Internet DRAFT - draft-ietf-l2vpn-arp-mediation
draft-ietf-l2vpn-arp-mediation
L2VPN Working Group Himanshu Shah(Ciena)
Intended Status: Proposed Standard Eric Rosen(Cisco)
Internet Draft Giles Heron(Cisco)
Expires: July 10, 2012 Vach Kompella(Alcatel-Lucent)
January 10 2012
ARP Mediation for IP Interworking of Layer 2 VPN
draft-ietf-l2vpn-arp-mediation-19.txt
Status of this Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on July 10, 2012
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described
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without warranty as described in the Simplified BSD License.
Abstract
The Virtual Private Wire Service (VPWS) [RFC4664] 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
pseudowire (connecting the two PEs). In general, the Attachment
Circuits must be of the same technology (e.g., both Ethernet,
both ATM), and the pseudowire 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 pseudowire 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.
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 [RFC2119].
Table of Contents
Copyright Notice........................................... 1
1. Introduction............................................... 4
2. ARP Mediation (AM) function................................ 6
3. IP Layer 2 Interworking Circuit............................ 7
4. IP Address Discovery Mechanisms............................ 7
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4.1. Discovery of IP Addresses of Locally Attached IPv4 CE. 8
4.1.1. Monitoring Local Traffic......................... 8
4.1.2. CE Devices Using ARP............................. 8
4.1.3. CE Devices Using Inverse ARP.................... 10
4.1.4. CE Devices Using PPP............................ 10
4.1.5. Router Discovery method......................... 11
4.1.6. Manual Configuration............................ 12
4.2. How a CE Learns the IPv4 address of a remote CE...... 12
4.2.1. CE Devices Using ARP............................ 12
4.2.2. CE Devices Using Inverse ARP.................... 13
4.2.3. CE Devices Using PPP............................ 13
4.3. Discovery of IP Addresses of IPv6 CE Devices......... 13
4.3.1. Distinguishing Factors Between IPv4 and IPv6.... 13
4.3.2. Requirements for PEs............................ 14
4.3.3. Processing of Neighbor Solicitations............ 15
4.3.4. Processing of Neighbor Advertisements........... 15
4.3.5. Processing Inverse Neighbor Solicitations (INS). 16
4.3.6. Processing of Inverse Neighbor Advertisements .. 17
4.3.7. Processing of Router Solicitations.............. 18
4.3.8. Processing of Router Advertisements............. 18
4.3.9. Duplicate Address Detection..................... 18
4.3.10. CE address discovery for CEs attached using PPP 19
5. CE IPv4 Address Signaling between PEs..................... 19
5.1. When to Signal an IPv4 address of a CE............... 19
5.2. LDP Based Distribution of CE IPv4 Addresses.......... 20
6. IPv6 Capability Advertisement............................. 22
6.1. PW Operational Down on Stack Capability Mis-Match.... 23
6.2. Stack Capability Fall-back........................... 24
7. IANA Considerations....................................... 25
7.1. LDP Status messages.................................. 25
7.2. Interface Parameters................................. 25
8. Security Considerations................................... 26
8.1. Control Plane Security............................... 26
8.2. Data plane security.................................. 27
9. Acknowledgements.......................................... 27
10. References............................................... 27
10.1. Normative References................................ 27
10.2. Informative References.............................. 29
11. Authors' Addresses....................................... 29
APPENDIX A:.................................................. 32
A.1. Use of IGPs with IP L2 Interworking L2VPNs........... 32
A.1.1. OSPF............................................ 32
A.1.2. RIP............................................. 33
A.1.3. IS-IS........................................... 33
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1. Introduction
Layer 2 Virtual Private Networks (L2VPN) are constructed over a
Service Provider IP/MPLS 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 circuits. 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 Frame Relay, 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.
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+-----+
+------ -----| CE3 |
|AC3 +-----+
+-----+
......| 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 IPv4 CE would use ARP
[RFC826] and a Frame Relay-attached CE might use Inverse ARP
[RFC2390]. 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.
In this document, 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.
The document uses "ARP" terminology to mean any protocol that is
used to resolve IP addresses to link layer addresses. For
instance in IPv4, ARP and Inverse ARP protocols are used for
address resolution while in IPv6 Neighbor Discovery [RFC4861]
and Inverse Neighbor Discovery protocol [RFC3122] based on
ICMPv6 are used for address resolution.
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2. 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 a 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, the
ARP Mediation procedure depends on whether the packets being
forwarded are IPv4 or IPV6. A PE that is to perform ARP
Mediation for IPv4 packets MUST perform the following logical
steps:
1. Discover the IP address of the locally attached CE device
2. Terminate, do not forward ARP and Inverse ARP requests
from the CE device at the local PE.
3. Distribute the IP Address to the remote PE using
pseudowire control signaling.
4. Notify the locally attached CE of the IP address of the
remote CE.
5. Respond appropriately to ARP and Inverse ARP requests from
the local CE device, using IP address of the remote CE and
the hardware address of the local PE.
A PE that is to perform ARP Mediation for IPv6 packets SHOULD
perform the following logical steps:
1. Discover the IPv6 addresses of the locally attached CE device,
together with those of the remote CE device.
