Network Working Group Dimitri Papadimitriou
Internet Draft (Alcatel)
Category: Standard
Expiration Date: February 2007 October 2006
OSPFv2 Routing Protocols Extensions for ASON Routing
draft-ietf-ccamp-gmpls-ason-routing-ospf-02.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
The Generalized MPLS (GMPLS) suite of protocols has been defined to
control different switching technologies as well as different
applications. These include support for requesting TDM connections
including SONET/SDH and Optical Transport Networks (OTNs).
This document provides the extensions of the OSPFv2 Link State
Routing Protocol to meet the routing requirements for an
Automatically Switched Optical Network (ASON) as defined by ITU-T.
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1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
The reader is assumed to be familiar with the terminology and
requirements developed in [RFC4258] and the evaluation outcomes
detailed in [ASON-EVAL].
2. Introduction
There are certain capabilities that are needed to support the ITU-T
Automatically Switched Optical Network (ASON) control plane
architecture as defined in [G.8080]. [RFC4258] details the routing
requirements for the GMPLS suite of routing protocols to support the
capabilities and functionality of ASON control planes identified in
[G.7715] and in [G.7715.1].
Section 7 of [ASON-EVAL] evaluates the IETF Link State Routing
Protocols against the requirements identified in [RFC4258]. Section
7.1 of [ASON-EVAL] summarizes the capabilities to be provided by
OSPFv2 [RFC2328] in support of ASON routing. From the candidate
routing protocols identified in [ASON-EVAL] (OSPFv2 and IS-IS), this
document details the OSPFv2 specifics for ASON routing.
ASON (Routing) terminology sections are provided in Appendix 1 and 2.
3. Reachability
In order to advertise blocks of reachable address prefixes a
summarization mechanism is introduced that complements the
techniques described in [OSPF-NODE].
This extension takes the form of a network mask (a 32-bit number
indicating the range of IP addresses residing on a single IP
network/subnet). The set of local addresses are carried in an OSPFv2
TE LSA node attribute TLV (a specific sub-TLV is defined per address
family, e.g., IPv4 and IPv6).
The proposed solution is to advertise the local address prefixes of
a router as new sub-TLVs of the (OSPFv2 TE LSA) Node Attribute top
level TLV (of Type TBD). This document defines the following sub-
TLVs:
- Node IPv4 Local Prefix sub-TLV: Type 3 - Length: variable
- Node IPv6 Local Prefix sub-TLV: Type 4 - Length: variable
3.1 Node IPv4 local prefix sub-TLV
The node IPv4 local prefix sub-TLV has a type of 3 and contains one
or more local IPv4 prefixes. It has the following format:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 3 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . .
. . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The length is set to 8 * n where n is the number of local prefixes
included in the sub-TLV.
Network mask: A 32-bit number indicating the IPv4 address mask
for the advertised destination prefix.
Each <Network mask, IPv4 Address> pair listed as part of this sub-
TLV represents a reachable destination prefix hosted by the
advertising Router ID.
The local addresses that can be learned from TE LSAs i.e. router
address and TE interface addresses SHOULD not be advertised in the
node IPv4 local prefix sub-TLV.
3.2 Node IPv6 local prefix sub-TLV
The node IPv6 local prefix sub-TLV has a type of 4 and contains one
or more local IPv6 prefixes. IPv6 Prefix Representation uses RFC
2740 Section A.4.1. It has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PrefixLength | PrefixOptions | (0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Address Prefix 1 |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . .
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. . .
. . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PrefixLength | PrefixOptions | (0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Address Prefix n |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PrefixLength: length in bits of the prefix.
PrefixOptions: 8-bit field describing various capabilities
associated with the prefix (see [RFC2740] Section A.4.2).
Address Prefix: encoding of the prefix itself as an even multiple of
32-bit words, padding with zero bits as necessary.
The Length is set to Sum[n][4 + #32-bit words/4] where n is the
number of local prefixes included in the sub-TLV.
The local addresses that can be learned from TE LSAs i.e. router
address and TE interface addresses SHOULD not be advertised in the
node IPv6 local prefix sub-TLV.
4. Link Attribute
4.1 Local Adaptation
The Local Adaptation is defined as TE link attribute (i.e. sub-TLV)
that describes the cross/inter-layer relationships.
