L2VPN Working Group Himanshu Shah Ciena Corp
Internet Draft Eric Rosen Cisco System
Giles Heron Tellabs
Vach Kompella Alcatel
June 2006
Expires: December 2006
ARP Mediation for IP Interworking of Layer 2 VPN
draft-ietf-l2vpn-arp-mediation-05.txt
Status of this Memo
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This Internet-Draft will expire on December 2006.
IPR Disclosure Acknowledgement
By submitting this Internet-Draft, each author represents that
any applicable patent or other IPR claims of which he or she is
aware have been or will be disclosed, and any of which he or she
becomes aware will be disclosed, in accordance with Section 6 of
BCP 79.
Abstract
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The VPWS service [L2VPN-FRM] provides point-to-point connections
between pairs of Customer Edge (CE) devices. It does so by binding
two Attachment Circuits (each connecting a CE device with a Provider
Edge, PE, device) to a pseudo-wire (connecting the two PEs). In
general, the Attachment Circuits must be of the same technology
(e.g., both Ethernet, both ATM), and the pseudo-wire must carry the
frames of that technology. However, if it is known that the frames'
payload consists solely of IP datagrams, it is possible to provide a
point-to-point connection in which the pseudo-wire connects
Attachment Circuits of different technologies. This requires the PEs
to perform a function known as "ARP Mediation". ARP Mediation refers
to the process of resolving Layer 2 addresses when different
resolution protocols are used on either Attachment Circuit. The
methods described in this document are applicable even when the CEs
run a routing protocol between them, as long as the routing protocol
runs over IP. In particular, the applicability of ARP mediation to
ISIS is not addressed as IS-IS PDUs are not sent over IP.
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].
Table of Contents
IPR Disclosure Acknowledgement.........Error! Bookmark not defined.
1. Contributing Authors...........................................3
2. Introduction...................................................4
3. ARP Mediation (AM) function....................................5
4. IP Layer 2 Interworking Circuit................................5
5. Discovery of IP Addresses of Locally Attached CE Device........6
5.1. Monitoring Local Traffic..................................6
5.2. CE Devices Using ARP......................................6
5.3. CE Devices Using Inverse ARP..............................8
5.4. CE Devices Using PPP......................................8
5.5. Router Discovery method...................................9
6. CE IP Address Signaling between PEs...........................10
6.1. When to Signal an IP address of a CE.....................10
6.2. LDP Based Distribution...................................10
6.3. Out-of-band Distribution Configuration...................12
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7. IANA Considerations...........................................13
7.1. LDP Status messages......................................13
8. How a CE Learns the Remote CE's IP address....................13
8.1. CE Devices Using ARP.....................................13
8.2. CE Devices Using Inverse ARP.............................14
8.3. CE Devices Using PPP.....................................14
9. Use of IGPs with IP L2 Interworking L2VPNs....................14
9.1. OSPF.....................................................14
9.2. RIP......................................................15
10. IPV6 Considerations..........................................15
11. Multi-Segment PW consideration...............................15
12. Security Considerations......................................16
12.1. Control plane security..................................16
12.2. Data plane security.....................................17
13. Acknowledgements.............................................17
14. References...................................................17
14.1. Normative References....................................17
14.2. Informative References..................................18
15. Authors' Addresses...........................................18
Intellectual Property Statement..................................19
Disclaimer of Validity...........................................20
Copyright Statement....................Error! Bookmark not defined.
1. Contributing Authors
This document is the combined effort of the following individuals
and many others who have carefully reviewed the document and
provided the technical clarifications.
W. Augustyn consultant
T. Smith Laurel Networks
A. Moranganti Big Band Networks
S. Khandekar Alcatel
A. Malis Tellabs
S. Wright Bell South
V. Radoaca Westridge Networks
A. Vishwanathan Force10 Networks
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2. Introduction
Layer 2 Virtual Private Networks (L2VPN) are constructed over a
Service Provider IP backbone but are presented to the Customer Edge
(CE) devices as Layer 2 networks. In theory, L2VPNs can carry any
Layer 3 protocol, but in many cases, the Layer 3 protocol is IP.