2.
a. Intercept Neighbor Discovery (ND) and Inverse Neighbor
Discovery (IND) packets received from the local CE
device.
b. From these NB and IND packets learn the IPv6
configuration of the CE.
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c. Forward the ND and IND packets over the pseudowire to the
remote PE.
3. Intercept Neighbor Discovery and Inverse Neighbor Discovery
packets received over the pseudowire from the remote PE,
possibly modifying them (if required for the type of outgoing
AC) before forwarding to the local CE, and also learning
information about the IPv6 configuration of the remote CE.
Details for the above-described procedures are given in the
following sections.
3. IP Layer 2 Interworking Circuit
The IP Layer 2 interworking Circuit refers to interconnection of
the Attachment Circuit with the IP Layer 2 Transport pseudowire
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 packet) over the pseudowire with or
without the optional control word. If the IP packet arrives at
the ingress PE with multiple data link headers (for example in
the case of bridged Ethernet PDU on an ATM Attachment Circuit),
all data link headers MUST be removed from the IP packet before
transmission over the PW. 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 pseudowire is
described in [RFC4447]. The "IP Layer 2 interworking circuit"
pseudowire is also referred to as "IP pseudowire" in this
document.
In the case of an IPv6 L2 Interworking Circuit, the egress PE
MAY modify the contents of Neighbor Discovery or Inverse
Neighbor Discovery packets before encapsulating the IP packet
with the data link header.
4. IP Address Discovery Mechanisms
An IP Layer 2 Interworking Circuit enters monitoring state
immediately after configuration. During this state it performs
two functions.
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- Discovery of the CE IP device(s)
- 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 the local CE IP device has not been discovered,
only broadcast/multicast IP frames are propagated between the
Attachment Circuit and pseudowire; unicast IP datagrams are
dropped. The IP destination address is used to classify
unicast/multicast packets.
Unicast IP frames are propagated between the AC and pseudowire
only when CE IP devices on both Attachment Circuits have been
discovered, notified and proxy functions have completed.
The need to wait for address resolution completion before
unicast IP traffic can flow is simple.
. PEs do not perform routing operations
. The destination IP address in the packet is not necessarily
that of the attached CE
. On a broadcast link, there is no way to find out the MAC
address of the CE based on the Destination IP address of
the packet.
4.1. Discovery of IP Addresses of Locally Attached IPv4 CE
A PE MUST support manual configuration of IPv4 CE addresses.
This section also describes automated mechanisms by which a PE
MAY also discover an IPv4 CE address.
4.1.1. 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.
4.1.2. CE Devices Using ARP
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If a CE device uses ARP to determine the IP address to MAC
address binding of its neighbor, the PE processes the ARP
requests to learn the IP address of the local CE for the local
Attachment Circuit.
This document mandates that there MUST be only one CE per
Attachment Circuit. However, customer facing access topologies
may exist whereby more than one CE appears 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 the PE MAY
optionally use the following selection criteria. In either case,
manual configuration of the IP address of the local CE (and its
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 IP address of the remote CE.
o Augment cross checking with the local IP address learned
through listening for link local multicast packets (as per
section 4.1.1. above).
o Augment cross checking with the local IP address learned
through the Router Discovery protocol (as described below
in section 4.1.5. ).
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 the local CE. Note that
the operator does not have to configure the IP address of
the remote CE (as that would be learned through pseudowire
signaling).
Once the local and remote CEs have been discovered for the given
Attachment Circuit, the local PE responds with its own MAC
address to any subsequent ARP requests from the local CE with a
destination IP address matching the IP address of the remote CE.
The local PE signals the IP address of the local CE to the
remote PE and MAY initiate an unsolicited ARP response to notify
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the IP address to MAC address binding for the remote CE to the
local CE (again using its own MAC address).
Once the ARP mediation function is completed (i.e. the PE device
knows both the local and remote CE IP addresses), unicast IP
frames are propagated between the AC and the established PW.
The PE MAY periodically generate ARP request messages for the IP
address of the CE as a means of verifying the continued
existence of the IP address and its MAC address binding. The
absence of a response from the CE device for a given number of
retries could be used as a trigger for withdrawal of the IP
address advertisement to the remote PE. The local PE would then
re-enter the address resolution phase to rediscover the IP
address of the attached CE. Note that this "heartbeat" scheme is
needed only where the failure of a CE device may otherwise be
undetectable.
4.1.3. 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
from the Attachment Circuit and responds with an Inverse ARP
reply containing the IP address of the remote CE, if the address
is known. If the PE does not yet have the IP address of the
remote CE, it does not respond, but records 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 an Inverse ARP request as a means of notifying the IP
address of the remote CE to the local CE.
This is the typical mode of operation for Frame Relay and ATM
Attachment Circuits. If the CE does not use Inverse ARP, the PE
can still discover the IP address of the local CE using the
mechanisms described in section 4.1.1. and 4.1.5.
4.1.4. CE Devices Using PPP
The IP Control Protocol [RFC1332] describes a procedure to
establish and configure IP on a point-to-point connection,
including the negotiation of IP addresses. When such an
Attachment Circuit is configured for IP interworking, PPP
negotiation is not performed end-to-end between CE devices.