The Interface Switching Capability Descriptor (ISCD) TE Attribute
[RFC4202] identifies the ability of the TE link to support cross-
connection to another link within the same layer and the ability to
use a locally terminated connection that belongs to one layer as a
data link for another layer (adaptation capability). However, the
information associated to the ability to terminate connections
within that layer (referred to as the termination capability) is
embedded with the adaptation capability.
For instance, a link between two optical cross-connects will contain
at least one ISCD attribute describing LSC switching capability.
Whereas a link between an optical cross-connect and an IP/MPLS LSR
will contain at least two ISCD attributes: one for the description
of the LSC termination capability and one for the PSC adaptation
capability.
Note that per [RFC4202], an interface may have more than one ISCD
sub-TLV. Hence, the corresponding advertisements should not result
in any compatibility issue.
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In OSPFv2, the Interface Switching Capability Descriptor is a sub-
TLV (of type 15) of the top-level Link TLV (of type 2) [RFC4203].
The adaptation and termination capabilities are advertised using two
separate ISCD sub-TLVs within the same top-level link TLV.
4.2 Technology Specific Bandwidth Accounting
GMPLS Routing defines an Interface Switching Capability Descriptor
(ISCD) that delivers among others the information about the
(maximum/minimum) bandwidth per priority an LSP can make use of.
In the ASON context, accounting on per timeslot basis using 32-bit
tuples of the form <signal_type (8 bits); number of unallocated
timeslots (24 bits)> may optionally be incorporated in the
technology specific field of the ISCD TE link attribute when the
switching capability field is set to TDM value. When included,
format and encoding MUST follow the rules defined in [RFC4202].
The purpose is purely informative: there is no mandatory processing
or topology/traffic-engineering significance associated to this
information.
In OSPFv2, the Interface Switching Capability Descriptor is a sub-
TLV (of type 15) of the Link TLV (of type 2).
5. Routing Information Scope
5.1. Terminology and Identification
o) Pi is a physical (bearer/data/transport plane) node.
o) Li is a logical control plane entity that is associated to a
single data plane (abstract) node. Each Li is identified by a unique
TE Router_ID. The latter is a control plane identifier, defined as
the Router_Address top level TLV of the Type 1 TE LSA [RFC3630].
Note: the Router_Address top-level TLV definition, processing and
usage remain per [RFC 3630]. This TLV specifies a stable IP address
of the advertising router that is always reachable if there is any
IP connectivity to it. Each advertising router, therefore,
advertises a unique, reachable IP address for each Pi on behalf of
which it makes advertisements.
o) Ri is a logical control plane entity that is associated to a
control plane "router". The latter is the source for topology
information that it generates and shares with other control plane
"routers". The Ri is identified by the (advertising) Router_ID (32-
bit) [RFC2328].
The Router_ID, which is represented by Ri and which corresponds to
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the RC_ID [RFC4258], does not enter into the identification of the
logical entities representing the data plane resources such as
links. The Routing DataBase (RDB) is associated to the Ri.
Aside from the Li/Pi mappings, these identifiers are not assumed to
be in a particular entity relationship except that the Ri may have
multiple Lis in its scope. The relationship between Ri and Li is
simple at any moment in time: an Li may be advertised by only one Ri
at any time. However, an Ri may advertise a set of one or more Lis.
Hence, the OSPFv2 routing protocol must support a single Ri
advertising on behalf of more than one Li.
5.2 Link Advertisement (Local and Remote TE Router ID sub-TLV)
A Router_ID (Ri) advertising on behalf multiple TE Router_IDs (Lis)
creates a 1:N relationship between the Router_ID and the TE
Router_ID. As the link local and link remote (unnumbered) ID
association is not unique per node (per Li unicity), the
advertisement needs to indicate the remote Lj value and rely on the
initial discovery process to retrieve the [Li;Lj] relationship. In
brief, as unnumbered links have their ID defined on per Li bases,
the remote Lj needs to be identified to scope the link remote ID to
the local Li. Therefore, the routing protocol MUST be able to
disambiguate the advertised TE links so that they can be associated
with the correct TE Router ID.
For this purpose, a new sub-TLV of the (OSPFv2 TE LSA) top level
Link TLV is introduced that defines the local and the remote
TE_Router_ID.
The type of this sub-TLV is 17, and length is eight octets. The
value field of this sub-TLV contains four octets of Local TE Router
Identifier followed by four octets of Remote TE Router Identifier.
