-LLAs, but include a GUA prefix that is not properly
covered by the MSP.
* IPv4-Compatible MNP-LLAs are constructed as fe80::{IPv4}, i.e.,
the interface identifier consists of 32 '0' bits followed by a 32
bit IPv4 address/prefix, which may be either public or private in
correspondence with the network layer addressing plan. The prefix
length for the MNP-LLA is determined by adding 96 to the IPv4
prefix length. For example, the IPv4-Compatible MNP-LLA for
192.0.2.0/24 is fe80::192.0.2.0/120, also written as
fe80::c000:0200/120. (The base MNP-LLA for each "/N" prefix sets
the final 128-N bits to 0, but all MNP-LLAs that match the prefix
are also accepted.) Non-MNP IPv4 prefix-based LLAs are also
represented the same as for MNP-LLAs, but include a GUA prefix
that is not properly covered by the MSP.
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* ADM-LLAs are randomly-generated and assigned to Proxy/Servers and
other SRT infrastructure elements. The upper 72 bits of the ADM-
LLA encode the prefix fe80::/72, and the lower 56 bits include a
randomly-generated candidate pseudo-random value configured as
specified in Section 3 of [RFC4193]; if the most significant 24
bits of the 56 bit candidate encodes the value '0', the
administrator generates a new candidate to obtain one with a
different most significant 24 bits. The ADM-LLA fe80::/128 (i.e.,
one with the lower 56 bits all set to 0) is considered the Subnet
Router Anycast ADM-LLA.
Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no
MNPs can be allocated from that block ensuring that there is no
possibility for overlap between the different MNP- and ADM-LLA
constructs discussed above.
Since MNP-LLAs are based on the distribution of administratively
assured unique MNPs, and since ADM-LLAs are guaranteed unique through
pseudo-random assignment, OMNI interfaces set the autoconfiguration
variable DupAddrDetectTransmits to 0 [RFC4862].
Note: If future protocol extensions relax the 64-bit boundary in IPv6
addressing, the additional prefix bits of an MNP could be encoded in
bits 16 through 63 of the MNP-LLA. (The most-significant 64 bits
would therefore still be in bits 64-127, and the remaining bits would
appear in bits 16 through 48.) However, this would interfere with
the relationship between OMNI LLAs and ULAs (see: Section 9) and
render many OMNI functions inoperable. The analysis provided in
[RFC7421] furthermore suggests that the 64-bit boundary will remain
in the IPv6 architecture for the foreseeable future.
9. Unique-Local Addresses (ULAs)
OMNI links use IPv6 Unique-Local Addresses (ULAs) as the source and
destination addresses in both IPv6 ND messages and OAL packet IPv6
encapsulation headers. ULAs are routable only within the scope of an
OMNI link, and are derived from the IPv6 Unique Local Address prefix
fc00::/7 followed by the L bit set to 1, i.e., as fd00::/8. When the
first 16 bits of the ULA encode the value fd00::/16, the address is
considered as either an MNP eXtended ULA (MNP-XLA) or a Temporary ULA
(TMP-ULA) - see below. For all other ULAs, the remaining 120 bits
following fd00::/8 encode a 40-bit Global ID followed by a 16-bit
Subnet ID then finally a 64 bit Interface ID as specified in
Section 3 of [RFC4193] to form an ADM-ULA.
For ADM-ULAs, an administrator selects a 40-bit Global ID for the
OMNI link by generating a candidate pseudo-random value as specified
in Section 3 of [RFC4193]; if the most significant 8 bits of the
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candidate encodes the value '0', the administrator generates a new
candidate until it obtains one with a different most significant 8
bits. All nodes on the same OMNI link use the same Global ID, and
statistical uniqueness of the pseudo-random Global ID provides a
unique OMNI link identifier allowing different links to be joined
together in the future without requiring renumbering.
Next, for each logical segment of the same OMNI link the
administrator selects a 16-bit Subnet ID value between 0x0000 and
0xffff. Nodes on the same logical segment configure the same Subnet
ID, but nodes on different segments of the same OMNI link can still
coordinate as single-hop neighbors even if they configure different
Subnet IDs. When a node moves to a different OMNI link segment, it
resets the Global ID and Subnet ID value according to the new segment
but need not change the interface ID.
ULAs and their associated prefix lengths are configured in
correspondence with LLAs through stateless prefix translation where
"MNP-ULAs" are assigned in correspondence to MNP-LLAs and "ADM-ULAs"
are assigned in correspondence to ADM-LLAs. For example, for the
OMNI link ULA prefix fd{Global}:{Subnet}::/64:
* the MNP-ULA corresponding to the MNP-LLA fe80::2001:db8:1:2 with a
56-bit MNP length is derived by copying the lower 64 bits of the
LLA into the ULA lower 64 bits as
fd{Global}:{Subnet}:2001:db8:1:2/120 (where, the ULA prefix length
becomes 64 plus the IPv6 MNP length).
* the MNP-ULA corresponding to fe80::192.0.2.0 with a 28-bit MNP
length is derived by simply writing the LLA interface ID into the
ULA lower 64 bits as fd{Global}:{Subnet}::192.0.2.0/124 (where,
the ULA prefix length is 64 plus 32 plus the IPv4 MNP length).
* the ADM-ULA corresponding to fe80::1234:5678:9abc is simply
fd{Global}:{Subnet}::1234:5678:9abc.
* the ADM-ULA corresponding to fe80::/128 is simply
fd{Global}:{Subnet}::/128.
The ULA presents an IPv6 address format that is routable within the
OMNI link routing system and can be used to convey link-scoped (i.e.,
single-hop) IPv6 ND messages across multiple hops using IPv6
encapsulation [RFC2473]. The OMNI link extends across one or more
underlying Internetworks to include all Proxy/Servers and other
service nodes. All Clients are also considered to be connected to
the OMNI link, however unnecessary encapsulations are omitted
whenever possible to conserve bandwidth (see: Section 14).
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Clients also use MNP-XLAs as the "default" ULA for carrying their
MNP. MNP-XLAs use the ULA prefix fd00::/64 and include a 64-bit MNP
in the interface identifier the same as for MNP-{LLA,ULA}s. (Note
that MNP-XLAs can be formed from MNP-LLAs simply by inverting bits 7
and 8 of 'fe80' to form 'fd00'.) Clients use MNP-XLAs when they
already know their MNP but need to express it outside the context of
a specific ULA prefix, and Proxy/Servers advertise MNP-XLAs into the
routing system instead of advertising fully-qualified MNP-ULAs and/or
non-routable MNP-LLAs.
Clients can also configure TMP-ULAs when they have no other ULA
addresses by setting the ULA prefix to fd00::/16 followed by an
entirely randomly-generated 112 bit number per the algorithm in
[RFC8981]. Clients form TMP-ULAs when they do not already have a
delegated MNP by first generating a candidate 48 bit random value
other than all-zeros, then generating an additional 64-bit random
value to form the 112 bit pseudo-random value.
MNP-XLAs and TMP-ULAs provide an initial "bootstrapping" address
while the Client is in the process of procuring an MNP and/or
identifying the ULA prefix for the OMNI link segment; TMP-ULAs are
not routable within the OMNI link routing system but can be used for
Client-to-Client communications within a single *NET when no OMNI
link infrastructure is present. Within each individual *NET, random
TMP-ULAs employ optimistic DAD principles [RFC4429] since they are
statistically unique.
Each OMNI link may be subdivided into SRT segments that often
correspond to different administrative domains or physical
partitions. Each SRT segment is identified by a different Subnet ID
within the same ULA ::/48 prefix. Multiple distinct OMNI links with
different ULA ::/48 prefixes can also be joined together into a
single unified OMNI link through simple interconnection without
requiring renumbering. In that case, the (larger) unified OMNI link
routing system may carry multiple distinct ULA prefixes.
OMNI nodes can use Segment Routing [RFC8402] to support efficient
forwarding to destinations located in other OMNI link segments. A
full discussion of Segment Routing over the OMNI link appears in
[I-D.templin-6man-aero].
Note: IPv6 ULAs taken from the prefix fc00::/7 followed by the L bit
set to 0 (i.e., as fc00::/8) are never used for OMNI OAL addressing,
however the range could be used for MSP/MNP addressing under certain
limiting conditions (see: Section 10).
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Note: When they appear in routing tables, ADM-ULAs always use prefix
lengths between /48 and /64 while MNP-ULAs and MNP-XLAs always use
prefix lengths between /65 and /128. ADM-ULAs can also appear in
routing tables as prefixes of length /128.
10. Global Unicast Addresses (GUAs)
OMNI domains use IP Global Unicast Address (GUA) prefixes [RFC4291]
as Mobility Service Prefixes (MSPs) from which Mobile Network
Prefixes (MNP) are delegated to Clients. Fixed correspondent node
networks reachable from the OMNI link are represented by non-MNP GUA
prefixes that are not derived from the MSP, but are treated in all
other ways the same as for MNPs.
For IPv6, GUA MSPs are assigned by IANA [IPV6-GUA] and/or an
associated Regional Internet Registry (RIR) such that the OMNI link
can be interconnected to the global IPv6 Internet without causing
inconsistencies in the routing system. An OMNI link could instead
use ULAs with the 'L' bit set to 0 (i.e., from the prefix
fc00::/8)[RFC4193], however this would require IPv6 NAT if the domain
were ever connected to the global IPv6 Internet.
For IPv4, GUA MSPs are assigned by IANA [IPV4-GUA] and/or an
associated RIR such that the OMNI link can be interconnected to the
global IPv4 Internet without causing routing inconsistencies. An
OMNI ANET/ENET could instead use private IPv4 prefixes (e.g.,
10.0.0.0/8, etc.) [RFC3330], however this would require IPv4 NAT at
the INET-to-ANET/ENET boundary. OMNI interfaces advertise IPv4 MSPs
into IPv6 routing systems as IPv4-Compatible IPv6 prefixes [RFC4291]
(e.g., the IPv6 prefix for the IPv4 MSP 192.0.2.0/24 is
::192.0.2.0/120).
OMNI interfaces assign the IPv4 anycast address TBD3 (see: IANA
Considerations), and IPv4 routers that configure OMNI interfaces
advertise the prefix TBD3/N into the routing system of other networks
(see: IANA Considerations). OMNI interfaces also configure global
IPv6 anycast addresses formed according to [RFC3056] as:
2002:TBD3{32}:MSP{64}:Link-ID{16}
where TBD3{32} is the 32 bit IPv4 anycast address and MSP{64} encodes
an MSP zero-padded to 64 bits (if necessary). For example, the OMNI
IPv6 anycast address for MSP 2001:db8::/32 is
2002:TBD3{32}:2001:db8:0:0:{Link-ID}, the OMNI IPv6 anycast address
for MSP 192.0.2.0/24 is 2002:TBD3{32}::c000:0200:{Link-ID}, etc.).
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The16-bit Link-ID in the OMNI IPv6 anycast address identifies a
specific OMNI link within the domain that services the MSP. The
special Link-ID value '0' is a wildcard that matches all links, while
all other values identify specific links. Mappings between Link-ID
values and the ULA Global IDs assigned to OMNI links are outside the
scope of this document.
OMNI interfaces assign OMNI IPv6 anycast addresses, and IPv6 routers
that configure OMNI interfaces advertise the corresponding prefixes
into the routing systems of other networks. An OMNI IPv6 anycast
prefix is formed the same as for any IPv6 prefix; for example, the
prefix 2002:TBD3{32}:2001:db8::/80 matches all OMNI IPv6 anycast
addresses covered by the prefix. When IPv6 routers advertise OMNI
IPv6 anycast prefixes in this way, Clients can locate and associate
with either a specific OMNI link or any OMNI link within the domain
that services the MSP of interest.
OMNI interfaces use OMNI IPv6 and IPv4 anycast addresses to support
Service Discovery in the spirit of [RFC7094], i.e., the addresses are
not intended for use in long-term transport protocol sessions.
Specific applications for OMNI IPv6 and IPv4 anycast addresses are
discussed throughout the document as well as in
[I-D.templin-6man-aero].
11. Node Identification
OMNI Clients and Proxy/Servers that connect over open Internetworks
include a unique node identification value for themselves in the OMNI
options of their IPv6 ND messages (see: Section 12.2.12). An example
identification value alternative is the Host Identity Tag (HIT) as
specified in [RFC7401], while Hierarchical HITs (HHITs)
[I-D.ietf-drip-rid] may be more appropriate for certain domains such
as the Unmanned (Air) Traffic Management (UTM) service for Unmanned
Air Systems (UAS). Another example is the Universally Unique
IDentifier (UUID) [RFC4122] which can be self-generated by a node
without supporting infrastructure with very low probability of
collision.
When a Client is truly outside the context of any infrastructure, it
may have no MNP information at all. In that case, the Client can use
a TMP-ULA or (H)HIT as an IPv6 source/destination address for
sustained communications in Vehicle-to-Vehicle (V2V) and (multihop)
Vehicle-to-Infrastructure (V2I) scenarios. The Client can also
propagate the ULA/(H)HIT into the multihop routing tables of
(collective) Mobile/Vehicular Ad-hoc Networks (MANETs/VANETs) using
only the vehicles themselves as communications relays.
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When a Client connects via a protected-spectrum ANET, an alternate
form of node identification (e.g., MAC address, serial number,
airframe identification value, VIN, etc.) embedded in an LLA/ULA may
be sufficient. The Client can then include OMNI "Node
Identification" sub-options (see: Section 12.2.12) in IPv6 ND
messages should the need to transmit identification information over
the network arise.
12. Address Mapping - Unicast
OMNI interfaces maintain a neighbor cache for tracking per-neighbor
state and use the link-local address format specified in Section 8.
IPv6 Neighbor Discovery (ND) [RFC4861] messages sent over OMNI
interfaces without encapsulation observe the native underlay
interface Source/Target Link-Layer Address Option (S/TLLAO) format
(e.g., for Ethernet the S/TLLAO is specified in [RFC2464]). IPv6 ND
messages sent over OMNI interfaces using encapsulation do not include
S/TLLAOs, but instead include a new option type that encodes
encapsulation addresses, interface attributes and other OMNI link
information. Hence, this document does not define an S/TLLAO format
but instead defines a new option type termed the "OMNI option"
designed for these purposes. (Note that OMNI interface IPv6 ND
messages sent without encapsulation may include both OMNI options and
S/TLLAOs, but the information conveyed in each is mutually
exclusive.)
OMNI interfaces prepare IPv6 ND messages that include one or more
OMNI options (and any other IPv6 ND options) then completely populate
all option information. If the OMNI interface includes an
authentication signature, it sets the IPv6 ND message Checksum field
to 0 and calculates the authentication signature over the length of
the entire OAL packet or super-packet (beginning with a pseudo-header
of the IPv6 ND message IPv6 header) but does not calculate/include
the IPv6 ND message checksum itself. Otherwise, the OMNI interface
calculates the standard IPv6 ND message checksum over the entire OAL
packet or super-packet and writes the value in the Checksum field.
OMNI interfaces verify authentication and/or integrity of each IPv6
ND message received according to the specific check(s) included, and
process the message further only following verification.
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OMNI interface Clients such as aircraft typically have multiple
wireless data link types (e.g. satellite-based, cellular,
terrestrial, air-to-air directional, etc.) with diverse performance,
cost and availability properties. The OMNI interface would therefore
appear to have multiple L2 connections, and may include information
for multiple underlay interfaces in a single IPv6 ND message
exchange. OMNI interfaces manage their dynamically-changing
multilink profiles by including OMNI options in IPv6 ND messages as
discussed in the following subsections.
12.1. The OMNI Option
OMNI options appear in IPv6 ND messages formatted as shown in
Figure 12:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-Options ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: OMNI Option Format
In this format:
* Type is set to TBD4 (see: IANA Considerations).
* Length is set to the number of 8 octet blocks in the option. The
value 0 is invalid, while the values 1 through 255 (i.e., 8
through 2040 octets, respectively) indicate the total length of
the OMNI option. If multiple OMNI option instances appear in the
same IPv6 ND message, the union of the contents of all OMNI
options is accepted unless otherwise qualified for specific sub-
options below.
* Sub-Options is a Variable-length field padded if necessary such
that the complete OMNI Option is an integer multiple of 8 octets
long. Sub-Options contains zero or more sub-options as specified
in Section 12.2.
The OMNI option is included in all OMNI interface IPv6 ND messages;
the option is processed by receiving interfaces that recognize it and
otherwise ignored. The OMNI interface processes all OMNI option
instances received in the same IPv6 ND message in the consecutive
order in which they appear. The OMNI option(s) included in each IPv6
ND message may include full or partial information for the neighbor.
The OMNI interface therefore retains the union of the information in
the most recently received OMNI options in the corresponding NCE.
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12.2. OMNI Sub-Options
Each OMNI option includes a Sub-Options block containing zero or more
individual sub-options. Each consecutive sub-option is concatenated
immediately following its predecessor. All sub-options except Pad1
(see below) are in an OMNI-specific type-length-value (TLV) format
encoded as follows:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Sub-Type| Sub-Length | Sub-Option Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 13: Sub-Option Format
* Sub-Type is a 5-bit field that encodes the sub-option type. Sub-
option types defined in this document are:
Sub-Option Name Sub-Type
Pad1 0
PadN 1
Neighbor Coordination 2
Interface Attributes 3
Multilink Forwarding Params 4
Traffic Selector 5
Geo Coordinates 6
DHCPv6 Message 7
HIP Message 8
PIM-SM Message 9
Fragmentation Report 10
Node Identification 11
ICMPv6 Error 12
QUIC-TLS Message 13
Proxy/Server Departure 14
Sub-Type Extension 30
Figure 14
Sub-Types 15-29 are available for future assignment for major
protocol functions, while Sub-Type 30 supports scalable extension
to include other functions. Sub-Type 31 is reserved by IANA.
* Sub-Length is an 11-bit field that encodes the length of the Sub-
Option Data in octets.
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* Sub-Option Data is a block of data with format determined by Sub-
Type and length determined by Sub-Length. Note that each
individual sub-option may end on an arbitrary octet boundary,
whereas the OMNI option itself must include padding if necessary
for 8-octet alignment.
The OMNI interface codes each sub-option with a 2 octet header that
includes Sub-Type in the most significant 5 bits followed by Sub-
Length in the next most significant 11 bits. Each sub-option encodes
a maximum Sub-Length value of 2038 octets minus the lengths of the
OMNI option header and any preceding sub-options. This allows ample
Sub-Option Data space for coding large objects (e.g., ASCII strings,
domain names, protocol messages, security codes, etc.), while a
single OMNI option is limited to 2040 octets the same as for any IPv6
ND option.