Instead, PPP negotiation takes place between the CE and its
local PE. The PE performs proxy PPP negotiation and informs the
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attached CE of the IP address of the remote CE during IPCP
negotiation using the IP-Address option (0x03).
When a PPP link completes LCP negotiations, the local PE MAY
perform the following IPCP actions:
o The PE learns the IP address of the local CE from the
Configure-Request received with the IP-Address option
(0x03). If the IP address is non-zero, the PE records the
address and responds with Configure-Ack. However, if the
IP address is zero, the PE responds with Configure-Reject
(as this is a request from the CE to assign it an IP
address). Also, the IP address option is set with zero
value in the Configure-Reject response to instruct the CE
not to include that option in any subsequent Configure-
Request.
o If the PE receives a Configure-Request without the IP-
Address option, it responds with a Configure-Ack. In this
case the PE is unable to learn the IP address of the local
CE using IPCP and hence MUST rely on other means as
described in sections 4.1.1. and 4.1.5. Note that in
order to employ other learning mechanisms, the IPCP
negotiations MUST have reached the open state.
o If the PE does not know the IP address of the remote CE,
it sends a Configure-Request without the IP-Address
option.
o If the PE knows the IP address of the remote CE, it sends
a Configure-Request with the IP-Address option containing
the IP address of the remote CE.
The IPCP IP-Address option MAY be negotiated between the PE and
the local CE device. Configuration of other IPCP options 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.
4.1.5. 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 [RFC1256] whereby a Router Discovery Request (ICMP -
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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) are necessary.
The use of the Router Discovery method by the PE is optional.
4.1.6. Manual Configuration
In some cases, it may not be possible to discover the IP address
of the local CE device using the mechanisms described in
sections 4.1 - 4.1.5 above. In such cases manual configuration
MAY be used. All implementations of this document MUST support
manual configuration of the IPv4 address of the local CE. This
is the only REQUIRED mode for a PE to support.
The support for configuration of the IP address of the remote CE
is OPTIONAL.
4.2. How a CE Learns the IPv4 address of a remote CE
Once the local PE has received the IP address information of the
remote CE from the remote PE, it will either initiate an address
resolution request or respond to an outstanding request from the
attached CE device.
In the event that IPv4 address of the remote CE is manually
configured, the address resolution can begin immediately as
receipt of remote IP address of the CE becomes unnecessary.
4.2.1. CE Devices Using ARP
When the PE learns the IP address of the remote CE as described
in section 5.1 below, it may or may not already know the IP
address of the local CE. If the IP address is not known, the PE
MUST wait until it is acquired through one of the methods
described in sections 4.1.1, 4.1.2 and 4.1.5. 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 IP address of the remote CE with the PE's own MAC
address.
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When the local CE generates an ARP request, the PE MUST proxy
the ARP response [RFC925] using its own MAC address as the
source hardware address and the IP address of the remote CE as
the source protocol address. The PE MUST respond only to those
ARP requests whose destination protocol address matches the IP
address of the remote CE.
4.2.2. CE Devices Using Inverse ARP
When the PE learns the IP address of the remote CE, it SHOULD
generate an Inverse ARP request. If the Attachment Circuit
requires activation (e.g. Frame Relay) the PE SHOULD activate it
first before the Inverse ARP request. It should be noted, that
the PE might never receive the response to its own request, nor
see any Inverse ARP request from the CE, in cases where the CE
is pre-configured with the IP address of the remote CE or where
the use of Inverse ARP has not been enabled. In either case the
CE has used other means to learn the IP address of its neighbor.
4.2.3. CE Devices Using PPP
When the PE learns the IP address of the remote CE, it SHOULD
initiate a Configure-Request and set the IP-Address option to
the IP address of the remote CE to notify the IP address of the
remote CE to the local CE.
4.3. Discovery of IP Addresses of IPv6 CE Devices
4.3.1. Distinguishing Factors Between IPv4 and IPv6
IPv4 uses ARP and inverse ARP to resolve IP address and link
layer associations. Since these are dedicated address resolution
protocols, and not IP packets, they cannot be carried on an IP
pseudowire. They MUST be processed locally and the IPv4 address
information they carry signaled between the PEs using the
pseudowire control plane. IPv6 uses ICMPv6 extensions to resolve
IP address and link address associations. As these are IPv6
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packets they can be carried on an IP pseudowire and therefore no
IPv6 address signaling is required.
4.3.2. Requirements for PEs
A PE device that supports IPv6 MUST be capable of,
- Intercepting ICMPv6 Neighbor Discovery [RFC4861] and
Inverse Neighbor Discovery [RFC3122] packets received over
the AC as well as over the PW.
- Recording the IPv6 interface addresses and CE link-layer
addresses present in these packets
- Possibly modifying these packets as dictated by the data
link type of the egress AC (described in the following
sections), and
- Forwarding them towards the original destination
The PE MUST also be capable of generating packets in order to
interwork between Neighbor Discovery (ND) and Inverse Neighbor
Discovery (IND). This is specified in Sections 4.3.3 to 4.3.6
below.