The value of the Local and the Remote TE Router Identifier SHOULD
NOT be set to 0.
The format of this sub-TLV is the following:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 17 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local TE Router Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote TE Router Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This sub-TLV is optional and SHOULD only be included as part of the
top level Link TLV if the Router_ID is advertising on behalf of more
than one TE_Router_ID. In any other case, this sub-TLV SHOULD be
omitted except if operator plans to start of with 1 Li and
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progressively add more Li's (under the same Ri) such as to maintain
consistency.
Note: The Link ID sub-TLV that identifies the other end of the link
(i.e. Router ID of the neighbor for point-to-point links) MUST
appear exactly once per Link TLV. This sub-TLV MUST be processed as
defined in [RFC3630].
5.3 Reachability Advertisement (Local TE Router ID sub-TLV)
When the Router_ID advertises on behalf of multiple TE Router_IDs
(Lis), the routing protocol MUST be able to associate the advertised
reachability information with the correct TE Router ID.
For this purpose, a new sub-TLV of the (OSPFv2 TE LSA) top level
Node Attribute TLV is introduced. This TLV associates the local
prefixes (sub-TLV 3 and 4, see above) to a given TE Router_ID.
The type of this sub-TLV is 5, and length is four octets. The value
field of this sub-TLV contains four octets of Local TE Router
Identifier [RFC3630].
The format of this sub-TLV is the following:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local TE Router Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This sub-TLV is optional and SHOULD only be included as part of the
Node Attribute TLV if the Router_ID is advertising on behalf of more
than one TE_Router_ID. In any other case, this sub-TLV SHOULD be
omitted.
6. Routing Information Dissemination
An ASON RA represents a partition of the data plane and its
identifier is used within the control plane as the representation of
this partition. A RA may contain smaller RAs inter-connected by
links. The limit of the subdivision results in a RA that contains two
sub-networks interconnected by a single link. ASON RA levels do not
reflect routing protocol levels (such as OSPF areas). OSPF routing
areas containing routing areas that recursively define successive
hierarchical levels of RAs can be represented by separate instances
of the protocol.
RCs supporting RAs disseminate downward/upward this hierarchy. The
vertical routing information dissemination mechanisms described in
this section do not introduce or imply a new OSPF routing area
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hierarchy. RCs supporting RAs at multiple levels are structured as
separate OSPF instances with routing information exchanges between
levels described by import/export rules.
The implication is that an RC that performs import/export of routing
information as described in this document does not implement an Area
Border Router (ABR) functionality.
6.1 Import/Export Rules
RCs supporting RAs disseminate downward/upward the hierarchy by
importing/exporting this routing information as Opaque TE LSA
(Opaque Type 1) of LS Type 10. The information that MAY be exchanged
between adjacent levels includes the Router_Address, Link and
Node_Attribute top level TLV.
The Opaque TE LSA import/export rules are governed as follows:
- If the export target interface is associated to the same area as
the one associated with the import interface, the Opaque LSA MUST
NOT imported.
- If a match is found between the Advertising Router ID in the
header of the received Opaque TE LSA and one of the Router ID
belonging to the area of the export target interface, the Opaque
LSA MUST NOT be imported.
- If these two conditions are not met the Opaque TE LSA MAY be
imported and MAY be disseminated following the OSPF flooding
rules.
The imported/exported content MAY be transformed e.g. filtered, as
long as the resulting routing information is consistent. In
particular, when more than one RC are bound to adjacent levels and
both are allowed to import/export routing information it is expected
that these transformation are performed in consistent manner.
Definition of these policy mechanisms is outside the scope of this
document.
In practice, and in order to avoid scalability and processing
overhead, routing information imported/exported downward/upward the
hierarchy is expected to include reachability information (see
Section 3) and upon strict policy control link topology information.
6.2 Discovery and Selection
6.2.1 Upward Discovery and Selection
In order to discover RCs that are capable to disseminate routing
information upward the routing hierarchy, the following Capability
Descriptor bit [OSPF-CAP] are defined:
- U bit: when set, this flag indicates that the RC is capable to
disseminate routing information upward the adjacent level.