The OMNI interface codes initial sub-options in a first OMNI option
instance and subsequent sub-options in additional instances in the
same IPv6 ND message in the intended order of processing. The OMNI
interface can then code any remaining sub-options in additional IPv6
ND messages if necessary. Implementations must observe these size
limits and refrain from sending IPv6 ND messages larger than the OMNI
interface MTU.
The OMNI interface processes all OMNI option Sub-Options received in
an IPv6 ND message while skipping over and ignoring any unrecognized
sub-options. The OMNI interface processes the Sub-Options of all
OMNI option instances in the consecutive order in which they appear
in the IPv6 ND message, beginning with the first instance and
continuing through any additional instances to the end of the
message. If an individual sub-option length would cause processing
to exceed the OMNI option instance and/or IPv6 ND message lengths,
the OMNI interface accepts any sub-options already processed and
ignores the remainder of that instance. The interface then processes
any remaining OMNI option instances in the same fashion to the end of
the IPv6 ND message.
When an OMNI interface includes an authentication sub-option (e.g.,
see: Section 12.2.9), it MUST appear as the first sub-option of the
first OMNI option which must appear immediately following the IPv6 ND
message header (all other authentication sub-options are ignored).
If the IPv6 ND message is the first packet in a combined OAL super-
packet, the OMNI interface calculates the authentication signature
over the entire length of the super-packet, i.e., and not just to the
end of the IPv6 ND message itself. When the first sub-option is not
authentication, the OMNI interface instead calculates the IPv6 ND
message checksum over the entire length of the packet/super-packet.
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When a Client OMNI interface prepares a secured unicast RS message,
it includes an Interface Attributes sub-option specific to the
underlay interface that will transmit the RS (see: Section 12.2.4)
immediately following the authentication and header extension sub-
options if present; otherwise as the first sub-option of the first
OMNI option which must appear immediately following the IPv6 ND
message header. When a Client OMNI interface prepares a secured
unicast NS message, it instead includes a Multilink Forwarding
Parameters sub-option specific to the underlay interface that will
transmit the NS (see: Section 12.2.5).
Note: large objects that exceed the maximum Sub-Option Data length
are not supported under the current specification; if this proves to
be limiting in practice, future specifications may define support for
fragmenting large sub-options across multiple OMNI options within the
same IPv6 ND message (or even across multiple IPv6 ND messages, if
necessary).
The following sub-option types and formats are defined in this
document:
12.2.1. Pad1
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| S-Type=0|x|x|x|
+-+-+-+-+-+-+-+-+
Figure 15: Pad1
* Sub-Type is set to 0. If multiple instances appear in OMNI
options of the same message all are processed.
* Sub-Type is followed by 3 'x' bits, set to any value on
transmission (typically all-zeros) and ignored on reception. Pad1
therefore consists of 1 octet with the most significant 5 bits set
to 0, and with no Sub-Length or Sub-Option Data fields following.
If more than one octet of padding is required, the PadN option,
described next, should be used, rather than multiple Pad1 options.
12.2.2. PadN
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0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| S-Type=1| Sub-length=N | N padding octets ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 16: PadN
* Sub-Type is set to 1. If multiple instances appear in OMNI
options of the same message all are processed.
* Sub-Length is set to N that encodes the number of padding octets
that follow.
* Sub-Option Data consists of N octets, set to any value on
transmission (typically all-zeros) and ignored on receipt.
When a proxy forwards an IPv6 ND message with OMNI options, it can
employ PadN to cancel any sub-options (other than Pad1) that should
not be processed by the next hop by simply writing the value '1' over
the Sub-Type. When the proxy alters the IPv6 ND message contents in
this way, any included authentication and integrity checks are
invalidated. See: Appendix B for a discussion of IPv6 ND message
authentication and integrity.
12.2.3. Neighbor Coordination
IPv6 ND messages used for Prefix Length assertion, service
coordination and/or Window Synchronization include a Neighbor
Coordination sub-option. If a Neighbor Coordination sub-option is
included, it must appear immediately after the authentication sub-
option if present; otherwise, as the first (non-padding) sub-option
of the first OMNI option. If multiple Neighbor Coordination sub-
options are included (whether in a single OMNI option or multiple),
only the first is processed and all others are ignored.
The Neighbor Coordination sub-option is formatted as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=2| Sub-length=14 | Preflen |N|A|U| Reservd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Acknowledgment Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|A|R|O|P| | |
|Y|C|S|P|N| Res | Window |
|N|K|T|T|G| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: Neighbor Coordination
* Sub-Type is set to 2.
* Sub-Length is set to 14.
* The first two octets of Sub-Option Data contains a 1-octet Prefix
Length followed by a 1-octet flags field interpreted as follows:
- Preflen is an 8 bit field that determines the length of prefix
associated with a ULA. Values 0 through 128 specify a valid
prefix length (if any other value appears the OMNI option must
be ignored). For IPv6 ND messages sent from a Client to the
MS, Preflen applies to the IPv6 source ULA and provides the
length that the Client is requesting from or asserting to the
MS. For IPv6 ND messages sent from the MS to the Client,
Preflen applies to the IPv6 destination ULA and indicates the
length that the MS is granting to the Client. For IPv6 ND
messages sent between MS endpoints, Preflen provides the length
associated with the source/target Client MNP that is subject of
the ND message. When an IPv6 ND RS/RA message sets Preflen to
0, the recipient regards the message as a prefix release
indication.
- The N/A/U flags are set or cleared in Client RS messages as
directives to FHS and Hub Proxy/Servers and ignored in all
other IPv6 ND messages. When an FHS Proxy/Server forwards or
processes an RS with the N flag set, it responds directly to NS
Neighbor Unreachability Detection (NUD) messages by returning
NA(NUD) replies; otherwise, it forwards NS(NUD) messages to the
Client. When the Hub Proxy/Server receives an RS with the A
flag set, it responds directly to NS Address Resolution (AR)
messages by returning NA(AR) replies; otherwise, it forwards
NS(AR) messages to the Client. When the Hub Proxy/Server
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receives an RS with the U flag set, it maintains a Report List
of recent NS(AR) message sources for this Client and sends uNA
messages to all list members if any aspects of the Client's
underlay interfaces change. Proxy/Servers function according
to the N/A/U flag settings received in the most recent RS
message to support dynamic Client updates. In all IPv6 ND
messages, the remaining 5 flag bits are set to 0 on
transmission and ignored on reception.
* The remainder of Sub-Option Data contains a 4-octet Sequence
Number, followed by a 4-octet Acknowledgement Number, followed by
a 1-octet flags field followed by a 3-octet Window size modeled
from the Transmission Control Protocol (TCP) header specified in
Section 3.1 of [RFC0793]. The (SYN, ACK, RST) flags are used for
TCP-like window synchronization, while the TCP (URG, PSH, FIN)
flags are not used and therefore omitted. The (OPT, PNG) flags
are OMNI-specific, and the remaining flags are Reserved.
Together, these fields support the asymmetric and symmetric OAL
window synchronization services specified in Section 6.6.
12.2.4. Interface Attributes
The Interface Attributes sub-option provides neighbors with
forwarding information for the multilink conceptual sending algorithm
discussed in Section 14. Neighbors use the forwarding information to
selecting among potentially multiple candidate underlay interfaces
that can be used to forward carrier packets to the neighbor based on
factors such as traffic selectors and link quality. Interface
Attributes further include link-layer address information to be used
for either direct INET encapsulation for targets in the local SRT
segment or spanning tree forwarding for targets in remote SRT
segments.
OMNI nodes include Interface Attributes for some/all of a target
Client's underlay interfaces in NS/NA and uNA messages used to
publish Client information (see: [I-D.templin-6man-aero]). At most
one Interface Attributes sub-option for each distinct omIndex may be
included; if an NS/NA message includes multiple Interface Attributes
sub-options for the same omIndex, the first is processed and all
others are ignored. OMNI nodes that receive NS/NA messages can use
all of the included Interface Attributes and/or Traffic Selectors to
formulate a map of the prospective target node as well as to seed the
information to be populated in a Multilink Forwarding Parameters sub-
option (see: Section 12.2.5).
OMNI Clients and Proxy/Servers also include Interface Attributes sub-
options in RS/RA messages used to initialize, discover and populate
routing and addressing information. Each RS message MUST contain
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exactly one Interface Attributes sub-option with an omIndex
corresponding to the Client's underlay interface used to transmit the
message, and each RA message MUST echo the same Interface Attributes
sub-option with any (proxyed) information populated by the FHS Proxy/
Server to provide operational context.
OMNI Client RS and Proxy/Server RA messages MUST include the
Interface Attributes sub-option for the Client underlay interface in
the first OMNI option immediately following the Neighbor Coordination
and/or authentication sub-option(s) if present; otherwise,
immediately following the OMNI header. When an FHS Proxy/Server
receives an RS message destined to an anycast L2 address, it MUST
include an Interface Attributes sub-option with omIndex '0' that
encodes its unicast L2 address relative to the Client's underlay
interface immediately after the Interface Attributes sub-option in
the solicited RA response. Any additional Interface Attributes sub-
options that appear in RS/RA messages are ignored.
The Interface Attributes sub-options are formatted as shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=3| Sub-length=N | omIndex | omType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Provider ID | Link | Resvd | FMT | SRT | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ LHS Proxy/Server ULA/INADDR ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: Interface Attributes
* Sub-Type is set to 3.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
* Sub-Option Data contains an "Interface Attributes" option encoded
as follows:
- omIndex is a 1-octet value corresponding to a specific underlay
interface. Client OMNI interfaces MUST number each distinct
underlay interface with an omIndex value between '1' and '255'
that represents a Client-specific 8-bit mapping for the actual
ifIndex value assigned by network management [RFC2863], then
set omIndex to either a specific omIndex value or '0' to denote
"unspecified".
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- omType is set to an 8-bit integer value corresponding to the
underlay interface identified by omIndex. The value represents
an OMNI interface-specific 8-bit mapping for the actual IANA
ifType value registered in the 'IANAifType-MIB' registry
[http://www.iana.org].
- Provider ID is set to an OMNI interface-specific 8-bit ID value
for the network service provider associated with this omIndex.
- Link encodes a 4-bit link metric. The value '0' means the link
is DOWN, and the remaining values mean the link is UP with
metric ranging from '1' ("lowest") to '15' ("highest").
- Resvd is a 4-bit Reserved field set to 0 on transmission and
ignored on reception.
- FMT - a 3-bit "Forward/Mode/Type" code interpreted as follows:
o The most significant two bits (i.e., "FMT-Forward" and "FMT-
Mode") are interpreted in conjunction with one another.
When FMT-Forward is clear, the LHS Proxy/Server performs OAL
reassembly and decapsulation to obtain the original IP
packet before forwarding. If the FMT-Mode bit is clear, the
LHS Proxy/Server then forwards the original IP packet at
layer 3; otherwise, it invokes the OAL to re-encapsulate,
re-fragment and forwards the resulting carrier packets to
the Client via the selected underlay interface. When FMT-
Forward is set, the LHS Proxy/Server forwards unsecured OAL
fragments to the Client without reassembling, while
reassembling secured OAL fragments before re-fragmenting and
forwarding to the Client. If FMT-Mode is clear, all carrier
packets destined to the Client must always be forwarded
through the LHS Proxy/Server; otherwise the Client is
eligible for direct forwarding over the open INET where it
may be located behind one or more NATs.
o The least significant bit (i.e., "FMT-Type") determines the
length of the LHS Proxy/Server INADDR field. If FMT-Type is
clear, INADDR includes a 4-octet IPv4 address; otherwise, a
16-octet IPv6 address. (Note: the INADDR "short form"
minimizes overhead for ND messages that include many
Interface Attributes sub-options with IPv4 addresses.)
- SRT - a 5-bit Segment Routing Topology prefix length value
between 0 and 16 that (when added to 48) determines the prefix
length associated with the LHS ULA Subnet ID. For example, the
value 5 corresponds to the prefix ULA::/53.
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- LHS Proxy/Server ULA/INADDR - the first 15 octets following the
"FMT/SRT" octet includes the 120 least significant bits of the
ULA of the LHS Proxy/Server on the path from a source neighbor
to the target Client's underlay interface. (Note that the FMT/
SRT code is replaced with the value "fd" after processing to
form a proper Proxy/Server ULA.) When SRT and ULA are both set
to 0, the LHS Proxy/Server is considered unspecified in this
IPv6 ND message. FMT, SRT and LHS together provide guidance
for the OMNI interface forwarding algorithm. Specifically, if
SRT/LHS is located in the local OMNI link segment, then the
source can reach the target Client either through its dependent
Proxy/Server or through direct encapsulation following NAT
traversal according to FMT. Otherwise, the target Client is
located on a different SRT segment and the path from the source
must employ a combination of route optimization and spanning
tree hop traversals. INADDR identifies the LHS Proxy/Server's
INET-facing interface not located behind NATs, therefore no UDP
port number is included since port number 8060 is used when the
L2 encapsulation includes a UDP header. Instead, INADDR
includes only a 4-octet IPv4 or 16-octet IPv6 address with type
and length determined by FMT-Type. The IP address is recorded
in network byte order in ones-compliment "obfuscated" form per
[RFC4380].
12.2.5. Multilink Forwarding Parameters
OMNI nodes include the Multilink Forwarding Parameters sub-option in
NS/NA messages used to coordinate with multilink route optimization
targets. If an NS message includes the sub-option, the solicited NA
response must also include the sub-option. The OMNI node MUST
include the sub-option in the first OMNI option immediately following
the Neighbor Coordination and/or authentication message sub-option(s)
if present. Otherwise, the OMNI node MUST include the sub-option
immediately following the OMNI header. Each NS/NA message may
contain at most one Multilink Forwarding Parameters sub-option; if an
NS/NA message contains additional Multilink Forwarding Parameters
sub-options, the first is processed and all others are ignored.
When an NS/NA message includes the sub-option, the FHS Client omIndex
MUST correspond to the underlay interface used to transmit the
message. When the NS/NA message also includes Interface Attributes
sub-options any that include the same FHS/LHS Client omIndex are
ignored while all others are processed.
The Multilink Forwarding Parameters sub-option includes the necessary
state for establishing Multilink Forwarding Vectors (MFVs) in the
Multilink Forwarding Information Bases (MFIBs) of the OAL source,
destination and intermediate nodes in the path. The sub-option also
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records addressing information for FHS/LHS nodes on the path,
including "INADDRs" which MUST be unicast IP encapsulation addresses
(i.e., and not anycast/multicast). The manner for populating
multilink forwarding information is specified in detail in
[I-D.templin-6man-aero].
The Multilink Forwarding Parameters sub-option is formatted as shown
in Figure 19:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=4| Sub-length=N | Reserved | A | B |Job|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Multilink Forwarding Vector Index (MFVI) List ~
~ (5 consecutive 4-octet MFVIs) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Tunnel Window Synchronization Parameters ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|FHS Cli omIndex| omType | Provider ID | Link | Resvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FMT | SRT | ~
+-+-+-+-+-+-+-+-+ ~
~ FHS Proxy/Server ULA/INADDR ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ FHS Gateway ULA/INADDR ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|LHS Cli omIndex| omType | Provider ID | Link | Resvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FMT | SRT | ~
+-+-+-+-+-+-+-+-+ ~
~ LHS Proxy/Server ULA/INADDR ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ LHS Gateway ULA/INADDR ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: Multilink Forwarding Parameters
* Sub-Type is set to 4. If multiple instances appear in the same
message (i.e., whether in a single OMNI option or multiple) the
first instance is processed and all others are ignored.
* Sub-Length encodes the number of Sub-Option Data octets that
follow. The length includes all fields up to and including the
Tunnel Window Synchronization Parameters for all Job codes, while
including the remaining fields only for Job codes "0" and "1" (see
below).
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* Sub-Option Data contains Multilink Forwarding Parameters as
follows:
- Reserved is a 1-octet reserved field set to 0 on transmission
and ignored on receipt.
- A/B and Job are fields that determine per-hop processing of the
MFVI List, where A is a 3-bit count of the number of "A" MVFI
List entries and B is a 3-bit count of the number of "B" MVFI
List entries (valid A/B values are 0-5). Job is a 2-bit code
interpreted as follows:
o '00' - "Initialize; Build B" - the FHS source sets this code
in an NS used to initialize MFV state (any other messages
that include this code MUST be dropped). The FHS source
first sets A/B to 0, and the FHS source and each
intermediate node along the path to the LHS destination that
processes the message creates a new MFV. Each node that
processes the message then assigns a unique 4-octet "B" MFVI
to the MVF and also writes the value into list entry B, then
increments B. When the message arrives at the LHS
destination, B will contain the number of MFVI List "B"
entries, with the FHS source entry first, followed by
entries for each consecutive intermediate node and ending
with an entry for the final intermediate node (i.e., the
list is populated in the forward direction).
o '01' - "Follow B; Build A" - the LHS source sets this code
in a solicited NA response to a solicitation with Job code
"0" (any other messages that include this code MUST be
dropped). The LHS source first copies the MFVI List and B
value from the code "0" solicitation into these fields and
sets A to 0. The LHS source and each intermediate node
along the path to the FHS destination that processes the
message then uses MFVI List entry B to locate the
corresponding MFV. Each node that processes the message
then assigns a unique 4-octet "A" MFVI to the MVF and also
writes the value into list entry B, then increments A and
decrements B. When the message arrives at the FHS
destination, A will contain the number of MFVI List "A"
entries, with the LHS source entry last, preceded by entries
for each consecutive intermediate node and beginning with an
entry for the final intermediate node (i.e., the list is
populated in the reverse direction).
o '10' - "Follow A; Record B" - the FHS node that sent the
original code "0" solicitation and received the
corresponding code "1" advertisement sets this code in any
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subsequent NS/NA messages sent to the same LHS destination.
The FHS source copies the MVFI List and A value from the
code "1" advertisement into these fields and sets B to 0.
The FHS source and each intermediate node along the path to
the LHS destination that processes the message then uses the
"A" MFVI found at list entry B to locate the corresponding
MFV. Each node that processes the message then writes the
MVF's "B" MFVI into list entry B, then decrements A and
increments B. When the message arrives at the LHS
destination, B will contain the number of MFVI List "B"
entries populated in the forward direction.
o '11' - "Follow B; Record A" - the LHS node that received the
original code "0" solicitation and sent the corresponding
code "1" advertisement sets this code in any subsequent NS/
NA messages sent to the same FHS destination. The LHS
source copies the MVFI List and B values from the code "0"
solicitation into these fields and sets A to 0. The LHS
source and each intermediate node along the path to the FHS
destination that processes the message then uses the "B"
MFVI List entry found at list entry B to locate the
corresponding MFV. Each node that processes the message
then writes the MFV's "A" MFVI into list entry B, then
increments A and decrements B. When the message arrives at
the FHS destination, A will contain the number of MFVI List
"A" entries populated in the reverse direction.