If an IP PW is used to interconnect CEs that use IPv6 Router
Discovery [RFC4861], a PE device MUST also be capable of
intercepting and processing those Router Discovery packets. This
is required in order to translate between different link layer
addresses. If a Router Discovery message contains a link layer
address, then the PE MAY also use this message to discover the
link layer address and IPv6 interface address. This is described
in more detail in Section 4.3.7 and Section 4.3.8.
The PE device MUST learn a list of CE IPv6 interface addresses
for its directly-attached CE and another list of CE IPv6
interface addresses for the far-end CE. The PE device MUST also
learn the link-layer address of the local CE and be able to use
it when forwarding traffic between the local and far-end CEs.
The PE MAY also wish to monitor the source link-layer address of
data packets received from the CE, and discard packets not
matching its learned CE link-layer address.
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4.3.3. Processing of Neighbor Solicitations
A Neighbor Solicitation received on an AC from a local CE SHOULD
be inspected to determine and learn an IPv6 interface address
(if provided, this will not be the case for Duplicate Address
Detection) and any link-layer address provided. The packet MUST
then be forwarded over the pseudowire unmodified. A Neighbor
Solicitation received over the pseudowire SHOULD be inspected to
determine and learn an IPv6 interface address for the far-end
CE. If a source link-layer address option is present, the PE
MUST remove it. The PE MAY substitute an appropriate link-layer
address option, specifying the link-layer address of the PE
interface attached to the local AC. Note that if the local AC is
Ethernet, failure to substitute a link-layer address option may
mean that the CE has no valid link-layer address with which to
transmit data packets.
When a PE with a local AC, which is of the type point-to-point
layer 2 circuit e.g. FR, ATM or PPP, receives a Neighbor
Solicitation from a far end PE over the pseudowire, after
learning the IP address of the far-end CE, the PE MAY use one of
the following procedures:
1. Forward the Neighbor Solicitation to the local CE after
replacing the source link-layer address with the link-
layer address of the local AC.
2. Send an Inverse Neighbor Solicitation to the local CE,
specifying the far-end CE's IP address and the link-layer
address of the local AC.
3. Reply to the far end PE with a Neighbor Advertisement,
using the IP address of the local CE as the source address
and an appropriate link-layer address option that
specifies the link-layer address of the local AC. As
described later, the IP address of the local CE is learned
through IPv6CP in the case of PPP and through Neighbor
Solicitation in other cases.
4.3.4. Processing of Neighbor Advertisements
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A Neighbor Advertisement received on an AC from a local CE
SHOULD be inspected to determine and learn an IPv6 interface
address and any link-layer address provided. The packet MUST
then be forwarded over the IP pseudowire unmodified.
A Neighbor Advertisement received over the pseudowire SHOULD be
inspected to determine and learn an IPv6 interface address for
the far-end CE. If a source link-layer address option is
present, the PE MUST remove it. The PE MAY substitute an
appropriate link-layer address option, specifying the link-layer
address of the local AC. Note that if the local AC is Ethernet,
failure to substitute a link-layer address option may mean that
the local AC has no valid link-layer address with which to
transmit data packets.
When a PE with a local AC which is of the type point-to-point
layer 2 circuit, such as ATM, FR or PPP, receives a Neighbor
Advertisement over the pseudowire, in addition to learning the
remote CE's IPv6 address, it SHOULD perform the following steps:
o If the AC supports Inverse Neighbor Discovery (IND) and
the PE had already processed an Inverse Neighbor
Solicitation (INS) from local CE, it SHOULD send an
Inverse Neighbor Advertisement (INA) on the local AC using
source IP address information received in ND-ADV and its
own local AC link layer information.
o If the PE has not received any Inverse Neighbor
Solicitation (INS) from the local CE, and the AC supports
Inverse Neighbor Discovery (IND), it SHOULD send an INS on
the local AC using source IP address information received
in the INA together with its own local AC link layer
information.
4.3.5. Processing Inverse Neighbor Solicitations (INS)
An INS received on an AC from a local CE SHOULD be inspected to
determine and learn the IPv6 addresses and the link-layer
addresses. The packet MUST then be forwarded over the pseudowire
unmodified.
An INS received over the pseudowire SHOULD be inspected to
determine and learn one or more IPv6 addresses for the far-end
CE. If the local AC supports IND (e.g., a switched Frame Relay
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AC), the packet SHOULD be forwarded to the local CE, after
modifying the link-layer address options to match the type of
the local AC.
If the local AC does not support IND, processing of the packet
depends on whether the PE has learned at least one interface
address for its directly-attached CE.
. If it has learned at least one IPv6 address for the CE, the
PE MUST discard the Inverse Neighbor Solicitation (INS) and
generate an Inverse Neighbor Advertisement (INA) back into
the pseudowire. The destination address of the INA is the
source address from the INS, the source address is one of
the local CE's interface addresses, and all the local CE's
interface addresses that have been learned so far SHOULD be
included in the Target Address List. The Source and Target
Link-Layer addresses are copied from the INS. In addition,
the PE SHOULD generate ND advertisements on the local AC
using the IPv6 address of the remote CE and link-layer
address of the local PE.
