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Versions: (draft-shah-l2vpn-arp-mediation) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 RFC 6575

     L2VPN Working Group                         Himanshu Shah(Ciena)
     Intended Status: Proposed Standard             Eric Rosen(Cisco)
     Internet Draft                                Giles Heron(Cisco)
     Expires: September 4, 2011         Vach Kompella(Alcatel-Lucent)
     
                                                     March 04 2011
     
     
     
     
               ARP Mediation for IP Interworking of Layer 2 VPN
                    draft-ietf-l2vpn-arp-mediation-16.txt
     
     Status of this Memo
     
     This Internet-Draft is submitted in full conformance with the
     provisions of BCP 78 and BCP 79.
     
     Internet-Drafts are working documents of the Internet
     Engineering Task Force (IETF), its areas, and its working
     groups.  Note that other groups may also distribute working
     documents as Internet-Drafts.
     
     Internet-Drafts are draft documents valid for a maximum of six
     months and may be updated, replaced, or obsoleted by other
     documents at any time. It is inappropriate to use Internet-
     Drafts as reference material or to cite them other than as "work
     in progress."
     
     The list of current Internet-Drafts can be accessed at
     http://www.ietf.org/1id-abstracts.html
     
     The list of Internet-Draft Shadow Directories can be accessed at
     http://www.ietf.org/shadow.html
     
     This Internet-Draft will expire on September 4, 2011
     
     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
     
     
     
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     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.
     
     Copyright Notice
     
     Copyright (c) 2010 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
     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
     in Section 4.e of the Trust Legal Provisions and are provided
     without warranty as described in the Simplified BSD License.
     
     
     
     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........................................... 2
        1. Introduction............................................... 4
        2. ARP Mediation (AM) function................................ 6
        3. IP Layer 2 Interworking Circuit............................ 7
        4. IP Address Discovery Mechanisms............................ 7
           4.1. Discovery of IP Addresses of Locally Attached IPv4 CE. 8
     
     
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              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............ 14
              4.3.4. Processing of Neighbor Advertisements........... 15
              4.3.5. Processing Inverse Neighbor Solicitations....... 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............................. 23
           6.1. PW Operational Down on Stack Capability Mis-Match.... 24
           6.2. Stack Capability Fall-back........................... 25
        7. IANA Considerations....................................... 25
           7.1. LDP Status messages.................................. 25
           7.2. Interface Parameters................................. 26
        8. Security Considerations................................... 26
           8.1. Control Plane Security............................... 26
           8.2. Data plane security.................................. 27
        9. Acknowledgements.......................................... 28
        10. References............................................... 28
           10.1. Normative References................................ 28
           10.2. Informative References.............................. 29
        11. Authors' Addresses....................................... 30
        APPENDIX A:.................................................. 32
           A.1. Use of IGPs with IP L2 Interworking L2VPNs........... 32
              A.1.1. OSPF............................................ 32
              A.1.2. RIP............................................. 32
              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 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.
     
     
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                                          +-----+
                             +------ -----| 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 IPv4 CE would use ARP
     [RFC826] and a FR-attached CE might use Inverse ARP [RFC 2390].
     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 [RFC 4861]
     and Inverse Neighbor Discovery protocol [RFC 3122] 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 must
     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. Intercept Neighbor Discovery and Inverse Neighbor Discovery
          packets received from the local CE device, learning
          information about the IPv6 configuration of the CE, before
          forwarding the 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
     
     
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          information about the IPv6 configuration of the remote CE.
     
     PEs MUST support ARP mediation for IPv4 L2 Interworking
     circuits. PEs SHOULD support ARP mediation for IPv6 L2
     interworking circuits.
     
     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. In some cases, multiple data
     link headers may exist, such as a bridged Ethernet PDU on an ATM
     Attachment Circuit. In this case, all data link headers are
     removed to expose the IP packet at the ingress. 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 commonly referred to as "IP pseudowire".
     
     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.
     
        - Discovery of the CE IP device(s)
        - Establishment of the PW
     
     
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     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
     
     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.
     
     
     
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     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
     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.
     