Thus it makes sense to consider procedures that are optimized for
IP.
In a typical implementation, illustrated in the diagram below, the
CE devices are connected to the Provider Edge (PE) devices via
Attachment Circuits (AC). The ACs are Layer 2 links. In a pure
L2VPN, if traffic sent from CE1 via AC1 reaches CE2 via AC2, both
ACs would have to be of the same type (i.e., both Ethernet, both FR,
etc.). However, if it is known that only IP traffic will be carried,
the ACs can be of different technologies, provided that the PEs
provide the appropriate procedures to allow the proper transfer of
IP packets.
+-----+
+--------------------| CE3 |
| +-----+
+-----+
........| PE3 |.........
. +-----+ .
. | .
. | .
+-----+ AC1 +-----+ Service +-----+ AC2 +-----+
| CE1 |-----| PE1 |--- Provider ---| PE2 |-----| CE2 |
+-----+ +-----+ Backbone +-----+ +-----+
. .
........................
A CE, which is connected via a given type of AC, may use an IP
Address Resolution procedure that is specific to that type of AC.
For example, an Ethernet-attached CE would use ARP [ARP] and a FR-
attached CE might use Inverse ARP [INVARP]. If we are to allow the
two CEs to have a Layer 2 connection between them, even though each
AC uses a different Layer 2 technology, the PEs must intercept and
"mediate" the Layer 2 specific address resolution procedures.
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In this draft, we specify the procedures for VPWS services, which
the PEs must implement in order to mediate the IP address resolution
mechanism. We call these procedures "ARP Mediation".
Consider a Virtual Private Wire Service (VPWS) constructed between
CE1 and CE2 in the diagram above. If AC1 and AC2 are of different
technologies, e.g. AC1 is Ethernet and AC2 is Frame Relay (FR), then
ARP requests coming from CE1 cannot be passed transparently to CE2.
PE1 must interpret the meaning of the ARP requests and mediate the
necessary information with PE2 before responding.
3. ARP Mediation (AM) function
The ARP Mediation (AM) function is an element of a PE node that
deals with the IP address resolution for CE devices connected via an
VPWS L2VPN. By placing this function in the PE node, ARP Mediation
is transparent to the CE devices.
For a given point-to-point connection between a pair of CEs, a PE
must perform three logical steps as part of the ARP Mediation
procedure:
1. Discover the IP addresses of the locally attached CE device
2. Terminate, do not distribute ARP and Inverse ARP requests from CE
device(s) at local PE.
3. Distribute those IP Addresses to the remote PE
4. Notify the locally attached CE of the remote CE's IP address.
This information is gathered using the mechanisms described in the
following sections.
4. IP Layer 2 Interworking Circuit
The IP Layer 2 interworking Circuit refers to interconnection of the
Attachment Circuit with the IP Layer 2 Transport pseudo-wire that
carries IP datagrams as the payload. The ingress PE removes the
data link header of its local Attachment Circuit and transmits the
payload (an IP frame) over the pseudo-wire with or without the
optional control word. In some cases, multiple data link headers may
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exist, such as bridged PDU on ATM AC. In this case, ATM header as
well as the Ethernet header is removed to expose the IP frame. The
egress PE encapsulates the IP packet with the data link header used
on its local Attachment Circuit.
The encapsulation for the IP Layer 2 Transport pseudo-wire is
described in [PWE3-Control].
5. Discovery of IP Addresses of Locally Attached CE Device
An IP Layer 2 Interworking Circuit enters monitoring state
immediately after the configuration. During this state it performs
two functions.
o Discovery of locally attached CE IP device
o Establishment of the PW
The establishment of the PW occurs independently from local CE IP
address discovery. During the period when the PW has been
established but local CE IP device has not been detected, only
broadcast/multicast IP frames are propagated between the Attachment
Circuit and pseudo-wire; unicast IP datagrams are dropped. On
Ethernet AC, MAC Destination Address is used to classify
unicast/multicast packets. However, on non-Ethernet ACs, IP
destination address is used to classify unicast/multicast packets.