. If it has not learned at least one IPv6 and link-layer
address of its directly-connected CE, the INS MUST be
continued to be discarded until the PE learns an IPv6 and
link-layer address from the local CE (through receiving,
for example, a Neighbor Solicitation). After this has
occurred, the PE will be able to respond to INS messages
received over the pseudowire as described above.
4.3.6. Processing of Inverse Neighbor Advertisements (INA)
An INA received on an AC from a local CE SHOULD be inspected to
determine and learn one or more IPv6 addresses for the CE. It
MUST then be forwarded unmodified over the pseudowire.
An INA received over the pseudowire SHOULD be inspected to
determine and learn one or more IPv6 addresses for the far-end
CE.
If the local AC supports IND (e.g., a Frame Relay AC), the
packet MAY be forwarded to the local CE, after modifying the
link-layer address options to match the type of the local AC.
If the local AC does not support IND, the PE MUST discard the
INA and generate a Neighbor Advertisement (NA) towards its local
CE. The source IPv6 address of the NA is the source IPv6 address
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from the INA, the destination IPv6 address is the destination
IPv6 address from the INA and the link-layer address is that of
the local AC on the PE.
4.3.7. Processing of Router Solicitations
A Router Solicitation received on an AC from a local CE SHOULD
be inspected to determine and learn an IPv6 address for the CE,
and, if present, the link-layer address of the CE. It MUST then
be forwarded unmodified over the pseudowire.
A Router Solicitation received over the pseudowire SHOULD be
inspected to determine and learn an IPv6 address for the far-end
CE. If a source link-layer address option is present, the PE
MUST remove it. The PE MAY substitute a source link-layer
address option specifying the link-layer address of its local
AC. The packet is then forwarded to the local CE.
4.3.8. Processing of Router Advertisements
A Router Advertisement received on an AC from a local CE SHOULD
be inspected to determine and learn an IPv6 address for the CE,
and, if present, the link-layer address of the CE. It MUST then
be forwarded unmodified over the pseudowire.
A Router Advertisement received over the pseudowire SHOULD be
inspected to determine and learn an IPv6 address for the far-end
CE. If a source link-layer address option is present, the PE
MUST remove it. The PE MAY substitute a source link-layer
address option specifying the link-layer address of its local
AC. If an MTU option is present, the PE MAY reduce the specified
MTU if the MTU of the pseudowire is less than the value
specified in the option. The packet is then forwarded to the
local CE.
4.3.9. Duplicate Address Detection
Duplicate Address Detection [RFC4862] allows IPv6 hosts and
routers to ensure that the addresses assigned to interfaces are
unique on a link. As with all Neighbor Discovery packets, those
used in Duplicate Address Detection will simply flow through the
pseudowire, being inspected at the PEs at each end, processing
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is performed as above. However, the source IPv6 address of
Neighbor Solicitations used in Duplicate Address Detection is
the unspecified address, so the PEs cannot learn the CE's IPv6
interface address (nor would it make sense to do so, given that
at least one address is tentative at that time).
4.3.10. CE address discovery for CEs attached using PPP
The IPv6 Control Protocol (IPv6CP) [RFC5072] describes a
procedure to establish and configure IPv6 on a point-to-point
connection, including the negotiation of a link-local interface
identifier. As in the case of IPv4, when such an AC is
configured for IP interworking, PPP negotiation is not performed
end-to-end between CE devices. Instead, PPP negotiation takes
place between the CE and its local PE. The PE performs proxy PPP
negotiation and informs the attached CE of the link-local
identifier of its local interface using the Interface-Identifier
option (0x01). This local interface identifier is used by
stateless address auto configuration [RFC4862].
When a PPP link completes IPv6CP negotiations and the PPP link
is open, a PE MAY discover the IPv6 unicast address of the CE
using any of the mechanisms described above.
5. CE IPv4 Address Signaling between PEs
5.1. When to Signal an IPv4 address of a CE
A PE device advertises the IPv4 address of the attached CE only
when the encapsulation type of the pseudowire is IP Layer2
Transport (the value 0x0000B, as defined in [RFC4446]). The IP
Layer2 transport PW is also referred to as IP PW and is used
interchangeably in this document. It is quite possible that the
IPv4 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 IPv4 address along with the PW FEC from the remote PE, a
deadlock situation arises. In order to avoid such problems, the
PE MUST be prepared to advertise the PW FEC before the IPv4
address of the CE is known and hence uses IPv4 address value
zero. When the IPv4 address of the CE device does become
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available, the PE re-advertises the PW FEC along with the IPv4
address of the CE.
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 IP address of the CE. The receiving PE then waits
for notification of the remote IP address. During this period,
propagation of unicast IPv4 traffic is suspended, but multicast
IPv4 traffic can continue to flow between the AC and the
pseudowire.
If two CE devices are locally attached to the PE on disparate AC
types (for example, one CE connected to an Ethernet port and the
other to a Frame Relay port), the IPv4 addresses are learned in
the same manner as described above. However, since the CE
devices are local, the distribution of IPv4 addresses for these
CE devices is a local step.
Note that the PEs discover the IPv6 addresses of the remote CE
by intercepting Neighbor Discovery and Inverse Neighbor
Discovery packets that have been passed in-band through the
pseudowire. Hence, there is no need to communicate the IPv6
addresses of the CEs through LDP signaling.