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In case of multiple RC are advertized with their U bit set, the RC
with the highest Router ID, among the RCs having set the U bit,
SHOULD be selected as the RC for upward dissemination of routing
information. The other RCs MUST NOT participate in the upward
dissemination of routing information as long as the opaque LSA
information corresponding to the highest Router ID RC does not reach
MaxAge. This mechanism prevents from having more than one RC
advertizing routing information upward the routing hierarchy.
Note that alternatively if this information cannot be discovered
automatically, it MUST be manually configured.
Once an RC has been selected, it remains unmodified even if an RC
with a highest Router ID is introduced and advertizes its capability
to disseminate routing information upward the adjacent level (i.e.
U-bit set). This hysteresis mechanism prevents from disturbing the
upward routing information dissemination process in case e.g. of
flapping.
6.2.2 Downward Discovery and Selection
The same discovery mechanism is used for selecting the RC taking in
charge dissemination of routing information downward the hierarchy.
However, an additional restriction MUST be applied such that the RC
selection process takes into account that an upper level may be
adjacent to one or more lower (routing area) levels. For this
purpose a specific TLV indexing the (lower) area ID to which the
RC's are capable to disseminate routing information is needed.
OSPF Downstream Associated Area ID TLV format carried in the OSPF
router information LSA [OSPF-CAP] is defined. This TLV has the
following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Associated Area ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// ... //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Associated Area ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (16 bits): identifies the TLV type
Length (16 bits): length of the value field in octets
Value (n x 32 bits): Associated Area ID whose value space is the
Area ID as defined in [RFC2328].
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Note that this information MUST be present when the D bit is set. To
discover RCs that are capable to disseminate routing information
downward the routing hierarchy, the following Capability Descriptor
bit [OSPF-CAP] is defined, that MUST be advertised together with the
OSPF Downstream Associated Area ID TLV:
- D bit: when set, this flag indicates that the RC is capable to
disseminate routing information downward the adjacent level(s).
In case of multiple supporting RCs for the same Associated Area ID,
the RC with the highest Router ID, among the RCs having set the D
bit, MUST be selected as the RC for downward dissemination of
routing information. The other RCs for the same Associated Area ID
MUST not participate in the downward dissemination of routing
information as long as the opaque LSA information corresponding to
the highest Router ID RC does not reach MaxAge. This mechanism
prevents from having more than one RC advertizing routing
information downward the routing hierarchy.
Note that alternatively if this information cannot be discovered
automatically, it MUST be manually configured.
The OSPF Router information opaque LSA (opaque type of 4, opaque ID
of 0) and its content in particular, the Router Informational
Capabilities TLV [OSPF-CAP] and TE Node Capability Descriptor TLV
[OSPF-TE-CAP] MUST NOT be re-originated.
6.3 Loop prevention
When more than one RC are bound to adjacent levels of the hierarchy,
configured and selected to redistribute upward and downward the
routing information, a specific mechanism is required to avoid
looping/re-introduction of routing information back to the upper
level. This specific case occurs e.g. when the RC advertizing
routing information downward the hierarchy is not the one
advertizing routing upward the hierarchy (or vice-versa).
When these conditions are met, it is necessary to have a mean by
which an RC receiving an Opaque TE LSA imported/exported downward by
an RC associated to the same area, omits to import/export back the
content of this LSA upward into the (same) upper level.
Note that configuration and operational simplification can be
obtained when both functionality are configured on a single RC (per
pair of adjacent level) fulfilling both roles. Figure 1 provides an
example where such simplification applies.
....................................................
. .
. RC_5 ------------ RC_6 .
. | | .
. | | Area Y .
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. ********* ********* .
............* RC_1a *.........* RC_2a *.............
__________* | * * | *
............* RC_1b *... ...* RC 2b *.............
. ********* . . ********* .
. | . . | .
. Area Z | . . | Area X .
. RC_3 . . RC_4 .
. . . .
........................ .........................
Figure 1. Hierarchical Environment (Example)
In this case, the procedure described in this section MAY be
omitted, as long as these conditions are permanently guaranteed. In
all other cases, without exception, the procedure described in this
section MUST be applied.
6.3.1 Associated Area ID
Thus, we need some way of filtering the downward/upward re-
originated Opaque TE LSA. Per [RFC2370], the information contained
in Opaque LSAs may be used directly by OSPF. Henceforth, by adding
the Area ID associated to the incoming routing information the loop
prevention problem can be solved. This additional information that
MAY be carried in opaque LSAs including the Router Address TLV, in
opaque LSAs including the Link TLV, and in opaque LSAs including the
Node Attribute TLV, is referred to as the Associated Area ID.