The unicast IP frames are propagated between AC and pseudo-wire only
when CE IP devices on both Attachment Circuits have been discovered,
notified and proxy functions have completed.
5.1. Monitoring Local Traffic
The PE devices may learn the IP addresses of the locally attached
CEs from any IP traffic, such as link local multicast packets (e.g.,
destined to 224.0.0.x), and are not restricted to the operations
below.
5.2. CE Devices Using ARP
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If a CE device uses ARP to determine the MAC address to IP address
binding of its neighbor, the PE processes the ARP requests to learn
the IP address of local CE for the stated locally attached circuit.
This document mandates that only one CE per attachment circuit MUST
be connected to the PE. However, customer facing access topology may
exist whereby more than one CEs appear to be connected to the PE on
a single attachment circuit. For example this could be the case when
CEs are connected to a shared LAN that connects to the PE. In such
case, the PE MUST select one local CE. The selection could be based
on manual configuration or PE may optionally use following selection
criteria. In either case, manual configuration of local CE’s IP
address (and MAC address) MUST be supported.
o Wait to learn the IP address of the remote CE (through PW
signaling) and then select the local CE that is sending the
request for the remote CE's IP address.
o Augment cross checking with the local IP address learned through
listening of link local multicast packets (as per section 5.1
above)
o Augment cross checking with the local IP address learned through
the Router Discovery protocol (as described below in section
5.5).
o There is still a possibility that the local PE may not receive an
IP address advertisement from the remote PE and there may exist
multiple local IP routers that attempt to 'connect' to remote
CEs. In this situation, the local PE may use some other criteria
to select one IP device from many (such as "the first ARP
received"), or an operator may configure the IP address of local
CE. Note that the operator does not have to configure the IP
address of the remote CE (as that would be learned through
pseudo-wire signaling).
Once the local CE has been discovered for the given Attachment
Circuit, the local PE responds to subsequent ARP requests from that
device with its own MAC address when the destination IP address in
the ARP request is found to match with the remote CE's IP address.
The local PE signals the CE's IP address to the remote PE and may
initiate an unsolicited ARP response to notify local CE MAC address
to IP address binding of the remote CE. Once the ARP mediation
function is completed, unicast IP frames are propagated between the
AC and the established PW.
The PE may periodically generate ARP request messages to the CE's
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IP address as a means of verifying the continued existence of the
address and its binding to the MAC address. The absence of a
response from the CE device for a given number of retries could be
used as a cause for withdrawal of the IP address advertisement to
the remote PE. The local PE would then enter into the address
resolution phase to rediscover the attached CE's IP address. Note
that this "heartbeat" scheme is needed only for broadcast links
(such as Ethernet AC), as the loss of a CE may otherwise be
undetectable.
5.3. CE Devices Using Inverse ARP
If a CE device uses Inverse ARP to determine the IP address of its
neighbor, the attached PE processes the Inverse ARP request for
stated circuit and responds with an Inverse ARP reply containing the
remote CE's IP address, if the address is known. If the PE does not
yet have the remote CE's IP address, it does not respond, but notes
the IP address of the local CE and the circuit information.
Subsequently, when the IP address of the remote CE becomes
available, the PE may initiate the Inverse ARP request as a means to
notify the local CE about the IP address of the remote CE.
This is a typical operation for Frame Relay and ATM attachment
circuits. When the CE does not use Inverse ARP, PE could still
discover the IP address of local CE as described in section 5.1 and
5.5
5.4. CE Devices Using PPP
The IP Control Protocol [PPP-IPCP] describes a procedure to
establish and configure IP on a point-to-point connection, including
the negotiation of IP addresses. When using IP (Routed) mode L2VPN
interworking, PPP negotiation is not performed end-to-end between
CE devices. In this case, PPP negotiation takes place between the CE
device and its local PE device (on the PPP attachment circuit). The
PE device performs proxy PPP negotiation, and informs the local CE
device of the IP address of the remote CE device during IPCP
negotiation using the IP-Address option [0x03].