If the pseudowire is carrying both IPv4 and IPv6 traffic, the
mechanisms used for IPV6 and IPv4 SHOULD NOT interact. In
particular, just because a PE has learned a link-layer address
for IPv6 traffic by intercepting a Neighbor Advertisement from
its directly-connected CE, it SHOULD NOT assume that it can use
that link-layer address for IPv4 traffic until that fact is
confirmed by reception of, for example, an IPv4 ARP message from
the CE.
5.2. LDP Based Distribution of CE IPv4 Addresses
[RFC4447] uses Label Distribution Protocol (LDP) transport to
exchange PW FECs 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.
In addition to PW-FEC, this document uses an IP Address List TLV
(as defined in [RFC5036]) that is to 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
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parameters in the Label Mapping message to extend the attributes
of the PW FEC is specified in [RFC4447].
As defined in [RFC4447], when processing a received PW FEC, the
PE matches the PW ID and PW type with the locally configured PW
ID and PW Type. If there is a match and if the PW Type is IP
Layer2 Transport, the PE further checks for the presence of an
Address List TLV [RFC5036] in the optional parameter TLVs. The
processing of the Address List TLV is as follows.
o If a PE is configured for an AC to a CE enabled for IPv4
or dual-stack IPv4/IPv6, the PE SHOULD advertise an
Address List TLV with address family type of IPv4 address.
The PE SHOULD process the IPv4 Address List TLV as
described in this document. The PE MUST advertise and
process IPv6 capability using the procedures described in
Section 6 below.
o If a PE does not receive any IPv4 address in the Address
List TLV it MAY assume IPv4 behavior. The address
resolution for IPv4 MUST then depend on local manual
configuration. In the case of mis-matched configuration
whereby one PE has manual configuration while other does
not, the IP address to Link Layer address mapping remains
unresolved resulting into unsuccessful propagation of IPv4
traffic to the local CE.
o If a PE is configured for an AC to a CE enabled for IPv6
only, the PE MUST advertise IPv6 capability using the
procedures described in Section 6 below. In addition, by
virtue of not setting the manual configuration for IPv4
support, an IPv6 only support is realized.
We use the Address List TLV [RFC5036] to signal the IPv4 address
of the local CE. This IP Address List TLV is included in the
optional parameter field of the Label Mapping message.
The Address List TLV is only used for IPv4 addresses.
The fields of the IP Address List TLV are set as follows:
Length
Set to 6 to encompass 2 bytes of Address Family field and 4
bytes of Addresses field (because a single IPv4 address is
used).
Address Family
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Set to 1 to indicate IPv4 as defined in [RFC5036].
Addresses
Contains a single IPv4 address that is the address of the
CE attached to the advertising PE.
The address in the Addresses field is set to all zeros to denote
that the advertising PE has not learned the IPv4 address of its
local CE. Any non-zero address value denotes the IPv4 address of
the advertising PE's attached CE device.
The IPv4 address of the CE is also supplied in the optional
parameters field of the LDP Notification message along with the
PW FEC. The LDP Notification message is used to signal any
change in the status of the CE's IPv4 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 List TLV (as defined above) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PWId FEC or Generalized ID FEC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Status TLV status code is set to 0x0000002C "IP address of
CE", to indicate that an IP Address update follows. Since this
notification does not refer to any particular message the
Message ID field is set to 0.
The PW FEC TLV SHOULD NOT include the interface parameters as
they are ignored in the context of this message.
6. IPv6 Capability Advertisement
A 'Stack Capability' Interface Parameter sub-TLV is signaled by
the two PEs so that they can agree which network protocol(s)
they SHOULD be using. As discussed earlier, the use of Address-
List TLV signifies the support for IPv4 stack, so the 'Stack
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Capability' sub-TLV is used to indicate whether support for IPv6
stack is required on a given IP PW.
The 'Stack Capability' sub-TLV is part of the interface
parameters. The proposed format for the Stack Capability
Interface Parameter sub-TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter ID | Length | Stack Capability |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Parameter ID = 0x16
Length = 4
The Stack Capability field is a bit field. Only one bit is
defined in this document. When bit zero (the least significant
bit with bitmask 0x0001) is set, it indicates IPv6 stack
capability.
The presence of stack capability TLV is relevant only when the
PW type is IP PW. A PE that supports the IPv6 on an IP PW MUST
signal the Stack Capability sub-TLV in the initial Label Mapping
message for the PW. The PE nodes compare the value advertised by
the remote PE with the local configuration and only use a
capability which is supported by both.
The behavior of a PE that does not understand an Interface
Parameter sub-TLV is specified in section 5.5 of RFC 4447
[RFC4447].
In some deployment scenarios, it may be desirable to take a PW
operationally down if there is a mismatch of the Stack
Capability between the PEs. In other deployment scenarios, an
operator may wish the IP version supported by both PEs to fall-
back to IPv4 if one of the PEs does not support IPv6. The
following procedures MUST be followed for each of these cases.