Job and A/B together determine the per-hop behavior at each
FHS/LHS source, intermediate node and destination that
processes an IPv6 ND message. When a Job code specifies
"Initialize", each FHS/LHS node that processes the message
creates a new MVF. When a Job code specifies "Build", each
node that processes the message assigns a new MFVI. When a Job
code specifies "Follow", each node that processes the message
uses an A/B MFVI List entry to locate an MFV (if the MFV cannot
be located, the node returns a parameter problem and drops the
message). Using this algorithm, FHS sources that send code
'00' solicitations and receive code '01' advertisements
discover only "A" information, while LHS sources that receive
code '00' solicitations and return code '01' advertisements
discover only "B" information. FHS/LHS intermediate nodes can
instead examine A, B and the MFVI List to determine the number
of previous hops, the number of remaining hops, and the A/B
MFVIs associated with the previous/remaining hops. However, no
intermediate nodes will discover inappropriate A/B MFVIs for
their location in the multihop forwarding chain. See:
[I-D.templin-6man-aero] for further discussion on A/B MFVI
processing.
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- Multilink Forwarding Vector Index (MFVI) List is a 20-octet
block that contains 5 consecutive 4-octet MFVI entries. The
FHS/LHS source and each intermediate node on the path to the
destination processes the list according to the Job and A/B
codes (see above). Note that the reason the MFVI list contains
at most 5 entries is that only the FHS (Client, Proxy/Server,
Gateway) and LHS (Client, Proxy/Server, Gateway) nodes are
eligible for OMNI link route optimization resulting in at most
5 MFVIs "hops" that must be exposed. All other OMNI link nodes
(i.e., downstream Clients that connect via an FHS/LHS Client)
must forward through their upstream-dependent OMNI link
neighbors without applying OMNI link route optimization.
- Tunnel Window Synchronization Parameters is a 12-octet block
that consists of a 4-octet Sequence Number followed by a
4-octet Acknowledgement Number followed by a 1-octet Flags
field followed by a 3-octet Window field (i.e., the same as for
the OMNI header parameters). Tunnel endpoints use these
parameters for simultaneous middlebox window synchronization in
a single solicitation/advertisement message exchange.
- For Job codes '00' and '01' only, two trailing state variable
blocks are included for First-Hop Segment (FHS) followed by
Last-Hop Segment (LHS) network elements. When present, each
block encodes the following information:
o Client omIndex, omType, Provider ID and Resvd/Link are
1-octet fields (at offset 0 from the beginning of the Sub-
Option Data) that include link parameters for the Client
underlay interface. These fields are populated based on
information discovered in Interface Attributes sub-options
included in earlier RS/RA and/or NS/NA exchanges.
o FMT/SRT is a 1-octet field with a 5-bit SRT prefix length
that applies to all elements in the segment. The FMT-
Forward/Mode bits determine the characteristics of the
Proxy/Server relationship for this specific Client underlay
interface (i.e., the same as described in Section 12.2.4),
and the FMT-Type bits determine the IP address version for
all INADDR fields relative to this SRT segment. Unlike the
case for Interface Attributes, all INADDR fields are always
16 bits in length regardless of the IP protocol version with
IPv4 INADDRs encoded as IPv4-Compatible IPv6 addresses
[RFC4291]. (Note: the INADDR "long-form" is used
exclusively since there may be no a priori knowledge of the
IP address version used at each hop.) The IP address is
recoded in network byte order, and in ones-compliment
"obfuscated" form the same as described in Section 12.2.4.
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o Proxy/Server ULA/INADDR includes a 15 octet value that
encodes the 120 least significant bits of the Proxy/Server
ULA followed by a 16 octet INADDR. (Note that the FMT/SRT
code is replaced with the value "fd" after processing to
form a proper Proxy/Server ULA.) INADDR identifies an open
INET interface not located behind NATs, therefore no UDP
port number is included since port number 8060 is used when
the L2 encapsulation includes a UDP header.
o Gateway ULA/INADDR encodes a 16 octet ULA followed by a 16
octet INADDR exactly as for the Proxy/Server ULA/INADDR.
(Note that the Gateway ULA simply encodes the value "fd" in
the most significant bits, since the FMT/SRT code applies to
both the Proxy/Server and Gateway.)
12.2.6. Traffic Selector
When used in conjunction with Interface Attributes and/or Multilink
Forwarding Parameters information, the Traffic Selector sub-option
provides forwarding information for the multilink conceptual sending
algorithm discussed in Section 14.
IPv6 ND messages include Traffic Selectors for some or all of the
source/target Client's underlay interfaces. Traffic Selectors for
some or all of a target Client's underlay interfaces are also
included in uNA messages used to publish Client information changes.
See: [I-D.templin-6man-aero] for more information.
Traffic Selectors must be honored by all implementations in the
format shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=5| Sub-length=N | omIndex | TS Format |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ RFC 6088 Format Traffic Selector ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: Traffic Selector
* Sub-Type is set to 5. Each IPv6 ND message may contain zero or
more Traffic Selectors for each omIndex; when multiple Traffic
Selectors for the same omIndex appear, all are processed and the
cumulative information from all is accepted.
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* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
* Sub-Option Data contains a "Traffic Selector" encoded as follows:
- omIndex is a 1-octet value corresponding to a specific underlay
interface the same as specified above for Interface Attributes
and Multilink Forwarding Parameters above. The OMNI options of
a single message may include multiple Traffic Selector sub-
options; each with the same or different omIndex values.
- TS Format is a 1-octet field that encodes a Traffic Selector
version per [RFC6088]. If TS Format encodes the value 1 or 2,
the Traffic Selector includes IPv4 or IPv6 information,
respectively. If TS Format encodes any other value, the sub-
option is ignored.
- The remainder of the sub-option includes a traffic selector
formatted per [RFC6088] beginning with the "Flags (A-N)" field,
and with the Traffic Selector IP protocol version coded in the
TS Format field. If a single interface identified by omIndex
requires Traffic Selectors for multiple IP protocol versions,
or if a Traffic Selector block would exceed the available
space, the remaining information is coded in additional Traffic
Selector sub-options that all encode the same omIndex.
12.2.7. Geo Coordinates
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=6| Sub-length=N | Geo Type |Geo Coordinates
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 21: Geo Coordinates Sub-option
* Sub-Type is set to 6. If multiple instances appear in OMNI
options of the same message all are processed.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
* Geo Type is a 1 octet field that encodes a type designator that
determines the format and contents of the Geo Coordinates field
that follows. The following types are currently defined:
- 0 - NULL, i.e., the Geo Coordinates field is zero-length.
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* A set of Geo Coordinates of length up to the remaining available
space for this OMNI option. New formats to be specified in future
documents and may include attributes such as latitude/longitude,
altitude, heading, speed, etc.
12.2.8. Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Message
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) sub-option
may be included in the OMNI options of Client RS messages and Proxy/
Server RA messages. FHS Proxy/Servers that forward RS/RA messages
between a Client and an LHS Proxy/Server also forward DHCPv6 Sub-
Options unchanged. Note that DHCPv6 messages do not include a
Checksum field since integrity is protected by the IPv6 ND message
checksum, authentication signature and/or lower-layer authentication
and integrity checks.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=7| Sub-length=N | msg-type | id (octet 0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| transaction-id (octets 1-2) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
. DHCPv6 options .
. (variable number and length) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: DHCPv6 Message Sub-option
* Sub-Type is set to 7. If multiple instances appear in OMNI
options of the same message the first is processed and all others
are ignored.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The 'msg-type' and 'transaction-id' fields
are always present; hence, the length of the DHCPv6 options is
limited by the remaining available space for this OMNI option.
* 'msg-type' and 'transaction-id' are coded according to Section 8
of [RFC8415].
* A set of DHCPv6 options coded according to Section 21 of [RFC8415]
follows.
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12.2.9. Host Identity Protocol (HIP) Message
The Host Identity Protocol (HIP) Message sub-option (when present)
provides authentication for IPv6 ND messages exchanged between
Clients and FHS Proxy/Servers over an open Internetwork. FHS Proxy/
Servers authenticate the HIP authentication signatures in source
Client IPv6 ND messages before securely forwarding them to other OMNI
nodes. LHS Proxy/Servers that receive secured IPv6 ND messages from
other OMNI nodes that do not already include a security sub-option
insert HIP authentication signatures before forwarding them to the
target Client.
OMNI interfaces MUST include the HIP message (when present) as the
first sub-option of the first OMNI option, which MUST appear
immediately following the IPv6 ND message header. OMNI interfaces
can therefore easily locate the HIP message and verify the
authentication signature without applying deep inspection. OMNI
interfaces that receive IPv6 ND messages without a HIP (or other
authentication) sub-option as the first OMNI sub-option instead
verify the IPv6 ND message checksum.
OMNI interfaces include the HIP message sub-option when they forward
IPv6 ND messages that require security over INET underlay interfaces,
i.e., where authentication and integrity is not already assured by
lower layers. The OMNI interface calculates the authentication
signature over the entire length of the OAL packet (or super-packet)
beginning with a pseudo-header of the IPv6 ND message header and
extending over the remainder of the OAL packet. OMNI interfaces that
process OAL packets that contain secured IPv6 ND messages verify the
signature then either process the rest of the message locally or
forward a proxyed copy to the next hop.
When a FHS Client inserts a HIP message sub-option in an NS/NA
message destined to a target in a remote spanning tree segment, it
must ensure that the insertion does not cause the message to exceed
the OMNI interface MTU. When the remote segment LHS Proxy/Server
forwards the NS/NA message from the spanning tree to the target
Client, it inserts a new HIP message sub-option if necessary while
overwriting or cancelling the (now defunct) HIP message sub-option
supplied by the FHS Client.
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If the defunct HIP sub-option size was smaller than the space needed
for the LHS Client HIP message (or, if no defunct HIP sub-option is
present), the LHS Proxy/Server adjusts the space immediately
following the OMNI header by copying the preceding portion of the
IPv6 ND message into buffer headroom free space or copying the
remainder of the IPv6 ND message into buffer tailroom free space.
The LHS Proxy/Server then insets the new HIP sub-option immediately
after the OMNI header and immediately before the next sub-option
while properly overwriting the defunct sub-option if present.
If the defunct HIP sub-option size was larger than the space needed
for the LHS Client HIP message, the LHS Proxy/Server instead
overwrites the existing sub-option and writes a single Pad1 or PadN
sub-option over the next 1-2 octets to cancel the remainder of the
defunct sub-option. If the LHS Proxy/Server cannot create sufficient
space through any means without causing the OMNI option to exceed
2040 octets or causing the IPv6 ND message to exceed the OMNI
interface MTU, it returns a suitable error (see: Section 12.2.13) and
drops the message.
The HIP message sub-option is formatted as shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=8| Sub-length=N |0| Packet Type |Version| RES.|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Controls |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ HIP Parameters /
/ /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23: HIP Message Sub-option
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* Sub-Type is set to 8. If multiple instances appear in OMNI
options of the same message the first is processed and all others
are ignored.
* Sub-Length is set to N, i.e., the length of the option in octets
beginning immediately following the Sub-Length field and extending
to the end of the HIP parameters. The length of the entire HIP
message is therefore limited by the remaining available space for
this OMNI option.
* The HIP message is coded per Section 5 of [RFC7401], except that
the OMNI "Sub-Type" and "Sub-Length" fields replace the first 2
octets of the HIP message header (i.e., the Next Header and Header
Length fields). Also, since the IPv6 ND message is already
protected by the authentication signature and/or lower-layer
authentication and integrity checks, the HIP message Checksum
field is replaced by a Reserved field set to 0 on transmission and
ignored on reception.
Note: In some environments, maintenance of a Host Identity Tag (HIT)
namespace may be unnecessary for securely associating an OMNI node
with an IPv6 address-based identity. In that case, IPv6 ULAs can be
used instead of HITs in the authentication signature as long as the
address can be uniquely associated with the Sender/Receiver.
12.2.10. PIM-SM Message
The Protocol Independent Multicast - Sparse Mode (PIM-SM) Message
sub-option may be included in the OMNI options of IPv6 ND messages.
PIM-SM messages are formatted as specified in Section 4.9 of
[RFC7761], with the exception that the Checksum field is replaced by
a Reserved field (set to 0) since the IPv6 ND message is already
protected by the IPv6 ND message checksum, authentication signature
and/or lower-layer authentication and integrity checks. The PIM-SM
message sub-option format is shown in Figure 24:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S-Type=9| Sub-length=N |PIM Ver| Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ PIM-SM Message /
/ /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 24: PIM-SM Message Option Format
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* Sub-Type is set to 9. If multiple instances appear in OMNI
options of the same message all are processed.
* Sub-Length is set to N, i.e., the length of the option in octets
beginning immediately following the Sub-Length field and extending
to the end of the PIM-SM message. The length of the entire PIM-SM
message is therefore limited by the remaining available space for
this OMNI option.
* The PIM-SM message is coded exactly as specified in Section 4.9 of
[RFC7761], except that the Checksum field is replaced by a
Reserved field set to 0 on transmission and ignored on reception.
The "PIM Ver" field MUST encode the value 2, and the "Type" field
encodes the PIM message type. (See Section 4.9 of [RFC7761] for a
list of PIM-SM message types and formats.)
12.2.11. Fragmentation Report (FRAGREP)
Fragmentation Report (FRAGREP) sub-options may be included in the
OMNI options of uNA messages sent from an OAL destination to an OAL
source. The message consists of (N / 20)-many (Identification,
Bitmap)-tuples which include the Identification values of OAL
fragments received plus a Bitmap marking the ordinal positions of
individual fragments received and fragments missing.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=10| Sub-Length = N | Identification #1 (bits 0-15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification #1 (bits 15-31)| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
| Bitmap #1 (bits 0 - 127) |
~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Identification #2 (bits 0-15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification #2 (bits 15-31)| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Bitmap #2 (bits 0 - 127) |
~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
| ... |
+ ... +
Figure 25: Fragmentation Report (FRAGREP)
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* Sub-Type is set to 10. If multiple instances appear in OMNI
options of the same message all are processed.
* Sub-Length is set to N, i.e., the length of the option in octets
beginning immediately following the Sub-Length field and extending
to the end of the sub-option. If N is not an integral multiple of
20 octets, the sub-option is ignored. The length of the entire
sub-option should not cause the entire IPv6 ND message to exceed
the minimum IPv6 MTU.
* Identification (i) includes the IPv6 Identification value found in
the Fragment Header of a received OAL fragment. (Only those
Identification values included represent fragments for which loss
was unambiguously observed; any Identification values not included
correspond to fragments that were either received in their
entirety or may still be in transit.)
* Bitmap (i) includes an ordinal checklist of up to 128 fragments,
with each bit set to 1 for a fragment received or 0 for a fragment
missing. For example, for a 20-fragment OAL packet with ordinal
fragments #3, #10, #13 and #17 missing and all other fragments
received, Bitmap (i) encodes the following:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|1|1|1|0|1|1|1|1|1|1|0|1|1|0|1|1|1|0|1|1|0|0|0|...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 26
(Note that loss of an OAL atomic fragment is indicated by a
Bitmap(i) with all bits set to 0.)
12.2.12. Node Identification
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=11| Sub-length=N | ID-Type | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ Node Identification Value (N-1 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 27: Node Identification
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* Sub-Type is set to 11. If multiple instances appear in OMNI
options of the same IPv6 ND message the first instance of a
specific ID-Type is processed and all other instances of the same
ID-Type are ignored. (It is therefore possible for a single IPv6
ND message to convey multiple distinct Node Identifications - each
with a different ID-Type.)
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The ID-Type field is always present; hence,
the maximum Node Identification Value length is limited by the
remaining available space in this OMNI option.
* ID-Type is a 1 octet field that encodes the type of the Node
Identification Value. The following ID-Type values are currently
defined:
- 0 - Universally Unique IDentifier (UUID) [RFC4122]. Indicates
that Node Identification Value contains a 16 octet UUID.
- 1 - Host Identity Tag (HIT) [RFC7401]. Indicates that Node
Identification Value contains a 16 octet HIT.
- 2 - Hierarchical HIT (HHIT) [I-D.ietf-drip-rid]. Indicates
that Node Identification Value contains a 16 octet HHIT.
- 3 - Network Access Identifier (NAI) [RFC7542]. Indicates that
Node Identification Value contains an N-1 octet NAI.
- 4 - Fully-Qualified Domain Name (FQDN) [RFC1035]. Indicates
that Node Identification Value contains an N-1 octet FQDN.
- 5 - IPv6 Address. Indicates that Node Identification contains
a 16-octet IPv6 address that is not a (H)HIT. The IPv6 address
type is determined according to the IPv6 addressing
architecture [RFC4291].
- 6 - 252 - Unassigned.
- 253-254 - Reserved for experimentation, as recommended in
[RFC3692].
- 255 - reserved by IANA.
* Node Identification Value is an (N - 1) octet field encoded
according to the appropriate the "ID-Type" reference above.
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OMNI interfaces code Node Identification Values used for DHCPv6
messaging purposes as a DHCP Unique IDentifier (DUID) using the
"DUID-EN for OMNI" format with enterprise number 45282 (see:
Section 25) as shown in Figure 28:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DUID-Type (2) | EN (high bits == 0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EN (low bits = 45282) | ID-Type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ Node Identification Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 28: DUID-EN for OMNI Format
In this format, the OMNI interface codes the ID-Type and Node
Identification Value fields from the OMNI sub-option following a 6
octet DUID-EN header, then includes the entire "DUID-EN for OMNI" in
a DHCPv6 message per [RFC8415].
12.2.13. ICMPv6 Error
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=12| Sub-length=N | Type | Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Message Body +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 29: ICMPv6 Error
* Sub-Type is set to 12. If multiple instances appear in OMNI
options of the same IPv6 ND message all are processed.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
* Sub-Option Data includes a one octet Type followed by a one octet
Code followed by an (N-2)-octet Message Body encoded exactly as
per Section 2.1 of [RFC4443]. OMNI interfaces include as much of
the ICMPv6 error message body in the sub-option as possible
without causing the entire IPv6 ND message to exceed the minimum
IPv6 MTU. While all ICMPv6 error message types are supported, OAL
destinations in particular may include ICMPv6 PTB messages in uNA
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messages to provide MTU feedback information via the OAL source
(see: Section 6.8). Note: ICMPv6 informational messages must not
be included and must be ignored if received.
12.2.14. QUIC-TLS Message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=13| Sub-length=N | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ~
~ QUIC-TLS Message ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 30: QUIC-TLS Message
* Sub-Type is set to 13. If multiple instances appear in OMNI
options of the same IPv6 ND message, the first is processed and
all others are ignored.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow.