When a PPP link becomes operational after the LCP negotiations, the
local PE MAY perform following actions
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o The PE learns the IP address of the local CE from the Configure-
Request received with the IP-Address option (0x03). The PE
verifies that the IP address present in the IP-Address option is
non-zero. If the IP address is zero, PE responds with Configure-
Reject (as this is a request from CE to assign him an IP
address). Also, the Configure-Reject copies the IP-Address option
with null value to instruct the CE to not include that option in
new Configure-Request. If the IP address is non-zero, PE responds
with Configure-Ack.
o If the PE receives Configure-Request without the IP-Address
option, PE responds with Configure-Ack. In this case, PE would
not learn the IP address of the local CE using IPCP and hence
would rely on other means as described above (such as link-local
broadcast from OSPF hello). Note that in order to employ other
learning mechanisms, IPCP connection must be open.
o If the PE does not know the IP address of the remote CE, it
generates a Configure-Request without the IP-Address option.
o If the PE knows the IP address of the remote CE, it sends an IPCP
Configure-Request with the IP-Address option containing the
remote CE's IP address.
The IPCP IP-Address option MAY be negotiated between the PE and the
local CE device. Configuration of other IPCP option MAY be rejected.
Other NCPs, with the exception of the Compression Control Protocol
(CCP) and Encryption Control Protocol (ECP), MUST be rejected. The
PE device MAY reject configuration of the CCP and ECP.
5.5. Router Discovery method
In order to learn the IP address of the CE device for a given
Attachment Circuit, the PE device may execute Router Discovery
Protocol [RFC 1256] whereby a Router Discovery Request (ICMP -
router solicitation) message is sent using a source IP address of
zero. The IP address of the CE device is extracted from the Router
Discovery Response (ICMP - router advertisement) message from the
CE. It is possible that the response contains more than one router
addresses with the same preference level; in which case, some
heuristics (such as first on the list) is necessary.
The use of the Router Discovery method by the PE is optional.
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6. CE IP Address Signaling between PEs
6.1. When to Signal an IP address of a CE
A PE device advertises the IP address of the attached CE only when
the encapsulation type of the pseudo-wire is IP Layer2 Transport
(the value 0x0000B, as defined in [PWE3-IANA]). It is quite
possible that the IP address of a CE device is not available at the
time the PW labels are signaled. For example, in Frame Relay the CE
device sends an inverse ARP request only when the DLCI is active; if
the PE signals the DLCI to be active only when it has received the
IP address along with the PW FEC from the remote PE, a chicken and
egg situation arises. In order to avoid such problems, the PE must
be prepared to advertise the PW FEC before the CE's IP address is
known and hence uses IP address value zero. When the IP address of
the CE device does become available, the PE re-advertises the PW FEC
along with the CE's IP address.
Similarly, if the PE detects that an IP address of a CE is no longer
valid (by methods described above), the PE must re-advertise the PW
FEC with null IP address to denote the withdrawal of the CE's IP
address. The receiving PE then waits for notification of the remote
IP address. During this period, propagation of unicast IP traffic is
suspended, but multicast IP traffic can continue to flow between the
AC and the pseudo-wire.
If two CE devices are locally attached to the PE where one CE is
connected to an Ethernet port and the other to a Frame Relay port,
for example, the IP addresses are learned in the same manner
described above. However, since the CE devices are local, the
distribution of IP addresses for these CE devices is a local step.
6.2. LDP Based Distribution
The [PWE3-Control] uses Label Distribution Protocol (LDP) transport
to exchange PW FEC in the Label Mapping message in the Downstream
Unsolicited (DU) mode. The PW FEC comes in two flavors; PWid and
Generalized ID FEC elements and has some common fields between them.
The discussions below refer to these common fields for IP L2
Interworking encapsulation.