6.1. PW Operational Down on Stack Capability Mis-Match
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If a PE that supports IPv6 and has not yet sent a Label Mapping,
receives an initial Label Mapping message from the far end PE
that does not include the 'Stack Capability' sub-TLV, or one is
received but it is not set to 'IPv6 Stack Capability' value,
then the PE supporting this procedure MUST NOT send a Label
Mapping for this PW.
If a PE that supports IPv6 has already sent an initial Label
Mapping message for the PW and does not receive a 'Stack
Capability' sub-TLV in the Label Mapping message from the far-
end PE, or one is received but it is not set to 'IPv6 Stack
Capability', the PE supporting this procedure MUST withdraw its
PW label with the LDP status code meaning "IP Address type
mismatch" (Status Code 0x0000004A). However, subsequently if the
configuration was to change at the far-end PE and a 'Stack
Capability' sub-TLV in the Label Mapping message is received
from the far-end PE, the local PE MUST re-advertise the Label
Mapping message for the PW.
6.2. Stack Capability Fall-back
If a PE that supports IPv6 and has not yet sent a Label Mapping,
receives an initial Label Mapping from the far end PE that does
not include the 'Stack Capability' sub-TLV, or one is received
but it is not set to the 'IPv6 Stack Capability' value, then it MAY
send a Label Mapping for this PW but MUST NOT include the Stack
Capability sub-TLV.
If a PE that supports IPv6 and has already sent a Label Mapping
for the PW with the 'Stack Capability' sub-TLV, but does not
receive a 'Stack Capability' sub-TLV from the far-end PE in the
initial Label Mapping message, or one is received but it is not set
to the 'IPv6 Stack Capability' value, the PE following this
procedure MUST send a Label Withdraw for its PW label with the LDP
status code meaning "Wrong IP Address type" (Status Code 0x000004B)
followed by a Label Mapping message that does not include the
'Stack Capability' sub-TLV.
If a Label Withdraw message with the "Wrong IP Address Type"
status code is received by a PE, it SHOULD treat this as a
normal Label Withdraw, but MUST NOT respond with a Label Release.
It MUST continue to wait for the next control message for the PW as
specified in section 6.2 of RFC 4447 [RFC4447].
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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
[RFC5036]. The following values are suggested for assignment:
0x0000002C "IP Address of CE"
0x0000004A "IP Address Type Mismatch"
0x0000004B "Wrong IP Address Type"
7.2. Interface Parameters
This document proposes a new Interface Parameters sub-TLV, to be
assigned from the 'Pseudowire Interface Parameters Sub-TLV type
Registry'. The following value is suggested for the Parameter ID:
0x16 "Stack Capability"
IANA is also requested to set up a registry of "L2VPN PE stack
capabilities". This is a 16 bit field. Stack Capability bitmask
0x0001 is specified in Section 6 of this document. The remaining
bitfield values (0x0002,..,0x8000) are to be assigned by IANA using
the "IETF Review" policy defined in [RFC5226].
L2VPN PE Stack Capabilities:
Bit (Value) Description
=============== ==========================================
Bit 0 (0x0001) - IPv6 stack capability
Bit 1 (0x0002) - Reserved
Bit 2 (0x0004) - Reserved
.
.
.
Bit 14 (0x4000) - Reserved
Bit 15 (0x8000) - Reserved
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8. Security Considerations
The security aspect of this solution is addressed for two
planes; control plane and data plane.
8.1. Control Plane Security
Control plane security pertains to establishing the LDP
connection, and to pseudowire signaling and CE IP address
distribution over that LDP connection. For greater security the
LDP connection between two trusted PEs MUST be secured by each
PE verifying the incoming connection against the configured
address of the peer and authenticating the LDP messages using
MD5 authentication, as described in section 2.9 of [RFC5036].
Pseudowire signaling between two secure LDP peers does not pose
a security issue but mis-wiring could occur due to configuration
error. However, the fact that the pseudowire will only be
established if the two PEs have matching configurations (e.g. PW
ID, PW type, and MTU) provides some protection against mis-
wiring due to configuration errors.
Learning the IP address of the appropriate CE can be a security
issue. It is expected that the Attachment Circuit to the local
CE will be physically secured. If this is a concern, the PE MUST
be configured with IP and MAC address of the CE when connected
with Ethernet or IP and virtual circuit information (DLCI or
VPI/VCI) when connected over Frame Relay or ATM and IP address
only when connected over PPP. During ARP/inverse ARP frame
processing, the PE MUST verify the received information against
local configuration before forwarding the information to the
remote PE to protect against hijacking of the connection.
For IPv6, the preferred means of security is Secure Neighbor
Discovery (SEND) [RFC3971]. SEND provides a mechanism for
securing Neighbor Discovery packets over media (such as wireless
links) that may be insecure and open to packet interception and
substitution. SEND is based upon cryptographic signatures of
Neighbor Discovery packets. These signatures allow the receiving
node to detect packet modification and confirm that a received
packet originated from the claimed source node. SEND is
incompatible with the Neighbor Discovery packet modifications
described in this document. As such, SEND cannot be used for
Neighbor Discovery across an ARP Mediation pseudowire. PEs
taking part in IPv6 ARP Mediation MUST remove all SEND packet
options from Neighbor Discovery packets before forwarding into
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the pseudowire. If the CE devices are configured to accept only
SEND Neighbor Discovery packets, this will lead to Neighbor
Discovery failing. Thus, the CE devices MUST be configured to
accept non-SEND packets, even if they treat them with lower
priority than SEND packets. Because SEND cannot be used in
combination with IPv6 ARP Mediation, it is suggested that IPv6
ARP Mediation is only used with secure Attachment Circuits.