The format of the Associated Area ID TLV is defined as follows:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Associated Area ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (16 bits): identifies the TLV type
Length (16 bits): length of the value field in octets
Value (32 bits): Associated Area ID whose value space is the Area ID
as defined in [RFC2328].
6.3.2 Processing
When fulfilling the rules detailed in Section 6.1 a given Opaque LSA
is imported/exported downward or upward the routing hierarchy, the
Associated Area ID TLV is added to the received opaque LSA list of
TLVs such as to identify the area from where this routing
information has been received.
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When the RC adjacent to the lower or upper level routing level
receives this opaque LSA, the following rule is applied (in addition
the rule governing the import/export of opaque LSAs as detailed in
Section 6.1).
- If a match is found between the Associated Area ID of the received
Opaque TE LSA and the Area ID belonging to the area of the export
target interface, the Opaque LSA MUST NOT be imported.
- Otherwise, this opaque LSA MAY be imported and disseminated
downward or upward the routing hierarchy following the OSPF
flooding rules.
This mechanism ensures that no race condition occurs when the
conditions depicted in Figure 2 are met.
RC_5 ------------- RC_6
| |
| | Area Y
********* *********
..........* RC_1a *.........* RC_2a *............
__________* | * * | *
..........* RC_1b *.........* RC 2b *............
********* *********
| |
| | Area X
RC_3 --- . . . --- RC_4
Figure 2. Race Condition Prevention (Example)
Assume that RC_1b is configured for exporting routing information
upward toward Area Y (upward the routing hierarchy) and that RC_2a
is configured for exporting routing information toward Area X
(downward the routing hierarchy).
Assumes that routing information advertised by RC_3 would reach
faster to RC_4 across Area Y through hierarchy.
If RC_2b is not able to prevent from importing that information,
RC_4 may receive that information before the same advertisement
would propagate in Area X (from RC 3) to RC_4.
6.4 Resiliency
OSPF creates adjacencies between neighboring routers for the purpose
of exchanging routing information. After a neighbor has been
discovered, bidirectional communication is ensured, and a routing
adjacency is formed between RCs, loss of communication may result in
partitioned areas.
Consider for instance (see Figure 1.) the case where RC_1a and RC 1b
is configured for exchanging routing information downward and upward
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Area Y, resp., and that RC_2a and RC_2b are not configured for
exchanging routing any routing information toward Area X. If the
communication between RC 1a and RC 2a is broken (due e.g. to RC 5 -
RC 6 communication failure), Area Y could be partitioned.
In these conditions, it is RECOMMENDED that RC 2a to be re-
configurable such as to allow for exchanging routing information
downward to Area X. This reconfiguration MAY be performed manually
or automatically using the mechanism described in Section 6.2.
Manual reconfiguration MUST be supported.
6.5 Neighbor Relationship and Routing Adjacency
It is assumed that (point-to-point) IP control channels are
provisioned/configured between RCs belonging to the same routing
level. Provisioning/configuration techniques are outside the scope
of this document.
Once established, the OSPF Hello Protocol is responsible for
establishing and maintaining neighbor relationships. This protocol
also ensures that communication between neighbors is bidirectional.
Routing adjacency can subsequently be formed between RCs following
mechanisms defined in [RFC2328].
7. OSPFv2 Extensions
7.1 Compatibility
Extensions specified in this document are associated to the
Opaque TE LSA:
o) Router Address top level TLV (Type 1):
- Associated Area ID sub-TLV: optional sub-TLV for loop avoidance
(see Section 6.2)
o) Link top level TLV (Type 2):
- Local and Remote TE Router ID sub-TLV: optional sub-TLV for
scoping link attributes per TE_Router ID
- Associated Area ID sub-TLV: optional sub-TLV for loop avoidance
(see Section 6.2)
o) Node Attribute top level TLV (Type TBD):
- Node IPv4 Local Prefix sub-TLV: optional sub-TLV for IPv4
reachability advertisement
- Node IPv6 Local Prefix sub-TLV: optional sub-TLV for IPv6
reachability advertisement
- Local TE Router ID sub-TLV: optional sub-TLV for scoping
reachability per TE_Router ID
- Associated Area ID sub-TLV: optional sub-TLV for loop avoidance
(see Section 6.3)
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Opaque RI LSA:
o) Routing information dissemination
- U bit in Capability Descriptor TLV [OSPF-CAP]
- D bit in Capability Descriptor TLV [OSPF-CAP]
- Downstream Associated Area ID TLV in the OSPF Routing
Information LSA [OSPF-CAP]
7.2 Scalability
o) Routing information exchange upward/downward the hierarchy
between adjacent areas SHOULD by default be limited to reachability.