* The QUIC-TLS message [RFC9000][RFC9001][RFC9002] encodes the QUIC
and TLS message parameters necessary to support QUIC connection
establishment.
When present, the QUIC-TLS Message sub-option MUST appear immediately
after the header of the first OMNI option in the IPv6 ND message; if
the sub-option appears in any other location it MUST be ignored.
IPv6 ND solicitation and advertisement messages serve as couriers to
transport the QUIC and TLS parameters necessary to establish a
secured QUIC connection.
12.2.15. Proxy/Server Departure
OMNI Clients include a Proxy/Server Departure sub-option in RS
messages when they associate with a new FHS and/or Hub Proxy/Server
and need to send a departure indication to an old FHS and/or Hub
Proxy/Server. The Proxy/Server Departure sub-option is formatted as
shown below:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=14| Sub-length=32 | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ Old FHS Proxy/Server ULA (16 octets) ~
~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ Old Hub Proxy/Server ULA (16 0ctets) ~
~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 31: Proxy/Server Departure
* Sub-Type is set to 14.
* Sub-Length is set to 32.
* Sub-Option Data contains the 16 octet ULA for the "Old FHS Proxy/
Server" followed by a 16 octet ULA for an "Old Hub Proxy/Server.
(If the Old FHS/Hub is unspecified, the corresponding ULA instead
includes the value 0.)
12.2.16. Sub-Type Extension
Since the Sub-Type field is only 5 bits in length, future
specifications of major protocol functions may exhaust the remaining
Sub-Type values available for assignment. This document therefore
defines Sub-Type 30 as an "extension", meaning that the actual Sub-
Option type is determined by examining a 1 octet "Extension-Type"
field immediately following the Sub-Length field. The Sub-Type
Extension is formatted as shown in Figure 32:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Extension-Type| ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ ~
~ Extension-Type Body ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 32: Sub-Type Extension
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* Sub-Type is set to 30. If multiple instances appear in OMNI
options of the same message all are processed, where each
individual extension defines its own policy for processing
multiple of that type.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The Extension-Type field is always present,
and the maximum Extension-Type Body length is limited by the
remaining available space in this OMNI option.
* Extension-Type contains a 1 octet Sub-Type Extension value between
0 and 255.
* Extension-Type Body contains an N-1 octet block with format
defined by the given extension specification.
Extension-Type values 0 and 1 are defined in the following
subsections, while Extension-Type values 2 through 252 are available
for assignment by future specifications which must also define the
format of the Extension-Type Body and its processing rules.
Extension-Type values 253 and 254 are reserved for experimentation,
as recommended in [RFC3692], and value 255 is reserved by IANA.
12.2.16.1. RFC4380 Header Extension Option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Ext-Type=0 | Header Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Header Option Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 33: RFC4380 Header Extension Option (Extension-Type 0)
* Sub-Type is set to 30.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The Extension-Type and Header Type fields are
always present, and the Header Option Value is limited by the
remaining available space in this OMNI option.
* Extension-Type is set to 0. Each instance encodes exactly one
header option per Section 5.1.1 of [RFC4380], with Ext-Type and
Header Type representing the first two octets of the option. If
multiple instances of the same Header Type appear in OMNI options
of the same message the first instance is processed and all others
are ignored. If Header Type indicates an Authentication
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Encapsulation (see below), the entire sub-option MUST appear as
the first sub-option of the first OMNI option, which MUST appear
immediately following the IPv6 ND message header.
* Header Type and Header Option Value are coded exactly as specified
in Section 5.1.1 of [RFC4380]; the following types are currently
defined:
- 0 - Origin Indication (IPv4) - value coded as a UDP port number
followed by a 4-octet IPv4 address both in "obfuscated" form
per Section 5.1.1 of [RFC4380].
- 1 - Authentication Encapsulation - value coded per
Section 5.1.1 of [RFC4380].
- 2 - Origin Indication (IPv6) - value coded per Section 5.1.1 of
[RFC4380], except that the address is a 16-octet IPv6 address
instead of a 4-octet IPv4 address.
* Header Type values 3 through 252 are available for assignment by
future specifications, which must also define the format of the
Header Option Value and its processing rules. Header Type values
253 and 254 are reserved for experimentation, as recommended in
[RFC3692], and value 255 is Reserved by IANA.
12.2.16.2. RFC6081 Trailer Extension Option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S-Type=30| Sub-length=N | Ext-Type=1 | Trailer Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Trailer Option Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 34: RFC6081 Trailer Extension Option (Extension-Type 1)
* Sub-Type is set to 30.
* Sub-Length is set to N that encodes the number of Sub-Option Data
octets that follow. The Extension-Type and Trailer Type fields
are always present, and the maximum-length Trailer Option Value is
limited by the remaining available space in this OMNI option.
* Extension-Type is set to 1. Each instance encodes exactly one
trailer option per Section 4 of [RFC6081]. If multiple instances
of the same Trailer Type appear in OMNI options of the same
message the first instance is processed and all others ignored.
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* Trailer Type and Trailer Option Value are coded exactly as
specified in Section 4 of [RFC6081]; the following Trailer Types
are currently defined:
- 0 - Unassigned
- 1 - Nonce Trailer - value coded per Section 4.2 of [RFC6081].
- 2 - Unassigned
- 3 - Alternate Address Trailer (IPv4) - value coded per
Section 4.3 of [RFC6081].
- 4 - Neighbor Discovery Option Trailer - value coded per
Section 4.4 of [RFC6081].
- 5 - Random Port Trailer - value coded per Section 4.5 of
[RFC6081].
- 6 - Alternate Address Trailer (IPv6) - value coded per
Section 4.3 of [RFC6081], except that each address is a
16-octet IPv6 address instead of a 4-octet IPv4 address.
* Trailer Type values 7 through 252 are available for assignment by
future specifications, which must also define the format of the
Trailer Option Value and its processing rules. Trailer Type
values 253 and 254 are reserved for experimentation, as
recommended in [RFC3692], and value 255 is Reserved by IANA.
13. Address Mapping - Multicast
The multicast address mapping of the native underlay interface
applies. The Client mobile router also serves as an IGMP/MLD Proxy
for its ENETs and/or hosted applications per [RFC4605].
The Client uses Multicast Listener Discovery (MLDv2) [RFC3810] to
coordinate with Proxy/Servers, and underlay network elements use MLD
snooping [RFC4541]. The Client can also employ multicast routing
protocols to coordinate with network-based multicast sources as
specified in [I-D.templin-6man-aero].
Since the OMNI link model is NBMA, OMNI links support link-scoped
multicast through iterative unicast transmissions to individual
multicast group members (i.e., unicast/multicast emulation).
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14. Multilink Conceptual Sending Algorithm
The Client's IPv6 layer selects the outbound OMNI interface according
to SBM considerations when forwarding original IP packets from local
or ENET applications to external correspondents. Each OMNI interface
maintains a neighbor cache the same as for any IPv6 interface, but
includes additional state for multilink coordination. Each Client
OMNI interface maintains default routes via Proxy/Servers discovered
as discussed in Section 15, and may configure more-specific routes
discovered through means outside the scope of this specification.
For each original IP packet it forwards, the OMNI interface selects
one or more source underlay interfaces based on PBM factors (e.g.,
traffic attributes, cost, performance, message size, etc.) and one or
more target underlay interfaces for the neighbor based on Interface
Attributes received in IPv6 ND messages (see: Section 12.2.4).
Multilink forwarding may also direct packet replication across
multiple underlay interface pairs for increased reliability at the
expense of duplication. The set of all Interface Attributes and
Traffic Selectors received in IPv6 ND messages determines the
multilink forwarding profile for selecting target underlay
interfaces.
When the OMNI interface sends an original IP packet over a selected
source underlay interface, it first employs OAL encapsulation and
fragmentation as discussed in Section 5, then performs L2
encapsulation as directed by the appropriate MFV. The OMNI interface
also performs L2 encapsulation (following OAL encapsulation) when the
nearest Proxy/Server is located multiple hops away as discussed in
Section 15.2.
OMNI interface multilink service designers MUST observe the BCP
guidance in Section 15 [RFC3819] in terms of implications for
reordering when original IP packets from the same flow may be spread
across multiple underlay interfaces having diverse properties.
14.1. Multiple OMNI Interfaces
Clients may connect to multiple independent OMNI links within the
same or different OMNI domains to support SBM. The Client configures
a separate OMNI interface for each link so that multiple interfaces
(e.g., omni0, omni1, omni2, etc.) are exposed to the IP layer. Each
OMNI interface configures one or more OMNI anycast addresses (see:
Section 10), and the Client injects the corresponding anycast
prefixes into the ENET routing system. Multiple distinct OMNI links
can therefore be used to support fault tolerance, load balancing,
reliability, etc.
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Applications in ENETs can use Segment Routing to select the desired
OMNI interface based on SBM considerations. The application writes
an OMNI anycast address into the original IP packet's destination
address, and writes the actual destination (along with any additional
intermediate hops) into the Segment Routing Header. Standard IP
routing directs the packet to the Client's mobile router entity,
where the anycast address identifies the correct OMNI interface for
next hop forwarding. When the Client receives the packet, it
replaces the IP destination address with the next hop found in the
Segment Routing Header and forwards the message via the OMNI
interface identified by the anycast address.
Note: The Client need not configure its OMNI interface indexes in
one-to-one correspondence with the global OMNI Link-IDs configured
for OMNI domain administration since the Client's indexes (i.e.,
omni0, omni1, omni2, etc.) are used only for its own local interface
management.
14.2. Client-Proxy/Server Loop Prevention
After a Proxy/Server has registered an MNP for a Client (see:
Section 15), the Proxy/Server will forward all packets destined to an
address within the MNP to the Client. The Client will under normal
circumstances then forward the packet to the correct destination
within its connected (downstream) ENETs.
If at some later time the Client loses state (e.g., after a reboot),
it may begin returning packets with destinations corresponding to its
MNP to the Proxy/Server as its default router. The Proxy/Server
therefore drops any original IP packets received from the Client with
a destination address that corresponds to the Client's MNP (i.e.,
whether ULA or GUA), and drops any carrier packets with both source
and destination address corresponding to the same Client's MNP
regardless of their origin.
15. Router Discovery and Prefix Registration
Clients engage the MS by sending RS messages with OMNI options under
the assumption that one or more Proxy/Server will process the message
and respond. The RS message is received by a FHS Proxy/Server, which
may in turn forward a proxyed copy of the RS to a Hub Proxy/Server
located on the same or different SRT segment. The Hub Proxy/Server
then returns an RA message either directly to the Client or via an
FHS Proxy/Server acting as a proxy.
Clients and FHS Proxy/Servers include an authentication signature in
their RS/RA exchanges when necessary; otherwise, they calculate and
include a valid IPv6 ND message checksum (see: Section 12 and
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Appendix B). FHS and Hub Proxy/Server RS/RA message exchanges over
the SRT secured spanning tree instead always include the checksum and
omit the authentication signature. Clients and Proxy/Servers use the
information included in RS/RA messages to establish NCE state and
OMNI link autoconfiguration information as discussed in this section.
For each underlay interface, the Client sends RS messages with OMNI
options to coordinate with a (potentially) different FHS Proxy/Server
for each interface but with a single Hub Proxy/Server. All Proxy/
Servers are identified by their ADM-ULAs and accept carrier packets
addressed to their anycast/unicast L2 INADDRs; the Hub Proxy/Server
may be chosen among any of the Client's FHS Proxy/Servers or may be
any other Proxy/Server for the OMNI link. Example ULA/INADDR
discovery methods are given in [RFC5214] and include data link login
parameters, name service lookups, static configuration, a static
"hosts" file, etc. In the absence of other information, the Client
can resolve the DNS Fully-Qualified Domain Name (FQDN)
"linkupnetworks.[domainname]" where "linkupnetworks" is a constant
text string and "[domainname]" is a DNS suffix for the OMNI link
(e.g., "example.com"). The name resolution will retain a set of DNS
resource records with the addresses of Proxy/Servers for the domain.
Each FHS Proxy/Server configures an ADM-ULA based on a /64 ULA prefix
for the link/segment with randomly-generated Global ID to assure
global uniqueness then administratively assigned to FHS Proxy/Servers
for the link to assure global consistency. The Client can then
configure MNP-ULAs derived from the 64-bit ULA prefix assigned to a
FHS Proxy/Server for each underlay interface. The FHS Proxy/Servers
discovered over multiple of the Client's underlay interfaces may
configure the same or different ULA prefixes, and the Client's MNP-
ULA for each underlay interface will fall within the ULA (multilink)
subnet relative to each FHS Proxy/Server.
Clients configure OMNI interfaces that observe the properties
discussed in previous sections. The OMNI interface and its underlay
interfaces are said to be in either the "UP" or "DOWN" state
according to administrative actions in conjunction with the interface
connectivity status. An OMNI interface transitions to UP or DOWN
through administrative action and/or through state transitions of the
underlay interfaces. When a first underlay interface transitions to
UP, the OMNI interface also transitions to UP. When all underlay
interfaces transition to DOWN, the OMNI interface also transitions to
DOWN.
When a Client OMNI interface transitions to UP, it sends RS messages
to register its MNP and an initial set of underlay interfaces that
are also UP. The Client sends additional RS messages to refresh
lifetimes and to register/deregister underlay interfaces as they
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transition to UP or DOWN. The Client's OMNI interface sends initial
RS messages over an UP underlay interface with its MNP-XLA as the
source (or with a random TMP-ULA as the source if it does not yet
have an MNP) and with destination set to link-scoped All-Routers
multicast or the ADM-ULA of a specific (Hub) Proxy/Server. The OMNI
interface includes an OMNI option per Section 12 with an OMNI
Neighbor Coordination sub-option with (Preflen assertion, N/A/U flags
and Window Synchronization parameters), an Interface Attributes sub-
option for the underlay interface, a DHCPv6 Solicit sub-option if
necessary, and with any other necessary OMNI sub-options such as
authentication, Proxy/Server Departure, etc.
The Client then calculates the authentication signature or checksum
and prepares to forward the RS over the underlay interface using OAL
encapsulation and fragmentation if necessary. If the Client uses OAL
encapsulation for RS messages sent to an unsynchronized FHS Proxy/
Server over an INET interface, the entire RS message must fit within
a single carrier packet (i.e., an atomic fragment) so that the FHS
Proxy/Server can verify the authentication signature without having
to reassemble. The OMNI interface selects an Identification value
(see: Section 6.6), sets the OAL source address to the MNP-ULA
corresponding to the RS source if known (otherwise to a TMP-ULA),
sets the OAL destination to an OMNI IPv6 anycast or ADM-ULA unicast
address, optionally includes a Nonce and/or Timestamp, then performs
fragmentation if necessary. When L2 encapsulation is used, the
Client includes the discovered FHS Proxy/Server INADDR or an anycast
address as the L2 destination then forwards the resulting carrier
packet(s) into the underlay network. Note that the Client does not
yet create a NCE, but instead remembers the Identification, Nonce
and/or Timestamp values included in its RS message transmissions to
match against any received RA messages.
When an FHS Proxy/Server receives the carrier packets containing an
RS it sets aside the L2 headers, verifies the Identifications and
reassembles if necessary, sets aside the OAL header, then verifies
the RS authentication signature or checksum. The FHS Proxy/Server
then creates/updates a NCE indexed by the Client's RS source address
and caches the OMNI Interface Attributes and any Traffic Selector
sub-options while also caching the L2 (UDP/IP) and OAL (ULA) source
and destination address information. The FHS Proxy/Server next
caches the OMNI Neighbor Coordination sub-option Window
Synchronization parameters and N flag to determine its role in
processing NS(NUD) messages (see: Section 12.1) then examines the RS
destination address. If the destination matches its own ADM-ULA, the
FHS Proxy/Server assumes the Hub role and acts as the sole entry
point for injecting the Client's MNP-XLA into the MS routing system
(i.e., after performing any necessary prefix delegation operations)
while including a prefix length and setting the prefix to fd00::/64
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and suffix to the 64-bit MNP. The FHS/Hub Proxy/Server then caches
the OMNI Neighbor Coordination sub-option A/U flags to determine its
role in processing NS(AR) messages and generating uNA messages (see:
Section 12.1).
The FHS/Hub Proxy/Server then prepares to return an RA message
directly to the Client by first populating the Cur Hop Limit, Flags,
Router Lifetime, Reachable Time and Retrans Timer fields with values
appropriate for the OMNI link. The FHS/Hub Proxy/Server next
includes as the first RA message option an OMNI option with a
neighbor coordination sub-option with Window Synchronization
information, an authentication sub-option if necessary and a
(proxyed) copy of the Client's original Interface Attributes sub-
option with its INET-facing interface information written in the FMT/
SRT and LHS Proxy/Server ULA/INADDR fields. If the RS L2 destination
IP address was anycast, the FHS/Hub Proxy/Server next includes a
second Interface Attributes sub-option with omIndex set to '0' and
with a unicast L2 IP address for its Client-facing interface in the
INADDR field.
The FHS/Hub Proxy/Server next includes an Origin Indication sub-
option that includes the RS L2 source INADDR information (see:
Section 12.2.16.1), then includes any other necessary OMNI sub-
options (either within the same OMNI option or in additional OMNI
options). Following the OMNI option(s), the FHS/Hub Proxy/Server
next includes any other necessary RA options such as PIOs with (A;
L=0) that include the OMNI link MSPs [RFC8028], RIOs [RFC4191] with
more-specific routes, Nonce and Timestamp options, etc. The FHS/Hub
Proxy/Server then sets the RA source address to its own ADM-ULA and
destination address to the Client's MNP-ULA (i.e., relative to the
ULA /64 prefix for its Client-facing underlay interface) while also
recording the MNP-XLA as an (alternate) index to the Client NCE, then
calculates the authentication signature or checksum. The FHS/Hub
Proxy/Server finally performs OAL encapsulation with source set to
its own ADM-ULA and destination set to the OAL source that appeared
in the RS, then fragments if necessary, encapsulates each fragment in
appropriate L2 headers with source and destination address
information reversed from the RS L2 information and returns the
resulting carrier packets to the Client over the same underlay
interface the RS arrived on.
When an FHS Proxy/Server receives an RS with a valid authentication
signature or checksum and with destination set to link-scoped All-
Routers multicast, it can either assume the Hub role itself the same
as above or act as a proxy and select the ADM-ULA of another Proxy/
Server to serve as the Hub. When an FHS Proxy/Server assumes the
proxy role or receives an RS with destination set to the ADM-ULA of
another Proxy/Server, it forwards the message while acting as a
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proxy. The FHS Proxy/Server creates/updates a NCE for the Client
(i.e., based on the RS source address) and caches the OAL source,
Window Synchronization, N flag, Interface Attributes addressing
information as above then writes its own INET-facing FMT/SRT and LHS
Proxy/Server ULA/INADDR information into the appropriate Interface
Attributes sub-option fields. The FHS Proxy/Server then calculates
and includes the checksum, performs OAL encapsulation with source set
to its own ADM-ULA and destination set to the ADM-ULA of the Hub
Proxy/Server, fragments if necessary, encapsulates each fragment in
appropriate L2 headers and sends the resulting carrier packets into
the SRT secured spanning tree.