An exception to this recommendation applies to an implementation
that supports the SEND Proxy [SPROXY] experimental draft which
allows a device such as PEs to act as an ND proxy as described
in [SPROXY].
8.2. 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, the 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 the PW only when authenticity is verified. When spoofing is
detected, the PE MUST sever the connection with the local CE,
tear down the PW and start over.
9. 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 document.
10. References
10.1. Normative References
[RFC826] 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".
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[RFC2390] RFC 2390, T. Bradley et al., "Inverse Address
Resolution Protocol".
[RFC4447] L. Martini et al., "Pseudowire Setup and
Maintenance using LDP", RFC 4447.
[RFC4446] L. Martini et al,. "IANA Allocations for pseudo
Wire Edge to Edge Emulation (PWE3)", RFC 4446.
[RFC2119] S.Bradner, "Key words for use in RFCs to indicate
requirement levels", RFC 2119.
[RFC5036] L.Anderseen et al., "LDP Specification", RFC
5036.
[RFC4861] Narten, T., Nordmark, E. and W.Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 4861.
[RFC3122] Conta, A., "Extensions to IPv6 Neighbor Discovery
for Inverse Discovery Specification", RFC 3122.
[RFC4862] Thomson, S. and Narten, T., "IPv6 Stateless
Address Autoconfiguration", RFC 4862.
[RFC3971] Arkko, J. et al., "Secure Neighbor Discovery
(SEND)", RFC 3971.
[RFC5226] Narten, T et al., "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 5226.
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10.2. Informative References
[RFC4664] L. Andersson et al., "Framework for L2VPN", RFC
4664.
[RFC1332] G. McGregor, "The PPP Internet Protocol Control
Protocol (IPCP)", RFC 1332.
[RFC5072] D. Haskin, "IP Version 6 over PPP", RFC 5072.
[RFC925] J.Postel, "Multi-LAN Address Resolution", RFC
925.
[RFC1256] S.Deering, "ICMP Router Discovery Messages", RFC
1256.
[RFC5309] Shen and Zinin, "Point-to-point operation over
LAN in Link State Routing Protocols", RFC 5309.
[SPROXY] S.Krishnan et al., "Secure Proxy ND support for
SEND", draft-ietf-csi-proxy-send-05.txt
11. Authors' Addresses
This document is the combined effort of many who have
contributed, carefully reviewed and provided the technical
clarifications for the document.
Himanshu Shah (editor)
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Ciena
Email: hshah@ciena.com
Eric Rosen (editor)
Cisco Systems
Email: erosen@cisco.com
Giles Heron
Cisco Systems (editor)
Email: giheron@cisco.com
Vach Kompella (editor)
Alcatel-Lucent
Email: vach.kompella@alcatel-lucent.com
Matthew Bocci
Alcatel-Lucent
Email: Mathew.bocci@alcatel-lucent.com
Tiberiu Grigoriu
Alcatel-Lucent
Email: Tiberiu.Grigoriu@alcatel-lucent.com
Neil Hart
Alcatel-Lucent
Email: Neil.Hart@alcatel-lucent.com
Andrew Dolganow
Alcatel-Lucent
Email: Andrew.Dolganow@alcatel-lucent.com
Shane Amante
Level 3
Email: Shane@castlepoint.net
Toby Smith
Google
EMail: tob@google.com
Andrew G. Malis
Verizon
EMail: Andy.g.Malis@verizon.com
Steven Wright
Bell South Corp
Email: steven.wright@bellsouth.com
Waldemar Augustyn
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Consultant
Email: waldemar@wdmsys.com
Arun Vishwanathan
Juniper Networks
Email: arunvn@juniper.net
Ashwin Moranganti
IneoQuest Technologies
Email: Ashwin.Moranganti@Ineoquest.com
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APPENDIX A:
A.1. 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.
The point to point operations of the routing protocols over a
LAN is discussed in [RFC5309].
A.1.1. 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 each other router on the link forms
adjacencies. However, these procedures are neither 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 the two cross-connected routers.
Finally, each OSPF router generates network LSAs when connected
to a broadcast link such as Ethernet, receipt of which by an
OSPF router which believes itself to be connected to a 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. The point-to-point operation of the routing
protocol over
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A.1.2. RIP
RIP protocol broadcasts RIP advertisements every 30 seconds. If
the multicast/broadcast traffic snooping mechanism is used as
described in section 4.1, the attached PE can learn the local CE
router's IP address from the IP header of its advertisements. No
special configuration is required for RIP in this type of Layer
2 IP Interworking L2VPN.
A.1.3. IS-IS
The IS-IS protocol does not encapsulate its PDUs in IP, and
hence cannot be supported in IP L2 Interworking L2VPNs.
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