In addition, several transformation such as prefix aggregation are
recommended when allowing decreasing the amount of information
imported/exported by a given RC without impacting consistency.
o) Routing information exchange upward/downward the hierarchy when
involving TE attributes MUST be under strict policy control. Pacing
and min/max thresholds for triggered updates are strongly
recommended.
o) The number of routing levels MUST be maintained under strict
policy control.
8. Acknowledgements
The authors would like to thank Dean Cheng, Acee Lindem, Pandian
Vijay, Alan Davey and Adrian Farrel for their useful comments and
suggestions.
9. References
9.1 Normative References
[OSPF-NODE] R.Aggarwal, and K.Kompella, "Advertising a Router's
Local Addresses in OSPF TE Extensions," Internet Draft,
(work in progress), draft-ietf-ospf-te-node-addr-
02.txt, March 2005.
[OSPF-CAP] A.Lindem et al. "Extensions to OSPF for Advertising
Optional Router Capabilities", Work in progress, draft-
ietf-ospf-cap-08.txt, November 2005.
[RFC2026] S.Bradner, "The Internet Standards Process --
Revision 3", BCP 9, RFC 2026, October 1996.
[RFC2328] J.Moy, "OSPF Version 2", RFC 2328, April 1998.
[RFC2370] R.Coltun, "The OSPF Opaque LSA Option", RFC 2370, July
1998.
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draft-dimitri-ccamp-gmpls-ason-routing-ospf-02.txt October 2006
[RFC2740] R.Coltun et al. "OSPF for IPv6", RFC 2740, December
1999.
[RFC2119] S.Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3477] K.Kompella et al. "Signalling Unnumbered Links in
Resource ReSerVation Protocol - Traffic Engineering
(RSVP-TE)", RFC 3477, January 2003.
[RFC3630] D.Katz et al. "Traffic Engineering (TE) Extensions to
OSPF Version 2", RFC 3630, September 2003.
[RFC3667] S.Bradner, "IETF Rights in Contributions", BCP 78,
RFC 3667, February 2004.
[RFC3668] S.Bradner, Ed., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3668, February 2004.
[RFC3946] E.Mannie, and D.Papadimitriou, (Editors) et al.,
"Generalized Multi-Protocol Label Switching Extensions
for SONET and SDH Control," RFC 3946, October 2004.
[RFC4202] Kompella, K. (Editor) et al., "Routing Extensions in
Support of Generalized MPLS," RFC 4202, October 2005.
[RFC4203] Kompella, K. (Editor) et al., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)," RFC 4203, October 2005.
8.2 Informative References
[ASON-EVAL] C.Hopps et al. "Evaluation of existing Routing Protocols
against ASON Routing Requirements", Work in progress,
draft-ietf-ccamp-gmpls-ason-routing-eval-03.txt, May
2006.
[OSPF-TE-CAP]J.P. Vasseur et al. , "Routing extensions for discovery
of Traffic Engineering Node Capabilities", Work in
progress, draft-ietf-ccamp-te-node-cap-01.txt, June 2006
[RFC4258] D.Brungard et al. "Requirements for Generalized MPLS
(GMPLS) Routing for Automatically Switched Optical
Network (ASON)," RFC 4258, November 2005.
For information on the availability of ITU Documents, please see
http://www.itu.int
[G.7715] ITU-T Rec. G.7715/Y.1306, "Architecture and
Requirements for the Automatically Switched Optical
Network (ASON)," June 2002.
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[G.7715.1] ITU-T Draft Rec. G.7715.1/Y.1706.1, "ASON Routing
Architecture and Requirements for Link State Protocols,"
November 2003.
[G.8080] ITU-T Rec. G.8080/Y.1304, "Architecture for the
Automatically Switched Optical Network (ASON),"
November 2001 (and Revision, January 2003).