When the Hub Proxy/Server receives the carrier packets, it discards
the L2 headers, reassembles if necessary to obtain the proxyed RS,
then performs DHCPv6 Prefix Delegation (PD) to obtain the Client's
MNP if the RS source is a TMP-ULA. The Hub Proxy/Server then
creates/updates a NCE for the Client's MNP-XLA and caches any state
(including the A/U flags, OAL addresses, Interface Attributes
information and Traffic Selectors), then finally performs routing
protocol injection. The Hub Proxy/Server then returns an RA that
echoes the Client's (proxyed) Interface Attributes sub-option and
with any RA parameters the same as specified for the FHS/Hub Proxy/
Server case above. The Hub Proxy/Server then sets the RA source
address to its own ADM-ULA and destination address to the RS source
address; if the RS source address is a TMP-ULA, the Hub Proxy/Server
also includes the MNP in a DHCPv6 PD Reply OMNI sub-option. The Hub
Proxy/Server next calculates the checksum, then encapsulates the RA
as an OAL packet with source set to its own ADM-ULA and destination
set to the ADM-ULA of the FHS Proxy/Server that forwarded the RS.
The Hub Proxy/Server finally fragments if necessary, encapsulates
each fragment in appropriate L2 headers and sends the resulting
carrier packets into the secured spanning tree.
When the FHS Proxy/Server receives the carrier packets it discards
the L2 headers, reassembles if necessary to obtain the RA message,
verifies the checksum then updates the OMNI interface NCE for the
Client and creates/updates a NCE for the Hub. The FHS Proxy/Server
then sets the P flag in the RA flags field [RFC4389] and proxys the
RA by changing the OAL source to its own ADM-ULA, changing the OAL
destination to the OAL address found in the Client's NCE, and
changing the RA destination address to the MNP-ULA of the Client
relative to its own /64 ULA prefix while also recording the MNP-XLA
as an alternate index into the Client NCE. (If the RA destination
address was a TMP-ULA, the FHS Proxy Server determines the MNP by
consulting the DHCPv6 PD Reply message sub-option.) The FHS Proxy/
Server next includes Window Synchronization parameters responsive to
those in the Client's RS, an Interface Attributes sub-option with
omIndex '0' and with its unicast L2 IP address if necessary (see
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above), an Origin Indication sub-option with the Client's cached
INADDR and an authentication sub-option if necessary. The FHS Proxy/
Server finally selects an Identification value per Section 6.6,
calculates the authentication signature or checksum, fragments if
necessary, encapsulates each fragment in L2 headers with addresses
taken from the Client's NCE and returns the resulting carrier packets
via the same underlay interface over which the RS was received.
When the Client receives the carrier packets, it discards the L2
headers, reassembles if necessary and removes the OAL header to
obtain the RA message. The Client next verifies the authentication
signature or checksum, then matches the RA message with its
previously-sent RS by comparing the RS Sequence Number with the RA
Acknowledgement Number and also comparing the Nonce and/or Timestamp
values if present. If the values match, the Client then creates/
updates OMNI interface NCEs for both the Hub and FHS Proxy/Server and
caches the information in the RA message. In particular, the Client
caches the RA source address as the Hub Proxy/Server ADM-ULA and uses
the OAL source address to configure both an underlay interface-
specific ADM-ULA for the Hub Proxy/Server and the ADM-ULA of this FHS
Proxy/Server. The Client then uses the MNP-ULA in the RA destination
address to configure its address within the ULA (multilink) subnet
prefix of the FHS Proxy/Server. If the Client has multiple underlay
interfaces, it creates additional FHS Proxy/Server NCEs and MNP-ULAs
as necessary when it receives RAs over those interfaces (noting that
multiple of the Client's underlay interfaces may be serviced by the
same or different FHS Proxy/Servers). The Client finally adds the
Hub Proxy/Server ADM-ULA to the default router list if necessary.
For each underlay interface, the Client next caches the (filled-out)
Interface Attributes for its own omIndex and Origin Indication
information that it received in an RA message over that interface so
that it can include them in future NS/NA messages to provide
neighbors with accurate FMT/SRT/LHS information. (If the message
includes an Interface Attributes sub-option with omIndex '0', the
Client also caches the INADDR as the underlay network-local unicast
address of the FHS Proxy//Server via that underlay interface.) The
Client then compares the Origin Indication INADDR information with
its own underlay interface addresses to determine whether there may
be NATs on the path to the FHS Proxy/Server; if the INADDR
information differs, the Client is behind a NAT and must supply the
Origin information in IPv6 ND message exchanges with prospective
neighbors on the same SRT segment. The Client finally configures
default routes and assigns the OMNI Subnet Router Anycast address
corresponding to the MNP (e.g., 2001:db8:1:2::) to the OMNI
interface.
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Following the initial exchange, the FHS Proxy/Server MAY later send
additional periodic and/or event-driven unsolicited RA messages per
[RFC4861]. (The unsolicited RAs may be initiated either by the FHS
Proxy/Server itself or by the Hub via the FHS as a proxy.) The
Client then continuously manages its underlay interfaces according to
their states as follows:
* When an underlay interface transitions to UP, the Client sends an
RS over the underlay interface with an OMNI option with sub-
options as specified above.
* When an underlay interface transitions to DOWN, the Client sends
unsolicited NA messages over any UP underlay interface with an
OMNI option containing Interface Attributes sub-options for the
DOWN underlay interface with Link set to '0'. The Client sends
isolated unsolicited NAs when reliability is not thought to be a
concern (e.g., if redundant transmissions are sent on multiple
underlay interfaces), or may instead set the PNG flag in the OMNI
header to trigger a uNA reply.
* When the Router Lifetime for the Hub Proxy/Server nears
expiration, the Client sends an RS over any underlay interface to
receive a fresh RA from the Hub. If no RA messages are received
over a first underlay interface (i.e., after retrying), the Client
marks the underlay interface as DOWN and should attempt to contact
the Hub Proxy/Server via a different underlay interface. If the
Hub Proxy/Server is unresponsive over additional underlay
interfaces, the Client sends an RS message with destination set to
the ADM-ULA of another Proxy/Server which will then assume the Hub
role.
* When all of a Client's underlay interfaces have transitioned to
DOWN (or if the prefix registration lifetime expires), the Hub
Proxy/Server withdraws the MNP the same as if it had received a
message with a release indication.
The Client is responsible for retrying each RS exchange up to
MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL
seconds until an RA is received. If no RA is received over an UP
underlay interface (i.e., even after attempting to contact alternate
Proxy/Servers), the Client declares this underlay interface as DOWN.
When changing to a new FHS or Hub Proxy/Server, the Client also
includes a Proxy/Server Departure OMNI sub-option in new RS messages;
the (new) FHS Proxy/Server will in turn send uNA messages to the old
FHS and/or Hub Proxy/Server to announce the Client's departure as
discussed in [I-D.templin-6man-aero].
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The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface.
Therefore, when the IPv6 layer sends an RS message the OMNI interface
returns an internally-generated RA message as though the message
originated from an IPv6 router. The internally-generated RA message
contains configuration information consistent with the information
received from the RAs generated by the Hub Proxy/Server. Whether the
OMNI interface IPv6 ND messaging process is initiated from the
receipt of an RS message from the IPv6 layer or independently of the
IPv6 layer is an implementation matter. Some implementations may
elect to defer the OMNI interface internal RS/RA messaging process
until an RS is received from the IPv6 layer, while others may elect
to initiate the process proactively. Still other deployments may
elect to administratively disable IPv6 layer RS/RA messaging over the
OMNI interface, since the messages are not required to drive the OMNI
interface internal RS/RA process. (Note that this same logic applies
to IPv4 implementations that employ "ICMP Router Discovery"
[RFC1256].)
Note: The Router Lifetime value in RA messages indicates the time
before which the Client must send another RS message over this
underlay interface (e.g., 600 seconds), however that timescale may be
significantly longer than the lifetime the MS has committed to retain
the prefix registration (e.g., REACHABLETIME seconds). Proxy/Servers
are therefore responsible for keeping MS state alive on a shorter
timescale than the Client may be required to do on its own behalf.
Note: On certain multicast-capable underlay interfaces, Clients
should send periodic unsolicited multicast NA messages and Proxy/
Servers should send periodic unsolicited multicast RA messages as
"beacons" that can be heard by other nodes on the link. If a node
fails to receive a beacon after a timeout value specific to the link,
it can initiate Neighbor Unreachability Detection (NUD) exchanges to
test reachability.
Note: If a single FHS Proxy/Server services multiple of a Client's
underlay interfaces, Window Synchronization will initially be
repeated for the RS/RA exchange over each underlay interface, i.e.,
until the Client discovers the many-to-one relationship. This will
naturally result in a single window synchronization that applies over
the Client's multiple underlay interfaces for the same FHS Proxy/
Server.
Note: Although the Client's FHS Proxy/Server is a first-hop segment
node from its own perspective, the Client stores the Proxy/Server's
FMT/SRT/ULA/INADDR as last-hop segment (LHS) information to supply to
neighbors. This allows both the Client and Hub Proxy/Server to
supply the information to neighbors that will perceive it as LHS
information on the return path to the Client.
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Note: The Hub Proxy/Server injects Client MNP-XLA into the routing
system by simply creating a route-to-interface forwarding table entry
for fd00::{MNP}/N via the OMNI interface. The dynamic routing
protocol will notice the new entry and advertise the route to its
peers. If the Hub receives additional RS messages, it need not re-
create the forwarding table entry (nor disturb the dynamic routing
protocol) if an entry is already present. If the Hub ceases to
receive RS messages from any of the Client's interfaces, it removes
the Client MNP-XLA from the forwarding table (i.e., after a short
delay) resulting in its removal also from the routing system.
Note: If the Client's initial RS message includes an anycast L2
destination address, the FHS Proxy/Server returns the solicited RA
using the same anycast address as the L2 source while including an
Interface Attributes sub-option with omIndex '0' and its true unicast
address in the INADDR. When the Client sends additional RS messages,
it includes this FHS Proxy/Server unicast address as the L2
destination and the FHS Proxy/Server returns the solicited RA using
the same unicast address as the L2 source. This will ensure that RS/
RA exchanges are not impeded by any NATs on the path while avoiding
long-term exposure of messages that use an anycast address as the
source.
Note: The Origin Indication sub-option is included only by the FHS
Proxy/Server and not by the Hub (unless the Hub is also serving as an
FHS).
Note: Clients should set the N/A/U flags consistently in successive
RS messages and only change those settings when an FHS/Hub Proxy/
Server service profile update is necessary.
Note: After a Client has discovered its MNP-ULAs for a given set of
FHS Proxy/Servers, it should begin using its MNP-XLA as the IPv6 ND
message source address and MNP-ULA as the OAL source address in
future IPv6 ND messages and refrain from further use of TMP-ULAs. In
any case, the Client SHOULD NOT gratuitously configure and use large
numbers of additional TMP-ULAs, as doing so would simply result in
address change churn in neighbor cache entries with no operational
advantages.
Note: Although the Client adds the Hub Proxy/Server ADM-ULA to the
default router list, it also caches the ADM-ULAs of the FHS Proxy/
Servers on the path to the Hub over each underlying interface. When
the Client needs to send a packet to a default router, it therefore
selects an ADM-ULA corresponding to the selected interface which
directs the packet to an FHS Proxy/Server for that interface. The
FHS Proxy/Server then forwards the packet without disturbing the Hub.
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15.1. Window Synchronization
In environments where Identification window synchronization is
necessary, the RS/RA exchanges discussed above observe the principles
specified in Section 6.6. Window synchronization is conducted
between the Client and each FHS Proxy/Server used to contact the Hub
Proxy/Server, i.e., and not between the Client and the Hub. This is
due to the fact that the Hub Proxy/Server is responsible only for
forwarding control and data messages via the secured spanning tree to
FHS Proxy/Servers, and is not responsible for forwarding messages
directly to the Client under a synchronized window. Also, in the
reverse direction the FHS Proxy/Servers handle all default forwarding
actions without forwarding Client-initiated data to the Hub.
When a Client needs to perform window synchronization via a new FHS
Proxy/Server, it sets the RS source address to its own MNP-XLA (or a
TMP-ULA) and destination address to the ADM-ULA of the Hub Proxy/
Server (or to All-Routers multicast in an initial RS), then sets the
SYN flag and includes an initial Sequence Number for Window
Synchronization. The Client then performs OAL encapsulation using
its own MNP-ULA (or a TMP-ULA) as the source and the ADM-ULA of the
FHS Proxy/Server as the destination and includes an Interface
Attributes sub-option then forwards the resulting carrier packets to
the FHS Proxy/Server. The FHS Proxy/Server then extracts the RS
message and caches the Window Synchronization parameters then re-
encapsulates with its own ADM-ULA as the source and the ADM-ULA of
the Hub Proxy/Server as the target.
The FHS Proxy/Server then forwards the resulting carrier packets via
the secured spanning tree to the Hub Proxy/Server, which updates the
Client's Interface Attributes and returns a unicast RA message with
source set to its own ADM-ULA and destination set to the RS source
address and with the Client's Interface Attributes echoed. The Hub
Proxy/Server then performs OAL encapsulation using its own ADM-ULA as
the source and the ADM-ULA of the FHS Proxy/Server as the
destination, then forwards the carrier packets via the secured
spanning tree to the FHS Proxy/Server. The FHS Proxy/Server then
proxys the message as discussed in the previous section and includes
responsive Window Synchronization information. The FHS Proxy/Server
then forwards the message to the Client which updates its window
synchronization information for the FHS Proxy/Server as necessary.
Following the initial RS/RA-driven window synchronization, the Client
can re-assert new windows with specific FHS Proxy/Servers by
performing NS/NA exchanges between its own MNP-XLAs and the ADM-ULAs
of the FHS Proxy/Servers without having to disturb the Hub.
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15.2. Router Discovery in IP Multihop and IPv4-Only Networks
On some *NETs, a Client may be located multiple IP hops away from the
nearest OMNI link Proxy/Server. Forwarding through IP multihop *NETs
is conducted through the application of a routing protocol (e.g., a
MANET/VANET routing protocol over omni-directional wireless
interfaces, an inter-domain routing protocol in an enterprise
network, etc.). Example routing protocols optimized for MANET/VANET
operations include [RFC3684] and [RFC5614] which operate according to
the link model articulated in [RFC5889] and subnet model articulated
in [RFC5942].
A Client located potentially multiple *NET hops away from the nearest
Proxy/Server prepares an RS message, sets the source address to its
MNP-XLA (or to a TMP-ULA if it does not yet have an MNP), and sets
the destination to link-scoped All-Routers multicast or a unicast
ADM-ULA the same as discussed above. The OMNI interface then employs
OAL encapsulation, sets the OAL source address to the TMP-ULA and
sets the OAL destination to an OMNI IPv6 anycast address based on
either a native IPv6 or IPv4-Compatible IPv6 prefix (see:
Section 10).
For IPv6-enabled *NETs, if the underlay interface does not configure
an IPv6 GUA the Client injects the TMP-ULA into the IPv6 multihop
routing system and forwards the message without further
encapsulation. Otherwise, the Client encapsulates the message in
UDP/IPv6 L2 headers, sets the source to the underlay interface IPv6
address and sets the destination to the same OMNI IPv6 anycast
address. The Client then forwards the message into the IPv6 multihop
routing system which conveys it to the nearest Proxy/Server that
advertises a matching OMNI IPv6 anycast prefix. If the nearest
Proxy/Server is too busy, it should forward (without Proxying) the
OAL-encapsulated RS to another nearby Proxy/Server connected to the
same IPv6 (multihop) network that also advertises the matching OMNI
IPv6 anycast prefix.
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For IPv4-only *NETs, the Client encapsulates the RS message in UDP/
IPv4 L2 headers, sets the source to the underlay interface IPv4
address and sets the destination to the OMNI IPv4 anycast address.
The Client then forwards the message into the IPv4 multihop routing
system which conveys it to the nearest Proxy/Server that advertises
the corresponding IPv4 prefix. If the nearest Proxy/Server is too
busy and/or does not configure the specified OMNI IPv6 anycast
address, it should forward (without Proxying) the OAL-encapsulated RS
to another nearby Proxy/Server connected to the same IPv4 (multihop)
network that configures the OMNI IPv6 anycast address. (In
environments where reciprocal RS forwarding cannot be supported, the
first Proxy/Server should instead return an RA based on its own
MSP(s).)
When an intermediate *NET hop that participates in the routing
protocol receives the encapsulated RS, it forwards the message
according to its routing tables (note that an intermediate node could
be a fixed infrastructure element such as a roadside unit or another
MANET/VANET node). This process repeats iteratively until the RS
message is received by a penultimate *NET hop within single-hop
communications range of a Proxy/Server, which forwards the message to
the Proxy/Server.
When a Proxy/Server that configures the OMNI IPv6 anycast OAL
destination receives the message, it decapsulates the RS and assumes
either the Hub or FHS role (in which case, it forwards the RS to a
candidate Hub). The Hub Proxy/Server then prepares an RA message
with source address set to its own ADM-ULA and destination address
set to the RS source address if it is acting only as the Hub (or to
the Client MNP-ULA within its ULA subnet prefix if it is also acting
as the FHS Proxy/Server). The Hub Proxy/Server then performs OAL
encapsulation with the RA OAL source/destination set to the RS OAL
destination/source and forwards the RA either to the FHS Proxy/Server
or directly to the Client.
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When the Hub or FHS Proxy/Server forwards the RA to the Client, it
encapsulates the message in L2 encapsulation headers (if necessary)
with (src, dst) set to the (dst, src) of the RS L2 encapsulation
headers. The Proxy/Server then forwards the message to a *NET node
within communications range, which forwards the message according to
its routing tables to an intermediate node. The multihop forwarding
process within the *NET continues repetitively until the message is
delivered to the original Client, which decapsulates the message and
performs autoconfiguration the same as if it had received the RA
directly from a Proxy/Server on the same physical link. The Client
then injects the MNP-ULA into the IPv6 multihop routing system if
necessary, then begins using the MNP-ULA as its OAL source address
and suspends use of its TMP-ULA since it now has a unique address
within the FHS Proxy/Server's "Multilink Subnet".