     
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     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
     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:
     
     
     
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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). 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 -
     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.
     
     
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     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.
     
     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
     
     
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     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
     packets they can be carried on an IP pseudowire and therefore no
     IPv6 address signaling is required.
     
     
     
     
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     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.
     
     4.3.3. Processing of Neighbor Solicitations
     
     
     
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     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 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
     
     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.
     
     
     
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     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 and the PE
           had already processed an Inverse Neighbor Solicitation
           (IND-SOL) 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, 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
     
     An Inverse Neighbor Solicitation 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 Inverse Neighbor Solicitation 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 Inverse
     Neighbor Discovery (e.g., a switched Frame Relay 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.
     
     
     
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     If the local AC does not support Inverse Neighbor Discovery
     (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
     
     An Inverse Neighbor Advertisement (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 Inverse Neighbor Discovery (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 Inverse Neighbor Discovery, 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 from the INA, the destination IPv6
     
     
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     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
     is performed as above. However, the source IPv6 address of
     
     
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     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) [RFC 5072] 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
     chicken and egg 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
     available, the PE re-advertises the PW FEC along with the IPv4
     address of the CE.
     
     
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     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 defines an IP Address List
     TLV 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 parameters in the Label
     Mapping message to extend the attributes of the PW FEC is
     specified in [RFC4447].
     
     
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     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 (as specified in [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 as defined in [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 encoding of the IP Address List TLV is:
     
     
     
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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0| Address List (0x0101)     |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Address Family            |     IP Address of CE          ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~      IP Address of CE         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     
     Length
          6 bytes: 2 bytes for address family and 4 bytes of IPv4
          address.
     
     Address Family
          Two octet quantity containing a value from the ADDRESS
          FAMILY NUMBERS in [RFC3232] that encodes the address
          contained in the Address field.
     
     IP Address of CE
          IPv4 address of the CE attached to the advertising PE.  The
          encoding of the individual address depends on the Address
          Family (which may be of value zero).
     
     The following address encodings are defined by this version of
     the protocol:
     
                    Address Family      Address Encoding
     
                    IPv4 (1)             4 octet full IPv4 address
     
     
     The IP address field is set to all zeroes to denote that the
     advertising PE has not learned the IPv4 address of its local CE.
     Any non-zero value of the IP address field 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
     
     
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     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 and Message Type fields are 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
     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        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     
     
     
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     Parameter ID = 0x16
     
     Length = 4
     
     Stack Capability = 0x0001 to indicate IPv6 stack capability
     
     The value of Stack Capability is dependent on the PW type
     context. For IP Layer2 Transport type, a setting of 0x0001
     indicates IPv6 stack capability.
     
     A PE that supports 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
     
     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
     
     
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     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].
     
     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"
     
     
     
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     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 value
     0x0001 is specified in Section 6. of this document. The remaining
     bitfield values (0x0002,..,0x8000) are to be assigned by IANA using
     the "IETF Consensus" 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
     
     
     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. The LDP connection
     between two trusted PEs can be secured by each PE verifying the
     incoming connection against the configured address of the peer
     and authenticating the LDP messages using MD5 authentication.
     
     
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     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
     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.
     
     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
     
     
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     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".
     
        [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.
     
        [RFC 2119] S.Bradner, "Key words for use in RFCs to indicate
                   requirement levels", RFC 2119.
     
        [RFC 5036] L.Anderseen et al., "LDP Specification", RFC
                   5036.
     
     
     
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                  Draft-ietf-l2vpn-arp-mediation-16.txt
     
        [RFC 4861]  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.
     
     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.
     
     
     
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                  Draft-ietf-l2vpn-arp-mediation-16.txt
     
        [RFC1256]  S.Deering, "ICMP Router Discovery Messages", RFC
                   1256.
     
        [RFC3232]  Reynolds and Postel, "Assigned Numbers", RFC
                   3232.
     
     
     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)
     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
     
     
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     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
     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.
     
     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.
     
     A.1.2. RIP
     
     RIP protocol broadcasts RIP advertisements every 30 seconds. If
     the multicast/broadcast traffic snooping mechanism is used as
     
     
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     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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