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In addition to PW-FEC, this document defines an IP address TLV that
must be included in the optional parameter field of the Label
Mapping message when advertising the PW FEC for the IP Layer2
Transport. The use of optional parameters in the Label Mapping
message to extend the attributes of the PW FEC is specified in the
[PWE3-Control].
When processing a received PW FEC, the PE matches the PW Id and PW
type with the locally configured PW Id to determine if the PW FEC
is of type IP Layer2 Transport. If there is a match, it further
checks the presence of IP address TLV in the optional parameter
field. If absent, a Label Release message is issued with a Status
Code meaning "IP Address of the CE is absent" [note: Status Code
0x0000002C is pending IANA allocation] to reject the PW
establishment.
We use the Address List TLV as defined in RFC 3036 to signal the IP
address of the local CE. This IP address TLV must be included in the
optional parameter field of the Label Mapping message.
Encoding of the IP Address TLV is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Address List (0x0101) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Family | CE's IP Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ CE's IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length
When Address Family is IPV4, Length is equal to 6 bytes; 2 bytes
for address family and 4 bytes of IP address.
Address Family
Two octet quantity containing a value from the ADDRESS FAMILY
NUMBERS from ADDRESS FAMILY NUMBERS in [RFC 1700] that encodes the
address contained in the Address field.
CE's IP Address
IP address of the CE attached to the advertising PE. The
encoding of the individual address depends on the Address Family.
The following address encodings are defined by this version of the
protocol:
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Address Family Address Encoding
IPv4 (1) 4 octet full IPv4 address
IPv6 (2) 16 octet full IPv6 address
The IP address field is set to value null to denote that advertising
PE has not learned the IP address of his local CE device. The non-
zero value of the IP address field denotes IP address of advertising
PE's attached CE device.
The CE's IP address is also supplied in the optional parameter field
of the LDP's Notification message along with the PW FEC. The LDP
Notification message is used to signal the change in CE's IP
address.
The encoding of the LDP Notification message is 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Notification (0x0001) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status (TLV) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address TLV (as defined above) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PWId FEC or Generalized ID FEC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Status TLV status code is set to 0x0000002B "IP address of CE",
to indicate that IP Address update follows. Since this notification
does not refer to any particular message the Message Id, and Message
Type fields are set to 0. [note: Status Code 0x0000002B is pending
IANA allocation].
The PW FEC TLV SHOULD not include the interface parameters as they
are ignored in the context of this message.
6.3. Out-of-band Distribution Configuration
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In some cases, it may not be possible either to deduce the IP
addresses from the VPN traffic nor induce remote PEs to supply the
necessary information on demand. For those cases, out-of-band
methods, such as manual configuration, MAY be used. The support for
manual configuration of the local CE’s IP address is mandatory.
7. IANA Considerations
7.1. LDP Status messages
This document uses new LDP status codes, IANA already maintains a
registry of name "STATUS CODE NAME SPACE" defined by RFC3036. The
following values are suggested for assignment:
0x0000002B "IP Address of CE"
0x0000002C "IP Address of CE is absent"
8. How a CE Learns the Remote CE's IP address
Once the local PE has received the remote CE's IP address
information from the remote PE, it will either initiate an address
resolution request or respond to an outstanding request from the
attached CE device.
8.1. CE Devices Using ARP
When the PE learns the remote CE's IP address as described in
section 6.1 and 6.2, it may or may not know the local CE's IP
address. If the local CE's IP address is not known, the PE must wait
until it is acquired through one of the methods described in
sections 5.1, 5.3 and 5.5. If the IP address of the local CE is
known, the PE may choose to generate an unsolicited ARP message to
notify the local CE about the binding of the remote CE's IP address
with the PE's own MAC address.
When the local CE generates an ARP request, the PE must proxy the
ARP response [PROXY-ARP] using its own MAC address as the source
hardware address and remote CE's IP address as the source protocol
address. The PE must respond only to those ARP requests whose
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destination protocol address matches the remote CE's IP address. An
exception to this rule is when the strict topology of one IP end
station per Attachment Circuit is assumed. In which case, PE can
promiscuously respond to the CE's ARP request with his own MAC
address.