Note: When the RS message includes anycast OAL and/or L2
encapsulation destinations, the FHS Proxy/Server must use the same
anycast addresses as the OAL and/or L2 encapsulation sources to
support forwarding of the RA message and any initial data packets
over any NATs on the path. When the Client receives the RA, it will
discover its unicast MNP-ULA and/or L2 encapsulation addresses and
can forward future packets using the unicast (instead of anycast)
addresses to populate NAT state in the forward path. (If the Client
does not have immediate data to send to the FHS Proxy/Server, it can
instead send an OAL "bubble" - see Section 6.10.) After the Client
begins using unicast OAL/L2 encapsulation addresses in this way, the
FHS Proxy/Server should also begin using the same unicast addresses
in the reverse direction.
Note: When an OMNI interface configures a TMP-ULA, any nodes that
forward an encapsulated RS message with the ULA as the OAL source
must not consider the message as being specific to a particular OMNI
link. TMP-ULAs can therefore also serve as the source and
destination addresses of unencapsulated IPv6 data communications
within the local routing region, and if the TMP-ULAs are injected
into the local network routing protocol their prefix length must be
set to 128.
15.3. DHCPv6-based Prefix Registration
When a Client is not pre-provisioned with an MNP (or, when the Client
requires additional MNP delegations), it requests the MS to select
MNPs on its behalf and set up the correct routing state. The DHCPv6
service [RFC8415] supports this requirement.
When a Client requires the MS to select MNPs, it sends an RS message
with source set to a TMP-ULA. If the Client requires only a single
MNP delegation, it can then include a OMNI Node Identification sub-
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option plus an OMNI Neighbor Coordination sub-option with Preflen set
to the length of the desired MNP. If the Client requires multiple
MNP delegations and/or more complex DHCPv6 services, it instead
includes a DHCPv6 Message sub-option containing a Client Identifier,
one or more IA_PD options and a Rapid Commit option then sets the
'msg-type' field to "Solicit", and includes a 3 octet 'transaction-
id'. The Client then sets the RS destination to link-scoped All-
Routers multicast and sends the message using OAL encapsulation and
fragmentation if necessary as discussed above.
When the Hub Proxy/Server receives the RS message, it performs OAL
reassembly if necessary. Next, if the RS source is a TMP-ULA and/or
the OMNI option includes a DHCPv6 message sub-option, the Hub Proxy/
Server acts as a "Proxy DHCPv6 Client" in a message exchange with the
locally-resident DHCPv6 server. If the RS did not contain a DHCPv6
message sub-option, the Hub Proxy/Server generates a DHCPv6 Solicit
message on behalf of the Client using an IA_PD option with the prefix
length set to the OMNI Neighbor Coordination header Preflen value and
with a Client Identifier formed from the OMNI option Node
Identification sub-option; otherwise, the Hub Proxy/Server uses the
DHCPv6 Solicit message contained in the OMNI option. The Hub Proxy/
Server then sends the DHCPv6 message to the DHCPv6 Server, which
delegates MNPs and returns a DHCPv6 Reply message with PD parameters.
(If the Hub Proxy/Server wishes to defer creation of Client state
until the DHCPv6 Reply is received, it can instead act as a
Lightweight DHCPv6 Relay Agent per [RFC6221] by encapsulating the
DHCPv6 message in a Relay-forward/reply exchange with Relay Message
and Interface ID options. In the process, the Hub Proxy/Server packs
any state information needed to return an RA to the Client in the
Relay-forward Interface ID option so that the information will be
echoed back in the Relay-reply.)
When the Hub Proxy/Server receives the DHCPv6 Reply, it creates MNP-
XLAs based on the delegated MNPs and creates OMNI interface MNP-XLA
forwarding table entries (i.e., to prompt the dynamic routing
protocol). The Hub Proxy/Server then sends an RA back to the FHS
Proxy/Server with the DHCPv6 Reply message included in an OMNI DHCPv6
message sub-option. The Hub Proxy/Server sets the RA destination
address to the RS source address, sets the RA source address to its
own ADM-ULA, performs OAL encapsulation and fragmentation, performs
L2 encapsulation and sends the RA to the Client via the FHS Proxy/
Server as discussed above.
When the FHS Proxy/Server receives the RA, it changes the RA
destination address to the MNP-ULA for the Client within its own ULA
subnet prefix then forwards the RA to the Client. When the Client
receives the RA, it reassembles and discards the OAL encapsulation
then creates a default route, assigns Subnet Router Anycast addresses
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and uses the RA destination address or DHCPv6-delegated MNP to
automatically configure its primary MNP-ULA. The Client will then
use these primary MNP-based addresses as the source address of any
IPv6 ND messages it sends as long as it retains ownership of the MNP.
Note: when the Hub Proxy/Server is also the FHS Proxy/Server, it
forwards the RA message directly to the Client with the destination
set to the Client's MNP-ULA (i.e., instead of forwarding via another
Proxy/Server).
15.4. OMNI Link Extension
Clients can provide an OMNI link ingress point for other nodes on
their (downstream) ENETs that also act as Clients. When Client A has
already coordinated with an (upstream) ANET/INET Proxy/Server, Client
B on an ENET serviced by Client A can send OAL-encapsulated RS
messages with addresses set the same as specified in Section 15.2.
When Client A receives the RS message, it infers from the OAL
encapsulation that Client B is seeking to establish itself as a
Client instead of just a simple ENET Host.
Client A then returns an RA message the same as a Proxy/Server would
do as specified in Section 15.2 except that it instead uses its own
MNP-ULA as the RA and OAL source addresses and performs (recursive)
DHCPv6 Prefix Delegation. The MNP delegation in the RA message must
be a sub-MNP from the MNP delegated to Client A. For example, if
Client A receives the MNP 2001:db8:1000::/48 it can provide a sub-
delegation such as 2001:db8:1000:2000::/56 to Client B. Client B can
in turn sub-delegate 2001:db8:1000:2000::/56 to its own ENET(s),
where there may be a further prospective Client C that would in turn
request OMNI link services via Client B.
To support this Client-to-Client chaining, Clients send IPv6 ND
messages addressed to the OMNI link anycast address via their ANET/
INET (i.e., upstream) interfaces, but advertise the OMNI link anycast
address into their ENET (i.e., downstream) networks where there may
be further prospective Clients wishing to join the chain. The ENET
of the upstream Client is therefore seen as an ANET by downstream
Clients, and the upstream Client is seen as a Proxy/Server by
downstream Clients.
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16. Secure Redirection
If the underlay network link model is multiple access, the FHS Proxy/
Server is responsible for assuring that address duplication cannot
corrupt the neighbor caches of other nodes on the link. When the
Client sends an RS message on a multiple access underlay network, the
Proxy/Server verifies that the Client is authorized to use the
address and responds with an RA (or forwards the RS to the Hub) only
if the Client is authorized.
After verifying Client authorization and returning an RA, the Proxy/
Server MAY return IPv6 ND Redirect messages to direct Clients located
on the same underlay network to exchange packets directly without
transiting the Proxy/Server. In that case, the Clients can exchange
packets according to their unicast L2 addresses discovered from the
Redirect message instead of using the dogleg path through the Proxy/
Server. In some underlay networks, however, such direct
communications may be undesirable and continued use of the dogleg
path through the Proxy/Server may provide better performance. In
that case, the Proxy/Server can refrain from sending Redirects, and/
or Clients can ignore them.
17. Proxy/Server Resilience
*NETs SHOULD deploy Proxy/Servers in Virtual Router Redundancy
Protocol (VRRP) [RFC5798] configurations so that service continuity
is maintained even if one or more Proxy/Servers fail. Using VRRP,
the Client is unaware which of the (redundant) FHS Proxy/Servers is
currently providing service, and any service discontinuity will be
limited to the failover time supported by VRRP. Widely deployed
public domain implementations of VRRP are available.
Proxy/Servers SHOULD use high availability clustering services so
that multiple redundant systems can provide coordinated response to
failures. As with VRRP, widely deployed public domain
implementations of high availability clustering services are
available. Note that special-purpose and expensive dedicated
hardware is not necessary, and public domain implementations can be
used even between lightweight virtual machines in cloud deployments.
18. Detecting and Responding to Proxy/Server Failures
In environments where fast recovery from Proxy/Server failure is
required, FHS Proxy/Servers SHOULD use proactive Neighbor
Unreachability Detection (NUD) in a manner that parallels
Bidirectional Forwarding Detection (BFD) [RFC5880] to track Hub
Proxy/Server reachability. FHS Proxy/Servers can then quickly detect
and react to failures so that cached information is re-established
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through alternate paths. Proactive NUD control messaging is carried
only over well-connected ground domain networks (i.e., and not low-
end links such as aeronautical radios) and can therefore be tuned for
rapid response.
FHS Proxy/Servers perform proactive NUD for Hub Proxy/Servers for
which there are currently active Clients. If a Hub Proxy/Server
fails, the FHS Proxy/Server can quickly inform Clients of the outage
by sending multicast RA messages. The FHS Proxy/Server sends RA
messages to Clients with source set to the ADM-ULA of the Hub, with
destination address set to All-Nodes multicast (ff02::1) [RFC4291]
and with Router Lifetime set to 0.
The FHS Proxy/Server SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA
messages separated by small delays [RFC4861]. Any Clients that have
been using the (now defunct) Hub Proxy/Server will receive the RA
messages.
19. Transition Considerations
When a Client connects to an *NET link for the first time, it sends
an RS message with an OMNI option. If the first hop router
recognizes the option, it responds according to the appropriate FHS/
Hub Proxy/Server role resulting in an RA message with an OMNI option
returned to the Client. The Client then engages this FHS Proxy/Sever
according to the OMNI link model specified above. If the first hop
router is a legacy IPv6 router, however, it instead returns an RA
message with no OMNI option and with a non-OMNI unicast source LLA as
specified in [RFC4861]. In that case, the Client engages the *NET
according to the legacy IPv6 link model and without the OMNI
extensions specified in this document.
If the *NET link model is multiple access, there must be assurance
that address duplication cannot corrupt the neighbor caches of other
nodes on the link. When the Client sends an RS message on a multiple
access *NET link with an OMNI option, first hop routers that
recognize the option ensure that the Client is authorized to use the
address and return an RA with a non-zero Router Lifetime only if the
Client is authorized. First hop routers that do not recognize the
OMNI option instead return an RA that makes no statement about the
Client's authorization to use the source address. In that case, the
Client should perform Duplicate Address Detection to ensure that it
does not interfere with other nodes on the link.
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An alternative approach for multiple access *NET links to ensure
isolation for Client-Proxy/Server communications is through link-
layer address mappings as discussed in Appendix D. This arrangement
imparts a (virtual) point-to-point link model over the (physical)
multiple access link.
20. OMNI Interfaces on Open Internetworks
Client OMNI interfaces configured over IPv6-enabled underlay
interfaces on an open Internetwork without an OMNI-aware first-hop
router receive IPv6 RA messages with no OMNI options, while OMNI
interfaces configured over IPv4-only underlay interfaces receive no
IPv6 RA messages at all (but may receive IPv4 RA messages [RFC1256]).
Client OMNI interfaces that receive RA messages with OMNI options
configure addresses, on-link prefixes, etc. on the underlay interface
that received the RA according to standard IPv6 ND and address
resolution conventions [RFC4861] [RFC4862]. Client OMNI interfaces
configured over IPv4-only underlay interfaces configure IPv4 address
information on the underlay interfaces using mechanisms such as
DHCPv4 [RFC2131].
Client OMNI interfaces configured over underlay interfaces connected
to open Internetworks can apply security services such as VPNs to
connect to a Proxy/Server, or can establish a direct link to the
Proxy/Server through some other means (see Section 4). In
environments where an explicit VPN or direct link may be impractical
or undesirable, Client OMNI interfaces can instead send IPv6 ND
messages with OMNI options that include authentication signatures.
OMNI interfaces use UDP/IP as L2 encapsulation headers for
transmission over open Internetworks with UDP service port number
8060 (see: Section 25.13 and Section 3.6 of [I-D.templin-6man-aero])
for both IPv4 and IPv6 underlay interfaces. The OMNI interface
submits original IP packets for OAL encapsulation, then encapsulates
the resulting OAL fragments in UDP/IP L2 headers to form carrier
packets. (The first four bits following the UDP header determine
whether the OAL headers are uncompressed/compressed as discussed in
Section 6.4.) The OMNI interface sets the UDP length to the
encapsulated OAL fragment length and sets the IP length to an
appropriate value at least as large as the UDP datagram.
For Client-Proxy/Server (e.g., "Vehicle-to-Infrastructure (V2I)")
neighbor exchanges, the source must include an OMNI option with an
authentication sub-option in all IPv6 ND messages. The source can
apply HIP security services per [RFC7401] using the IPv6 ND message
OMNI option as a "shipping container" to convey an authentication
signature in a (unidirectional) HIP "Notify" message. For Client-
Client (e.g., "Vehicle-to-Vehicle (V2V)") neighbor exchanges, two
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Clients can exchange HIP "Initiator/Responder" messages coded in OMNI
options of multiple IPv6 NS/NA messages for mutual authentication
according to the HIP protocol. (Note: a simple Hashed Message
Authentication Code (HMAC) such as specified in [RFC4380] or the
QUIC-TLS connection-oriented service [RFC9000] can be used as an
alternate authentication service in some environments.)
When an OMNI interface includes an authentication sub-option, it must
appear as the first sub-option of the first OMNI option in the IPv6
ND message which must appear immediately following the IPv6 ND
message header. When an OMNI interface prepares a HIP message sub-
option, it includes its own (H)HIT as the Sender's HIT and the
neighbor's (H)HIT if known as the Receiver's HIT (otherwise 0). If
(H)HITs are not available within the OMNI operational environment,
the source can instead include other IPv6 address types instead of
(H)HITs as long as the Sender and Receiver have some way to associate
information embedded in the IPv6 address with the neighbor; such
information could include a node identifier, vehicle identifier, MAC
address, etc.
Before calculating the authentication signature, the source includes
any other necessary sub-options (such as Interface Attributes and
Origin Indication) and sets both the IPv6 ND message Checksum and
authentication signature fields to 0. The source then calculates the
authentication signature over the full length of the IPv6 ND message
beginning with a pseudo-header of the IPv6 header (i.e., the same as
specified in [RFC4443]) and extending over the length of the message.
(If the IPv6 ND message is part of an OAL super-packet, the source
instead calculates the authentication signature over the remainder of
the super-packet.) The source next writes the authentication
signature into the sub-option signature field and forwards the
message.
After establishing a VPN or preparing for UDP/IP encapsulation, OMNI
interfaces send RS/RA messages for Client-Proxy/Server coordination
(see: Section 15) and NS/NA messages for route optimization, window
synchronization and mobility management (see:
[I-D.templin-6man-aero]). These control plane messages must be
authenticated while other control and data plane messages are
delivered the same as for ordinary best-effort traffic with source
address and/or Identification window-based data origin verification.
Upper layer protocol sessions over OMNI interfaces that connect over
open Internetworks without an explicit VPN should therefore employ
transport- or higher-layer security to ensure authentication,
integrity and/or confidentiality.
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Clients should avoid using INET Proxy/Servers as general-purpose
routers for steady streams of carrier packets that do not require
authentication. Clients should instead perform route optimization to
coordinate with other INET nodes that can provide forwarding services
(or preferably coordinate directly with peer Clients directly)
instead of burdening the Proxy/Server. Procedures for coordinating
with peer Clients and discovering INET nodes that can provide better
forwarding services are discussed in [I-D.templin-6man-aero].
Clients that attempt to contact peers over INET underlay interfaces
often encounter NATs in the path. OMNI interfaces accommodate NAT
traversal using UDP/IP encapsulation and the mechanisms discussed in
[I-D.templin-6man-aero]. FHS Proxy/Servers include Origin
Indications in RA messages to allow Clients to detect the presence of
NATs.
Note: Following the initial IPv6 ND message exchange, OMNI interfaces
configured over INET underlay interfaces maintain neighbor
relationships by transmitting periodic IPv6 ND messages with OMNI
options that include HIP "Update" and/or "Notify" messages. When
HMAC authentication is used instead of HIP, the Client and Proxy/
Server exchange all IPv6 ND messages with HMAC signatures included
based on a shared-secret. When QUIC-TLS connections are used, the
Client and Proxy/Server observe QUIC-TLS conventions
[RFC9000][RFC9001].
Note: OMNI interfaces configured over INET underlay interfaces should
employ the Identification window synchronization mechanisms specified
in Section 6.6 in order to exclude spurious carrier packets that
might otherwise clutter the reassembly cache. This is especially
important in environments where carrier packet spoofing and/or
corruption is a threat.
Note: NATs may be present on the path from a Client to its FHS Proxy/
Server, but never on the path from the FHS Proxy/Server to the Hub
where only INET and/or spanning tree hops occur. Therefore, the FHS
Proxy/Server does not communicate Client origin information to the
Hub where it would serve no purpose.
21. Time-Varying MNPs
In some use cases, it is desirable, beneficial and efficient for the
Client to receive a constant MNP that travels with the Client
wherever it moves. For example, this would allow air traffic
controllers to easily track aircraft, etc. In other cases, however
(e.g., intelligent transportation systems), the Client may be willing
to sacrifice a modicum of efficiency in order to have time-varying
MNPs that can be changed every so often to defeat adversarial
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tracking.
The prefix delegation services discussed in Section 15.3 allows
Clients that desire time-varying MNPs to obtain short-lived prefixes
to send RS messages with a TMP-ULA source address and/or with an OMNI
option with DHCPv6 Option sub-options. The Client would then be
obligated to renumber its internal networks whenever its MNP (and
therefore also its OMNI address) changes. This should not present a
challenge for Clients with automated network renumbering services,
but may disrupt persistent sessions that would prefer to use a
constant address.
22. (H)HITs and Temporary ULA (TMP-ULA)s
Clients that generate (H)HITs but do not have pre-assigned MNPs can
request MNP delegations by issuing IPv6 ND messages that use the
(H)HIT instead of a TMP-ULA. For example, when a Client creates an
RS message it can set the source to a (H)HIT and destination to link-
scoped All-Routers multicast. The IPv6 ND message includes an OMNI
option with a HIP message sub-option, and need not include a Node
Identification sub-option if the Client's (H)HIT appears in the HIP
message. The Client then encapsulates the message in an IPv6 header
with the (H)HIT as the source address. The Client then sends the
message as specified in Section 15.2.
When the Hub Proxy/Server receives the RS message, it notes that the
source was a (H)HIT, then invokes the DHCPv6 protocol to request an
MNP prefix delegation while using the (H)HIT (in the form of a DUID)
as the Client Identifier. The Hub Proxy/Server then prepares an RA
message with source address set to its own ADM-ULA and destination
set to the source of the RS message. The Hub Proxy/Server next
includes an OMNI option with a HIP message sub-option and any DHCPv6
prefix delegation parameters. The Proxy/Server finally encapsulates
the RA in an OAL header with source address set to its own ADM-ULA
and destination set to the RS OAL source address, then returns the
encapsulated RA to the Client either directly or by way of the FHS
Proxy/Server as a proxy.