9. Author's Addresses
Dimitri Papadimitriou (Alcatel)
Francis Wellensplein 1,
B-2018 Antwerpen, Belgium
Phone: +32 3 2408491
EMail: dimitri.papadimitriou@alcatel.be
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Appendix 1: ASON Terminology
This document makes use of the following terms:
Administrative domain: (see Recommendation G.805) for the purposes of
[G7715.1] an administrative domain represents the extent of resources
which belong to a single player such as a network operator, a service
provider, or an end-user. Administrative domains of different players
do not overlap amongst themselves.
Control plane: performs the call control and connection control
functions. Through signaling, the control plane sets up and releases
connections, and may restore a connection in case of a failure.
(Control) Domain: represents a collection of (control) entities that
are grouped for a particular purpose. The control plane is subdivided
into domains matching administrative domains. Within an
administrative domain, further subdivisions of the control plane are
recursively applied. A routing control domain is an abstract entity
that hides the details of the RC distribution.
External NNI (E-NNI): interfaces are located between protocol
controllers between control domains.
Internal NNI (I-NNI): interfaces are located between protocol
controllers within control domains.
Link: (see Recommendation G.805) a "topological component" which
describes a fixed relationship between a "subnetwork" or "access
group" and another "subnetwork" or "access group". Links are not
limited to being provided by a single server trail.
Management plane: performs management functions for the Transport
Plane, the control plane and the system as a whole. It also provides
coordination between all the planes. The following management
functional areas are performed in the management plane: performance,
fault, configuration, accounting and security management
Management domain: (see Recommendation G.805) a management domain
defines a collection of managed objects which are grouped to meet
organizational requirements according to geography, technology,
policy or other structure, and for a number of functional areas such
as configuration, security, (FCAPS), for the purpose of providing
control in a consistent manner. Management domains can be disjoint,
contained or overlapping. As such the resources within an
administrative domain can be distributed into several possible
overlapping management domains. The same resource can therefore
belong to several management domains simultaneously, but a management
domain shall not cross the border of an administrative domain.
Subnetwork Point (SNP): The SNP is a control plane abstraction that
represents an actual or potential transport plane resource. SNPs (in
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different subnetwork partitions) may represent the same transport
resource. A one-to-one correspondence should not be assumed.
Subnetwork Point Pool (SNPP): A set of SNPs that are grouped together
for the purposes of routing.
Termination Connection Point (TCP): A TCP represents the output of a
Trail Termination function or the input to a Trail Termination Sink
function.
Transport plane: provides bi-directional or unidirectional transfer
of user information, from one location to another. It can also
provide transfer of some control and network management information.
The Transport Plane is layered; it is equivalent to the Transport
Network defined in G.805 Recommendation.
User Network Interface (UNI): interfaces are located between protocol
controllers between a user and a control domain. Note: there is no
routing function associated with a UNI reference point.
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Appendix 2: ASON Routing Terminology
This document makes use of the following terms:
Routing Area (RA): a RA represents a partition of the data plane and
its identifier is used within the control plane as the representation
of this partition. Per [G.8080] a RA is defined by a set of sub-
networks, the links that interconnect them, and the interfaces
representing the ends of the links exiting that RA. A RA may contain
smaller RAs inter-connected by links. The limit of subdivision
results in a RA that contains two sub-networks interconnected by a
single link.
Routing Database (RDB): repository for the local topology, network
topology, reachability, and other routing information that is updated
as part of the routing information exchange and may additionally
contain information that is configured. The RDB may contain routing
information for more than one Routing Area (RA).
Routing Components: ASON routing architecture functions. These
functions can be classified as protocol independent (Link Resource
Manager or LRM, Routing Controller or RC) and protocol specific
(Protocol Controller or PC).
Routing Controller (RC): handles (abstract) information needed for
routing and the routing information exchange with peering RCs by
operating on the RDB. The RC has access to a view of the RDB. The RC
is protocol independent.
Note: Since the RDB may contain routing information pertaining to
multiple RAs (and possibly to multiple layer networks), the RCs
accessing the RDB may share the routing information.
Link Resource Manager (LRM): supplies all the relevant component and
TE link information to the RC. It informs the RC about any state
changes of the link resources it controls.
Protocol Controller (PC): handles protocol specific message exchanges
according to the reference point over which the information is
exchanged (e.g. E-NNI, I-NNI), and internal exchanges with the RC.
The PC function is protocol dependent.
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