8.2. CE Devices Using Inverse ARP
When the PE learns the remote CE's IP address, it should generate an
Inverse ARP request. In case, the local circuit requires activation
e.g. Frame Relay, PE should activate it first before sending Inverse
ARP request. It should be noted, that PE might never receive the
response to its own request, nor see any CE's Inverse ARP request in
cases where CE is pre-configured with remote CE IP address or the
use of Inverse ARP is not enabled. In either case CE has used other
means to learn the IP address of his neighbor.
8.3. CE Devices Using PPP
When the PE learns the remote CE's IP address, it should initiate
the Configure-Request and set the IP-Address option to the remote
CE's IP address to notify local CE the IP address of the remote CE.
9. Use of IGPs with IP L2 Interworking L2VPNs
In an IP L2 interworking L2VPN, when an IGP on a CE connected to a
broadcast link is cross-connected with an IGP on a CE connected to a
point-to-point link, there are routing protocol related issues that
must be addressed. The link state routing protocols are cognizant of
the underlying link characteristics and behave accordingly when
establishing neighbor adjacencies, representing the network
topology, and passing protocol packets.
9.1. OSPF
The OSPF protocol treats a broadcast link type with a special
procedure that engages in neighbor discovery to elect a designated
and a backup designated router (DR and BDR respectively) with which
it forms adjacencies. However, these procedures are neither
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applicable nor understood by OSPF running on a point-to-point link.
By cross-connecting two neighbors with disparate link types, an IP
L2 interworking L2VPN may experience connectivity issues.
Additionally, the link type specified in the router LSA will not
match for two routers that are supposedly sharing the same link
type. Finally, each OSPF router generates network LSAs when
connected to a broadcast link such as Ethernet, receipt of which by
an OSPF router on the point-to-point link further adds to the
confusion.
Fortunately, the OSPF protocol provides a configuration option
(ospfIfType), whereby OSPF will treat the underlying physical
broadcast link as a point-to-point link.
It is strongly recommended that all OSPF protocols on CE devices
connected to Ethernet interfaces use this configuration option when
attached to a PE that is participating in an IP L2 Interworking VPN.
9.2. RIP
RIP protocol broadcasts RIP advertisements every 30 seconds. If the
group/broadcast address snooping mechanism is used as described
above, the attached PE can learn the advertising (CE) router's IP
address from the IP header of the advertisement. No special
configuration is required for RIP in this type of Layer 2 IP
Interworking L2VPN.
10. IPV6 Considerations
The support for IPV6 is not addressed in this draft and is for
future study.
11. Multi-Segment PW consideration
In a back-to-back configuration, when two PEs are connected with an
Ethernet, ARP proxy function has limited application, as there is no
local CE. Consider a network configuration whereby PE1 in network A
is connected to CE1 and PE4 in network B is connected to CE2. The
PE2 on network A is connected to PE3 in network B directly with an
Ethernet. Since there is no CE present between PE2 and PE3, there
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needs a mechanism for PE2 and PE3 to discover each other’s MAC
address to enable connectivity between CE1 and CE2 across the two
networks. There are two options.
. Configure CE2’s IP address as a local CE’s IP address at PE2
and CE1’s IP address as local CE’s IP address at PE3.
Additionally, PE2 and PE3 are required to generate ARP requests
using their own MAC addresses as the source address. These PEs
are in effect proxying for CEs present in the each other’s
network. This is not a desirable option as it requires
configuration of IP address of a CE that is present in others
(possibly other service provider’s) network.
. The second option is to follow the procedures recommended in
[MS-PW] architecture, which provides the intervening or
switching PEs to remain oblivious to native PW processing. We
recommend this option.
12. Security Considerations
The security aspect of this solution is addressed for two planes;
control plane and data plane.