Clients can also use (H)HITs and/or TMP-ULAs for direct Client-to-
Client communications outside the context of any OMNI link supporting
infrastructure. When two Clients encounter one another they can use
their (H)HITs and/or TMP-ULAs as original IPv6 packet source and
destination addresses to support direct communications. Clients can
also inject their (H)HITs and/or TMP-ULAs into an IPv6 multihop
routing protocol to enable multihop communications as discussed in
Section 15.2. Clients can further exchange other IPv6 ND messages
using their (H)HITs and/or TMP-ULAs as source and destination
addresses.
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Lastly, when Clients are within the coverage range of OMNI link
infrastructure a case could be made for injecting (H)HITs and/or TMP-
ULAs into the global MS routing system. For example, when the Client
sends an RS to an FHS Proxy/Server it could include a request to
inject the (H)HIT / TMP-ULA into the routing system instead of
requesting an MNP prefix delegation. This would potentially enable
OMNI link-wide communications using only (H)HITs or TMP-ULAs, and not
MNPs. This document notes the opportunity, but makes no
recommendation.
23. Address Selection
Clients assign LLAs to the OMNI interface, but do not use LLAs as
IPv6 ND message source/destination addresses nor for addressing
ordinary original IP packets exchanged with OMNI link neighbors.
Clients use MNP-ULAs as source/destination IPv6 addresses in the
encapsulation headers of OAL packets and use MNP-XLAs as the IPv6
source addresses of the IPv6 ND messages themselves. Clients use
TMP-ULAs when an MNP is not available, or as source/destination IPv6
addresses for communications within a MANET/VANET local area.
Clients can also use (H)HITs instead of ULAs for local communications
when operation outside the context of a specific ULA domain and/or
source address attestation is necessary.
Clients use MNP-based GUAs as original IP packet source and
destination addresses for communications with Internet destinations
when they are within range of OMNI link supporting infrastructure
that can inject the MNP into the routing system. Clients can also
use MNP-based GUAs within multihop routing regions that are currently
disconnected from infrastructure as long as the corresponding MNP-
ULAs have been injected into the routing system.
Clients use anycast GUAs as OAL and/or L2 encapsulation destination
addresses for RS messages used to discover the nearest FHS Proxy/
Server. When the Proxy/Server returns a solicited RA, it must also
use the same anycast address as the RA OAL/L2 encapsulation source in
order to successfully traverse any NATs in the path. The Client
should then immediately transition to using the FHS Proxy/Server's
discovered unicast OAL/L2 address as the destination in order to
minimize dependence on the Proxy/Server's use of an anycast source
address.
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24. Error Messages
An OAL destination or intermediate node may need to return
ICMPv6-like error messages (e.g., Destination Unreachable, Packet Too
Big, Time Exceeded, etc.) [RFC4443] to an OAL source. Since ICMPv6
error messages do not themselves include authentication codes, OAL
nodes can return error messages as an OMNI ICMPv6 Error sub-option in
a secured IPv6 ND uNA message.
25. IANA Considerations
The following IANA actions are requested in accordance with [RFC8126]
and [RFC8726]:
25.1. "Protocol Numbers" Registry
The IANA is instructed to allocate an Internet Protocol number TBD1
from the 'protocol numbers' registry for the Overlay Multilink
Network Interface (OMNI) protocol. Guidance is found in [RFC5237]
(registration procedure is IESG Approval or Standards Action).
25.2. "IEEE 802 Numbers" Registry
During final publication stages, the IESG will be requested to
procure an IEEE EtherType value TBD2 for OMNI according to the
statement found at https://www.ietf.org/about/groups/iesg/statements/
ethertypes/.
Following this procurement, the IANA is instructed to register the
value TBD2 in the 'ieee-802-numbers' registry for Overlay Multilink
Network Interface (OMNI) encapsulation on Ethernet networks.
Guidance is found in [RFC7042] (registration procedure is Expert
Review).
25.3. "IPv4 Special-Purpose Address" Registry
The IANA is instructed to assign TBD3/N as an "OMNI IPv4 anycast"
address/prefix in the "IPv4 Special-Purpose Address" registry in a
similar fashion as for [RFC3068]. The IANA is requested to work with
the authors to obtain a TBD3/N public IPv4 prefix, whether through an
RIR allocation, a delegation from IANA's "IPv4 Recovered Address
Space" registry or through an unspecified third party donation.
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25.4. "IPv6 Neighbor Discovery Option Formats" Registry
The IANA is instructed to allocate an official Type number TBD4 from
the "IPv6 Neighbor Discovery Option Formats" registry for the OMNI
option (registration procedure is RFC required). Implementations set
Type to 253 as an interim value [RFC4727].
25.5. "Ethernet Numbers" Registry
The IANA is instructed to allocate one Ethernet unicast address TBD5
(suggested value '00-52-14') in the 'ethernet-numbers' registry under
"IANA Unicast 48-bit MAC Addresses" (registration procedure is Expert
Review). The registration should appear as follows:
Addresses Usage Reference
--------- ----- ---------
00-52-14 Overlay Multilink Network (OMNI) Interface [RFCXXXX]
Figure 35: IANA Unicast 48-bit MAC Addresses
25.6. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry
The IANA is instructed to assign two new Code values in the "ICMPv6
Code Fields: Type 2 - Packet Too Big" registry (registration
procedure is Standards Action or IESG Approval). The registry should
appear as follows:
Code Name Reference
--- ---- ---------
0 PTB Hard Error [RFC4443]
1 PTB Soft Error (loss) [RFCXXXX]
2 PTB Soft Error (no loss) [RFCXXXX]
Figure 36: ICMPv6 Code Fields: Type 2 - Packet Too Big Values
(Note: this registry also to be used to define values for setting the
"unused" field of ICMPv4 "Destination Unreachable - Fragmentation
Needed" messages.)
25.7. "OMNI Option Sub-Type Values" (New Registry)
The OMNI option defines a 5-bit Sub-Type field, for which IANA is
instructed to create and maintain a new registry entitled "OMNI
Option Sub-Type Values". Initial values are given below
(registration procedure is RFC required):
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Value Sub-Type name Reference
----- ------------- ----------
0 Pad1 [RFCXXXX]
1 PadN [RFCXXXX]
2 Neighbor Coordination [RFCXXXX]
3 Interface Attributes [RFCXXXX]
4 Multilink Forwarding Params [RFCXXXX]
5 Traffic Selector [RFCXXXX]
6 Geo Coordinates [RFCXXXX]
7 DHCPv6 Message [RFCXXXX]
8 HIP Message [RFCXXXX]
9 PIM-SM Message [RFCXXXX]
10 Fragmentation Report [RFCXXXX]
11 Node Identification [RFCXXXX]
12 ICMPv6 Error [RFCXXXX]
13 QUIC-TLS Message [RFCXXXX]
14 Proxy/Server Departure [RFCXXXX]
15-29 Unassigned
30 Sub-Type Extension [RFCXXXX]
31 Reserved by IANA [RFCXXXX]
Figure 37: OMNI Option Sub-Type Values
25.8. "OMNI Geo Coordinates Type Values" (New Registry)
The OMNI Geo Coordinates sub-option (see: Section 12.2.7) contains an
8-bit Type field, for which IANA is instructed to create and maintain
a new registry entitled "OMNI Geo Coordinates Type Values". Initial
values are given below (registration procedure is RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 NULL [RFCXXXX]
1-252 Unassigned [RFCXXXX]
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 38: OMNI Geo Coordinates Type
25.9. "OMNI Node Identification ID-Type Values" (New Registry)
The OMNI Node Identification sub-option (see: Section 12.2.12)
contains an 8-bit ID-Type field, for which IANA is instructed to
create and maintain a new registry entitled "OMNI Node Identification
ID-Type Values". Initial values are given below (registration
procedure is RFC required):
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Value Sub-Type name Reference
----- ------------- ----------
0 UUID [RFCXXXX]
1 HIT [RFCXXXX]
2 HHIT [RFCXXXX]
3 Network Access Identifier [RFCXXXX]
4 FQDN [RFCXXXX]
5 IPv6 Address [RFCXXXX]
6-252 Unassigned [RFCXXXX]
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 39: OMNI Node Identification ID-Type Values
25.10. "OMNI Option Sub-Type Extension Values" (New Registry)
The OMNI option defines an 8-bit Extension-Type field for Sub-Type 30
(Sub-Type Extension), for which IANA is instructed to create and
maintain a new registry entitled "OMNI Option Sub-Type Extension
Values". Initial values are given below (registration procedure is
RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 RFC4380 UDP/IP Header Option [RFCXXXX]
1 RFC6081 UDP/IP Trailer Option [RFCXXXX]
2-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 40: OMNI Option Sub-Type Extension Values
25.11. "OMNI RFC4380 UDP/IP Header Option" (New Registry)
The OMNI Sub-Type Extension "RFC4380 UDP/IP Header Option" defines an
8-bit Header Type field, for which IANA is instructed to create and
maintain a new registry entitled "OMNI RFC4380 UDP/IP Header Option".
Initial registry values are given below (registration procedure is
RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 Origin Indication (IPv4) [RFC4380]
1 Authentication Encapsulation [RFC4380]
2 Origin Indication (IPv6) [RFCXXXX]
3-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
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Figure 41: OMNI RFC4380 UDP/IP Header Option
25.12. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry)
The OMNI Sub-Type Extension for "RFC6081 UDP/IP Trailer Option"
defines an 8-bit Trailer Type field, for which IANA is instructed to
create and maintain a new registry entitled "OMNI RFC6081 UDP/IP
Trailer Option". Initial registry values are given below
(registration procedure is RFC required):
Value Sub-Type name Reference
----- ------------- ----------
0 Unassigned
1 Nonce [RFC6081]
2 Unassigned
3 Alternate Address (IPv4) [RFC6081]
4 Neighbor Discovery Option [RFC6081]
5 Random Port [RFC6081]
6 Alternate Address (IPv6) [RFCXXXX]
7-252 Unassigned
253-254 Reserved for Experimentation [RFCXXXX]
255 Reserved by IANA [RFCXXXX]
Figure 42: OMNI RFC6081 Trailer Option
25.13. Additional Considerations
The IANA has assigned the UDP port number "8060" for an earlier
experimental version of AERO [RFC6706]. This document reclaims the
UDP port number "8060" for 'aero' as the service port for UDP/IP
encapsulation. (Note that, although [RFC6706] is not widely
implemented or deployed, any messages coded to that specification can
be easily distinguished and ignored since they include an invalid
ICMPv6 message type number '0'.) The IANA is therefore instructed to
update the reference for UDP port number "8060" from "RFC6706" to
"RFCXXXX" (i.e., this document) while retaining the existing name
'aero'.
The IANA has assigned a 4 octet Private Enterprise Number (PEN) code
"45282" in the "enterprise-numbers" registry. This document is the
normative reference for using this code in DHCP Unique IDentifiers
based on Enterprise Numbers ("DUID-EN for OMNI Interfaces") (see:
Section 11). The IANA is therefore instructed to change the
enterprise designation for PEN code "45282" from "LinkUp Networks" to
"Overlay Multilink Network Interface (OMNI)".
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The IANA has assigned the ifType code "301 - omni - Overlay Multilink
Network Interface (OMNI)" in accordance with Section 6 of [RFC8892].
The registration appears under the IANA "Structure of Management
Information (SMI) Numbers (MIB Module Registrations) - Interface
Types (ifType)" registry.
No further IANA actions are required.
26. Security Considerations
Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6
Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages
SHOULD include Nonce and Timestamp options [RFC3971] when transaction
confirmation and/or time synchronization is needed. (Note however
that when OAL encapsulation is used the (echoed) OAL Identification
value can provide sufficient transaction confirmation.)
OMNI interfaces configured over secured ANET/ENET interfaces inherit
the physical and/or link-layer security properties (i.e., "protected
spectrum") of the connected networks. OMNI interfaces configured
over open INET interfaces can use symmetric securing services such as
VPNs or can by some other means establish a direct link. When a VPN
or direct link may be impractical or undesirable, however, the
security services specified in [RFC7401], [RFC4380] or [RFC9000] can
be employed. While the OMNI link protects control plane messaging,
applications must still employ end-to-end transport- or higher-layer
security services to protect the data plane.
Strong network layer security for control plane messages and
forwarding path integrity for data plane messages between Proxy/
Servers MUST be supported. In one example, the AERO service
[I-D.templin-6man-aero] constructs an SRT spanning tree with Proxy/
Serves as leaf nodes and secures the spanning tree links with network
layer security mechanisms such as IPsec [RFC4301] or WireGuard [WG].
Secured control plane messages are then constrained to travel only
over the secured spanning tree paths and are therefore protected from
attack or eavesdropping. Other control and data plane messages can
travel over route optimized paths that do not strictly follow the
secured spanning tree, therefore end-to-end sessions should employ
transport- or higher-layer security services. Additionally, the OAL
Identification value can provide a first level of data origin
authentication to mitigate off-path spoofing in some environments.
Identity-based key verification infrastructure services such as iPSK
may be necessary for verifying the identities claimed by Clients.
This requirement should be harmonized with the manner in which
(H)HITs are attested in a given operational environment.
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Security considerations for specific access network interface types
are covered under the corresponding IP-over-(foo) specification
(e.g., [RFC2464], [RFC2492], etc.).
Security considerations for IPv6 fragmentation and reassembly are
discussed in Section 6.12. In environments where spoofing is
considered a threat, OMNI nodes SHOULD employ Identification window
synchronization and OAL destinations SHOULD configure an (end-system-
based) firewall.
27. Implementation Status
AERO/OMNI Release-3.2 was tagged on March 30, 2021, and is undergoing
internal testing. Additional internal releases expected within the
coming months, with first public release expected end of 1H2021.
Many AERO/OMNI functions are implemented and undergoing final
integration. OAL fragmentation/reassembly buffer management code has
been cleared for public release.
28. Document Updates
This document does not itself update other RFCs, but suggests that
the following could be updated through future IETF initiatives:
* [RFC1191]
* [RFC2675]
* [RFC4291]
* [RFC4443]
* [RFC8201]
Updates can be through, e.g., standards action, the errata process,
etc. as appropriate.
29. Acknowledgements
The first version of this document was prepared per the consensus
decision at the 7th Conference of the International Civil Aviation
Organization (ICAO) Working Group-I Mobility Subgroup on March 22,
2019. Consensus to take the document forward to the IETF was reached
at the 9th Conference of the Mobility Subgroup on November 22, 2019.
Attendees and contributors included: Guray Acar, Danny Bharj,
Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo,
Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu
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Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg
Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane
Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman,
Fryderyk Wrobel and Dongsong Zeng.
The following individuals are acknowledged for their useful comments:
Amanda Baber, Stuart Card, Donald Eastlake, Adrian Farrel, Michael
Matyas, Robert Moskowitz, Madhu Niraula, Greg Saccone, Stephane
Tamalet, Eliot Lear, Eduard Vasilenko, Eric Vyncke. Pavel Drasil,
Zdenek Jaron and Michal Skorepa are especially recognized for their
many helpful ideas and suggestions. Akash Agarwal, Madhuri Madhava
Badgandi, Sean Dickson, Don Dillenburg, Joe Dudkowski, Vijayasarathy
Rajagopalan, Ron Sackman, Bhargava Raman Sai Prakash and Katherine
Tran are acknowledged for their hard work on the implementation and
technical insights that led to improvements for the spec.
Discussions on the IETF 6man and atn mailing lists during the fall of
2020 suggested additional points to consider. The authors gratefully
acknowledge the list members who contributed valuable insights
through those discussions. Eric Vyncke and Erik Kline were the
intarea ADs, while Bob Hinden and Ole Troan were the 6man WG chairs
at the time the document was developed; they are all gratefully
acknowledged for their many helpful insights. Many of the ideas in
this document have further built on IETF experiences beginning in the
1990s, with insights from colleagues including Ron Bonica, Brian
Carpenter, Ralph Droms, Christian Huitema, Thomas Narten, Dave
Thaler, Joe Touch, Pascal Thubert, and many others who deserve
recognition.
Early observations on IP fragmentation performance implications were
noted in the 1986 Digital Equipment Corporation (DEC) "qe reset"
investigation, where fragment bursts from NFS UDP traffic triggered
hardware resets resulting in communication failures. Jeff Chase,
Fred Glover and Chet Juzsczak of the Ultrix Engineering Group led the
investigation, and determined that setting a smaller NFS mount block
size reduced the amount of fragmentation and suppressed the resets.
Early observations on L2 media MTU issues were noted in the 1988 DEC
FDDI investigation, where Raj Jain, KK Ramakrishnan and Kathy Wilde
represented architectural considerations for FDDI networking in
general including FDDI/Ethernet bridging. Jeff Mogul (who led the
IETF Path MTU Discovery working group) and other DEC colleagues who
supported these early investigations are also acknowledged.
Throughout the 1990's and into the 2000's, many colleagues supported
and encouraged continuation of the work. Beginning with the DEC
Project Sequoia effort at the University of California, Berkeley,
then moving to the DEC research lab offices in Palo Alto CA, then to
Sterling Software at the NASA Ames Research Center, then to SRI in
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Menlo Park, CA, then to Nokia in Mountain View, CA and finally to the
Boeing Company in 2005 the work saw continuous advancement through
the encouragement of many. Those who offered their support and
encouragement are gratefully acknowledged.
This work is aligned with the NASA Safe Autonomous Systems Operation
(SASO) program under NASA contract number NNA16BD84C.
This work is aligned with the FAA as per the SE2025 contract number
DTFAWA-15-D-00030.
This work is aligned with the Boeing Information Technology (BIT)
Mobility Vision Lab (MVL) program.
30. References
30.1. Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <https://www.rfc-editor.org/info/rfc4191>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
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[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4,
ICMPv6, UDP, and TCP Headers", RFC 4727,
DOI 10.17487/RFC4727, November 2006,
<https://www.rfc-editor.org/info/rfc4727>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont,
"Traffic Selectors for Flow Bindings", RFC 6088,
DOI 10.17487/RFC6088, January 2011,
<https://www.rfc-editor.org/info/rfc6088>.
[RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by
Hosts in a Multi-Prefix Network", RFC 8028,
DOI 10.17487/RFC8028, November 2016,
<https://www.rfc-editor.org/info/rfc8028>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>.
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[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
30.2. Informative References
[ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground
Interface for Civil Aviation, IETF Liaison Statement
#1676, https://datatracker.ietf.org/liaison/1676/", 3
March 2020.