12.1. Control plane security
The control plane security pertains to establishing the LDP
connection, pseudo-wire establishment and CE's IP address
distribution. The LDP connection between two trusted PEs can be
achieved by each PE verifying the incoming connection against the
configured peer's address and authenticating the LDP messages using
MD5 authentication. The pseudo-wire establishments between two
secure LDP peers do not pose security issue but mis-wiring could
occur due to configuration error. Some checks, such as, proper
pseudo-wire type and other pseudo-wire options may prevent mis-
wiring due to configuration errors.
The learning of the appropriate CE's IP address can be a security
issue. It is expected that the local attachment circuit to CE is
physically secured. If this is a concern, the PE must be configured
with CE's IP and MAC address when connected with Ethernet or CE's IP
and virtual circuit information (e.g. DLCI or VPI/VCI). During each
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ARP/inARP frame processing, PE must verify the received information
against the configuration before accepting to protect against
hijacking the connection.
12.2. Data plane security
The data traffic between CE and PE is not encrypted and it is
possible that in an insecure environment, a malicious user may tap
into the CE to PE connection and generate traffic using the spoofed
destination MAC address on the Ethernet Attachment Circuit. In order
to avoid such hijacking, local PE may verify the source MAC address
of the received frame against the MAC address of the admitted
connection. The frame is forwarded to PW only when authenticity is
verified. When spoofing is detected, PE must sever the connection
with the local CE, tear down the PW and start over.
13. Acknowledgements
The authors would like to thank Yetik Serbest, Prabhu Kavi, Bruce
Lasley, Mark Lewis, Carlos Pignataro and other folks who
participated in the discussions related to this draft.
14. References
14.1. Normative References
[ARP] RFC 826, STD 37, D. Plummer, "An Ethernet Address Resolution
protocol: Or Converting Network Protocol Addresses to 48.bit
Ethernet Addresses for Transmission on Ethernet Hardware".
[INVARP] RFC 2390, T. Bradley et al., "Inverse Address Resolution
Protocol".
[PWE3-Control] L. Martini et al., "Pseudowire Setup and Maintenance
using LDP", RFC 4447.
[PWE3-IANA] L. Martini et al,. "IANA Allocations for pseudo Wire
Edge to Edge Emulation (PWE3)", RFC 4446.
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[MS-PW] M.Bocci et al,. "An Architecture for Multi-Segment Pseudo
Wire Emulation Edge-to-Edge", May 2006, work in progress
[RFC 1700] Reynolds and Postel, "Assigned Numbers".
[RFC 2119] S. Bradner, "Key words for use in RFCs to indicate
requirement levels".
14.2. Informative References
[L2VPN-FRM] L. Andersson et al., "Framework for L2VPN", June 2004,
work in progress.
[PPP-IPCP] RFC 1332, G. McGregor, "The PPP Internet Protocol
Control Protocol (IPCP)".
[PROXY-ARP] RFC 925, J. Postel, "Multi-LAN Address Resolution".
[RFC 1256] S.Deering, "ICMP Router Discovery Messages".
15. Authors' Addresses
Himanshu Shah
35 Nagog Park,
Acton, MA 01720
Email: hshah@ciena.com
Eric Rosen
Cisco Systems
1414 Massachusetts Avenue,
Boxborough, MA 01719
Email: erosen@cisco.com
Waldemar Augustyn
Email: waldemar@nxp.com
Giles Heron
Email: giles.heron@tellabs.com
Sunil Khandekar and Vach Kompella
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Email: sunil@timetra.com
Email: vkompella@timetra.com
Toby Smith
Laurel Networks
Omega Corporate Center
1300 Omega drive
Pittsburgh, PA 15205
Email: jsmith@laurelnetworks.com
Arun Vishwanathan
Force10 Networks
1440 McCarthy Blvd.,
Milpitas, CA 95035
Email: arun@force10networks.com
Andrew G. Malis
Tellabs
2730 Orchard Parkway
San Jose, CA 95134
Email: Andy.Malis@tellabs.com
Steven Wright
Bell South Corp
Email: steven.wright@bellsouth.com
Vasile Radoaca
Email: vasile@westridgenetworks.com
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