[ATN-IPS] WG-I, ICAO., "ICAO Document 9896 (Manual on the
Aeronautical Telecommunication Network (ATN) using
Internet Protocol Suite (IPS) Standards and Protocol),
Draft Edition 3 (work-in-progress)", 10 December 2020.
[CKSUM] Stone, J., Greenwald, M., Partridge, C., and J. Hughes,
"Performance of Checksums and CRC's Over Real Data, IEEE/
ACM Transactions on Networking, Vol. 6, No. 5", October
1998.
[CRC] Jain, R., "Error Characteristics of Fiber Distributed Data
Interface (FDDI), IEEE Transactions on Communications",
August 1990.
[I-D.ietf-drip-rid]
Moskowitz, R., Card, S. W., Wiethuechter, A., and A.
Gurtov, "DRIP Entity Tag (DET) for Unmanned Aircraft
System Remote ID (UAS RID)", Work in Progress, Internet-
Draft, draft-ietf-drip-rid-22, 13 April 2022,
<https://www.ietf.org/archive/id/draft-ietf-drip-rid-
22.txt>.
[I-D.ietf-intarea-tunnels]
Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", Work in Progress, Internet-Draft, draft-
ietf-intarea-tunnels-10, 12 September 2019,
<https://www.ietf.org/archive/id/draft-ietf-intarea-
tunnels-10.txt>.
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[I-D.ietf-ipwave-vehicular-networking]
Jeong, J. (., "IPv6 Wireless Access in Vehicular
Environments (IPWAVE): Problem Statement and Use Cases",
Work in Progress, Internet-Draft, draft-ietf-ipwave-
vehicular-networking-28, 30 March 2022,
<https://www.ietf.org/archive/id/draft-ietf-ipwave-
vehicular-networking-28.txt>.
[I-D.templin-6man-aero]
Templin, F. L., "Automatic Extended Route Optimization
(AERO)", Work in Progress, Internet-Draft, draft-templin-
6man-aero-42, 9 April 2022,
<https://www.ietf.org/archive/id/draft-templin-6man-aero-
42.txt>.
[I-D.templin-6man-fragrep]
Templin, F. L., "IPv6 Fragment Retransmission and Path MTU
Discovery Soft Errors", Work in Progress, Internet-Draft,
draft-templin-6man-fragrep-07, 29 March 2022,
<https://www.ietf.org/archive/id/draft-templin-6man-
fragrep-07.txt>.
[I-D.templin-6man-lla-type]
Templin, F. L., "The IPv6 Link-Local Address Type Field",
Work in Progress, Internet-Draft, draft-templin-6man-lla-
type-02, 23 November 2020,
<https://www.ietf.org/archive/id/draft-templin-6man-lla-
type-02.txt>.
[I-D.templin-intarea-parcels]
Templin, F. L., "IP Parcels", Work in Progress, Internet-
Draft, draft-templin-intarea-parcels-10, 29 March 2022,
<https://www.ietf.org/archive/id/draft-templin-intarea-
parcels-10.txt>.
[IPV4-GUA] Postel, J., "IPv4 Address Space Registry,
https://www.iana.org/assignments/ipv4-address-space/ipv4-
address-space.xhtml", 14 December 2020.
[IPV6-GUA] Postel, J., "IPv6 Global Unicast Address Assignments,
https://www.iana.org/assignments/ipv6-unicast-address-
assignments/ipv6-unicast-address-assignments.xhtml", 14
December 2020.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
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[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC1146] Zweig, J. and C. Partridge, "TCP alternate checksum
options", RFC 1146, DOI 10.17487/RFC1146, March 1990,
<https://www.rfc-editor.org/info/rfc1146>.
[RFC1149] Waitzman, D., "Standard for the transmission of IP
datagrams on avian carriers", RFC 1149,
DOI 10.17487/RFC1149, April 1990,
<https://www.rfc-editor.org/info/rfc1149>.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/info/rfc1191>.
[RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages",
RFC 1256, DOI 10.17487/RFC1256, September 1991,
<https://www.rfc-editor.org/info/rfc1256>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
<https://www.rfc-editor.org/info/rfc2464>.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
December 1998, <https://www.rfc-editor.org/info/rfc2473>.
[RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM
Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999,
<https://www.rfc-editor.org/info/rfc2492>.
[RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
RFC 2675, DOI 10.17487/RFC2675, August 1999,
<https://www.rfc-editor.org/info/rfc2675>.
[RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group
MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000,
<https://www.rfc-editor.org/info/rfc2863>.
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[RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery",
RFC 2923, DOI 10.17487/RFC2923, September 2000,
<https://www.rfc-editor.org/info/rfc2923>.
[RFC2983] Black, D., "Differentiated Services and Tunnels",
RFC 2983, DOI 10.17487/RFC2983, October 2000,
<https://www.rfc-editor.org/info/rfc2983>.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, DOI 10.17487/RFC3056, February
2001, <https://www.rfc-editor.org/info/rfc3056>.
[RFC3068] Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
RFC 3068, DOI 10.17487/RFC3068, June 2001,
<https://www.rfc-editor.org/info/rfc3068>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330,
DOI 10.17487/RFC3330, September 2002,
<https://www.rfc-editor.org/info/rfc3330>.
[RFC3366] Fairhurst, G. and L. Wood, "Advice to link designers on
link Automatic Repeat reQuest (ARQ)", BCP 62, RFC 3366,
DOI 10.17487/RFC3366, August 2002,
<https://www.rfc-editor.org/info/rfc3366>.
[RFC3684] Ogier, R., Templin, F., and M. Lewis, "Topology
Dissemination Based on Reverse-Path Forwarding (TBRPF)",
RFC 3684, DOI 10.17487/RFC3684, February 2004,
<https://www.rfc-editor.org/info/rfc3684>.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692,
DOI 10.17487/RFC3692, January 2004,
<https://www.rfc-editor.org/info/rfc3692>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
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[RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, DOI 10.17487/RFC3819, July 2004,
<https://www.rfc-editor.org/info/rfc3819>.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/info/rfc4122>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
DOI 10.17487/RFC4380, February 2006,
<https://www.rfc-editor.org/info/rfc4380>.
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
2006, <https://www.rfc-editor.org/info/rfc4389>.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
<https://www.rfc-editor.org/info/rfc4429>.
[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605,
August 2006, <https://www.rfc-editor.org/info/rfc4605>.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
<https://www.rfc-editor.org/info/rfc4821>.
[RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly
Errors at High Data Rates", RFC 4963,
DOI 10.17487/RFC4963, July 2007,
<https://www.rfc-editor.org/info/rfc4963>.
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[RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
Chowdhury, K., and B. Patil, "Proxy Mobile IPv6",
RFC 5213, DOI 10.17487/RFC5213, August 2008,
<https://www.rfc-editor.org/info/rfc5213>.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
DOI 10.17487/RFC5214, March 2008,
<https://www.rfc-editor.org/info/rfc5214>.
[RFC5237] Arkko, J. and S. Bradner, "IANA Allocation Guidelines for
the Protocol Field", BCP 37, RFC 5237,
DOI 10.17487/RFC5237, February 2008,
<https://www.rfc-editor.org/info/rfc5237>.
[RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)",
RFC 5558, DOI 10.17487/RFC5558, February 2010,
<https://www.rfc-editor.org/info/rfc5558>.
[RFC5614] Ogier, R. and P. Spagnolo, "Mobile Ad Hoc Network (MANET)
Extension of OSPF Using Connected Dominating Set (CDS)
Flooding", RFC 5614, DOI 10.17487/RFC5614, August 2009,
<https://www.rfc-editor.org/info/rfc5614>.
[RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
Version 3 for IPv4 and IPv6", RFC 5798,
DOI 10.17487/RFC5798, March 2010,
<https://www.rfc-editor.org/info/rfc5798>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC5889] Baccelli, E., Ed. and M. Townsley, Ed., "IP Addressing
Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889,
September 2010, <https://www.rfc-editor.org/info/rfc5889>.
[RFC5942] Singh, H., Beebee, W., and E. Nordmark, "IPv6 Subnet
Model: The Relationship between Links and Subnet
Prefixes", RFC 5942, DOI 10.17487/RFC5942, July 2010,
<https://www.rfc-editor.org/info/rfc5942>.
[RFC6081] Thaler, D., "Teredo Extensions", RFC 6081,
DOI 10.17487/RFC6081, January 2011,
<https://www.rfc-editor.org/info/rfc6081>.
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[RFC6214] Carpenter, B. and R. Hinden, "Adaptation of RFC 1149 for
IPv6", RFC 6214, DOI 10.17487/RFC6214, April 2011,
<https://www.rfc-editor.org/info/rfc6214>.
[RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A.
Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221,
DOI 10.17487/RFC6221, May 2011,
<https://www.rfc-editor.org/info/rfc6221>.
[RFC6247] Eggert, L., "Moving the Undeployed TCP Extensions RFC
1072, RFC 1106, RFC 1110, RFC 1145, RFC 1146, RFC 1379,
RFC 1644, and RFC 1693 to Historic Status", RFC 6247,
DOI 10.17487/RFC6247, May 2011,
<https://www.rfc-editor.org/info/rfc6247>.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>.
[RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for
Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May
2012, <https://www.rfc-editor.org/info/rfc6543>.
[RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization
(AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012,
<https://www.rfc-editor.org/info/rfc6706>.
[RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
UDP Checksums for Tunneled Packets", RFC 6935,
DOI 10.17487/RFC6935, April 2013,
<https://www.rfc-editor.org/info/rfc6935>.
[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, DOI 10.17487/RFC6936, April 2013,
<https://www.rfc-editor.org/info/rfc6936>.
[RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation
with IPv6 Neighbor Discovery", RFC 6980,
DOI 10.17487/RFC6980, August 2013,
<https://www.rfc-editor.org/info/rfc6980>.
[RFC7042] Eastlake 3rd, D. and J. Abley, "IANA Considerations and
IETF Protocol and Documentation Usage for IEEE 802
Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042,
October 2013, <https://www.rfc-editor.org/info/rfc7042>.
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[RFC7094] McPherson, D., Oran, D., Thaler, D., and E. Osterweil,
"Architectural Considerations of IP Anycast", RFC 7094,
DOI 10.17487/RFC7094, January 2014,
<https://www.rfc-editor.org/info/rfc7094>.
[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<https://www.rfc-editor.org/info/rfc7401>.
[RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S.,
Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit
Boundary in IPv6 Addressing", RFC 7421,
DOI 10.17487/RFC7421, January 2015,
<https://www.rfc-editor.org/info/rfc7421>.
[RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542,
DOI 10.17487/RFC7542, May 2015,
<https://www.rfc-editor.org/info/rfc7542>.
[RFC7739] Gont, F., "Security Implications of Predictable Fragment
Identification Values", RFC 7739, DOI 10.17487/RFC7739,
February 2016, <https://www.rfc-editor.org/info/rfc7739>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface
Support for IP Hosts with Multi-Access Support", RFC 7847,
DOI 10.17487/RFC7847, May 2016,
<https://www.rfc-editor.org/info/rfc7847>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
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[RFC8726] Farrel, A., "How Requests for IANA Action Will Be Handled
on the Independent Stream", RFC 8726,
DOI 10.17487/RFC8726, November 2020,
<https://www.rfc-editor.org/info/rfc8726>.
[RFC8892] Thaler, D. and D. Romascanu, "Guidelines and Registration
Procedures for Interface Types and Tunnel Types",
RFC 8892, DOI 10.17487/RFC8892, August 2020,
<https://www.rfc-editor.org/info/rfc8892>.
[RFC8899] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T.
Völker, "Packetization Layer Path MTU Discovery for
Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
September 2020, <https://www.rfc-editor.org/info/rfc8899>.
[RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
and F. Gont, "IP Fragmentation Considered Fragile",
BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,
<https://www.rfc-editor.org/info/rfc8900>.
[RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves,
"Temporary Address Extensions for Stateless Address
Autoconfiguration in IPv6", RFC 8981,
DOI 10.17487/RFC8981, February 2021,
<https://www.rfc-editor.org/info/rfc8981>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[RFC9001] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
<https://www.rfc-editor.org/info/rfc9001>.
[RFC9002] Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
and Congestion Control", RFC 9002, DOI 10.17487/RFC9002,
May 2021, <https://www.rfc-editor.org/info/rfc9002>.
[WG] WireGuard, W., "WireGuard, Fast, Modern, Secure VPN
Tunnel, https://wireguard.com/", 7 March 2022.
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Appendix A. OAL Checksum Algorithm
The OAL Checksum Algorithm adopts the 8-bit Fletcher algorithm
specified in Appendix I of [RFC1146] as also analyzed in [CKSUM].
[RFC6247] declared [RFC1146] historic for the reason that the
algorithms had never seen widespread use with TCP, however this
document adopts the 8-bit Fletcher algorithm for a different purpose.
Quoting from Appendix I of [RFC1146], the OAL Checksum Algorithm
proceeds as follows:
"The 8-bit Fletcher Checksum Algorithm is calculated over a
sequence of data octets (call them D[1] through D[N]) by
maintaining 2 unsigned 1's-complement 8-bit accumulators A and B
whose contents are initially zero, and performing the following
loop where i ranges from 1 to N:
A := A + D[i]
B := B + A
It can be shown that at the end of the loop A will contain the
8-bit 1's complement sum of all octets in the datagram, and that B
will contain (N)D[1] + (N-1)D[2] + ... + D[N]."
To calculate the OAL checksum, the above algorithm is applied over
the N-octet concatenation of the OAL pseudo-header and the
encapsulated IP packet or packets. Specifically, the algorithm is
first applied over the 40 octets of the OAL pseudo-header as data
octets D[1] through D[40], then continues over the entire length of
the original IP packet(s) as data octets D[41] through D[N].
Appendix B. IPv6 ND Message Authentication and Integrity
OMNI interface IPv6 ND messages are subject to authentication and
integrity checks at multiple levels. When an OMNI interface sends an
IPv6 ND message over an INET interface, it includes an authentication
sub-option with a valid signature but does not include an IPv6 ND
message checksum. The OMNI interface that receives the message
verifies the OAL checksum as a first-level integrity check, then
verifies the authentication signature (while ignoring the IPv6 ND
message checksum) to ensure IPv6 ND message authentication and
integrity.
When an OMNI interface sends an IPv6 ND message over an underlay
interface connected to a secured network, it omits the authentication
sub-option but instead calculates/includes an IPv6 ND message
checksum. The OMNI interface that receives the message applies any
lower-layer authentication and integrity checks, then verifies both
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the OAL checksum and the IPv6 ND message checksum. (Note that
optimized implementations can verify both the OAL and IPv6 ND message
checksums in a single pass over the data.) When an OMNI interface
sends IPv6 ND messages to a synchronized neighbor, it includes an
authentication sub-option only if authentication is necessary;
otherwise, it calculates/includes the IPv6 ND message checksum.
When the OMNI interface calculates the authentication signature or
IPv6 ND message checksum, it performs the calculation beginning with
a pseudo-header of the IPv6 ND message header and extends over all
following OAL packet data. In particular, for OAL super-packets any
additional original IP packets included beyond the end of the IPv6 ND
message are simply considered as extensions of the IPv6 ND message
for the purpose of the calculation.
OAL destinations discard carrier packets with unacceptable
Identifications and submit the encapsulated fragments in all others
for reassembly. The reassembly algorithm rejects any fragments with
unacceptable sizes, offsets, etc. and reassembles all others.
Following reassembly, the OAL checksum algorithm provides an
integrity assurance layer that compliments any integrity checks
already applied by lower layers as well as a first-pass filter for
any checks that will be applied later by upper layers.
Appendix C. VDL Mode 2 Considerations
ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2"
(VDLM2) that specifies an essential radio frequency data link service
for aircraft and ground stations in worldwide civil aviation air
traffic management. The VDLM2 link type is "multicast capable"
[RFC4861], but with considerable differences from common multicast
links such as Ethernet and IEEE 802.11.
First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of
magnitude less than most modern wireless networking gear. Second,
due to the low available link bandwidth only VDLM2 ground stations
(i.e., and not aircraft) are permitted to send broadcasts, and even
so only as compact layer 2 "beacons". Third, aircraft employ the
services of ground stations by performing unicast RS/RA exchanges
upon receipt of beacons instead of listening for multicast RA
messages and/or sending multicast RS messages.
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This beacon-oriented unicast RS/RA approach is necessary to conserve
the already-scarce available link bandwidth. Moreover, since the
numbers of beaconing ground stations operating within a given spatial
range must be kept as sparse as possible, it would not be feasible to
have different classes of ground stations within the same region
observing different protocols. It is therefore highly desirable that
all ground stations observe a common language of RS/RA as specified
in this document.
Note that links of this nature may benefit from compression
techniques that reduce the bandwidth necessary for conveying the same
amount of data. The IETF lpwan working group is considering possible
alternatives: [https://datatracker.ietf.org/wg/lpwan/documents].
Appendix D. Client-Proxy/Server Isolation Through Link-Layer Address
Mapping
Per [RFC4861], IPv6 ND messages may be sent to either a multicast or
unicast link-scoped IPv6 destination address. However, IPv6 ND
messaging should be coordinated between the Client and Proxy/Server
only without invoking other nodes on the underlay network. This
implies that Client-Proxy/Server control messaging should be isolated
and not overheard by other nodes on the link.
To support Client-Proxy/Server isolation on some links, Proxy/Servers
can maintain an OMNI-specific unicast link-layer address ("MSADDR").
For Ethernet-compatible links, this specification reserves one
Ethernet unicast address TBD5 (see: IANA Considerations). For non-
Ethernet statically-addressed links MSADDR is reserved per the
assigned numbers authority for the link-layer addressing space. For
still other links, MSADDR may be dynamically discovered through other
means, e.g., link-layer beacons.
Clients map the L3 addresses of all IPv6 ND messages they send (i.e.,
both multicast and unicast) to MSADDR instead of to an ordinary
unicast or multicast link-layer address. In this way, all of the
Client's IPv6 ND messages will be received by Proxy/Servers that are
configured to accept packets destined to MSADDR. Note that multiple
Proxy/Servers on the link could be configured to accept packets
destined to MSADDR, e.g., as a basis for supporting redundancy.
Therefore, Proxy/Servers must accept and process packets destined to
MSADDR, while all other devices must not process packets destined to
MSADDR. This model has well-established operational experience in
Proxy Mobile IPv6 (PMIP) [RFC5213][RFC6543].
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Appendix E. Change Log
<< RFC Editor - remove prior to publication >>
Differences from earlier versions:
* Submit for RFC publication.
Author's Address
Fred L. Templin (editor)
The Boeing Company
P.O. Box 3707
Seattle, WA 98124
United States of America
Email: fltemplin@acm.org
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