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Versions: 00 01 02 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 7436

                                                          Himanshu Shah
                                                         Ciena Networks

                                                             Eric Rosen
                                                   Francois Le Faucheur
                                                          Cisco Systems
   PPVPN Working Group
   Internet Draft
   Draft-ietf-l2vpn-ipls-02.txt                             Giles Heron
                                                                Tellabs
   July 2005
   Expires: January 2006








                        IP-Only LAN Service (IPLS)


Status of this Memo

   By submitting this Internet-Draft, each author represents that
   any applicable patent or other IPR claims of which he or she is
   aware have been or will be disclosed, and any of which he or she
   becomes aware will be disclosed, in accordance with Section 6 of
   BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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        http://www.ietf.org/ietf/1id-abstracts.txt
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        http://www.ietf.org/shadow.html
   This Internet-Draft will expire on January 2006.

   Copyright Notice
      Copyright (C) The Internet Society (2005).  All Rights Reserved.
   For potential updates to the above required-text see:
        http://www.ietf.org/ietf/1id-guidelines.txt


Abstract


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   A Virtual Private LAN Service (VPLS) [VPLS] is used to interconnect
   systems across a wide-area or metropolitan-area network, making it
   appear that they are on a private LAN.  The systems which are
   interconnected may themselves be LAN switches.  If, however, they
   are IP hosts or IP routers, certain simplifications to the operation
   of the VPLS are possible.  We call this simplified type of VPLS an
   "IP-only LAN Service" (IPLS).  In an IPLS, as in a VPLS, LAN
   interfaces are run in promiscuous mode, and frames are forwarded
   based on their destination MAC addresses.  However, the maintenance
   of the MAC forwarding tables is done via signaling, rather than via
   the MAC address learning procedures specified in [IEEE 802.1D].
   This draft specifies the protocol extensions and procedures for
   support of the IPLS service.

Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119



   Table of Contents


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   Status of this Memo................................................1
   Abstract...........................................................1
   Table of Contents..................................................2
   1.0  Contributing Authors.........................................3
   2.0 Overview.......................................................3
   2.1 Terminology....................................................6
   3.0 Topology.......................................................7
   4.0 Configuration..................................................8
   5.0 Discovery......................................................8
   5.1 CE discovery...................................................9
   6.0 Pseudowire Creation............................................9
   6.1 Receive Unicast Multipoint-to-point Pseudowire.................9
   6.3 Send Multicast Replication tree...............................10
   7.0 Signaling.....................................................10
   7.1 IPLS PW Signaling.............................................11
   7.2 Signaling Advertisement Processing............................11
   8.0 Forwarding....................................................12
 8.1 Non-IP or non-ARP traffic......................................12
 8.2 Unicast IP Traffic.............................................12
   8.3 Broadcasts and Multicast IP Traffic...........................12
   8.4 ARP Traffic...................................................13
   8.5 Encapsulation.................................................13
   9.0   Attaching to IPLS via ATM or FR.............................14
   10.0 VPLS vs IPLS.................................................14
   11.0 IP Protocols.................................................15
   12.0 Dual Homing with IPLS........................................15
   13.0 Acknowledgements.............................................15
   14.0 Security Considerations......................................15
   15.0 References...................................................15
 15.1 Normative References..........................................15
 15.2 Informative References........................................16
   16.0 Author's Address.............................................16
   Intellectual Property Statement...................................17

1.0  Contributing Authors
   This document is the combined effort of the following individuals
   and many others who have carefully reviewed this document and
   provided the technical clarifications

   K. Arvind                    Enterasys Networks
   Vach Kompella                Alcatel
   Vasille Radoaca              Westridge Networks


2.0 Overview

   As emphasized in [VPLS], Ethernet has become popular as an access
   technology in Metropolitan and Wide Area Networks. [VPLS] describes
   how geographically dispersed customer LANs can be interconnected
   over a service provider's network. The VPLS service is provided by
   Provider Edge (PE) devices that connect Customer Edge (CE) devices.
   The VPLS architecture provides this service by incorporating
   bridging functions such as MAC address learning in the PE devices.

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   Provider Edge platforms are designed primarily to be IP routers,
   rather than to be LAN switches. To add VPLS capability to a PE
   router, one has to add MAC address learning capabilities, along with
   aging and other mechanisms native to ethernet switches. This may be
   fairly complex to add to the forwarding plane architecture of an IP
   router.  As discussed in [L2VPN-FWK], in scenarios where the CE
   devices are NOT LAN switches, but rather are IP hosts or IP routers,
   it is possible to provide the VPLS service without requiring MAC
   address learning and aging on the PE.  Instead, a PE router has to
   have the capability to match the destination MAC address in a packet
   received from a CE to an outbound pseudowire.  The requirements for
   the IPLS service are described in [L2VPN-REQTS]. The purpose of this
   document is to specify a solution optimized for IPLS.

   IPLS provides a VPLS-like service using PE routers that are not
   designed to perform general LAN bridging functions. One must be
   willing to accept the restriction that an IPLS be used for IP
   traffic only, and not used to interconnect CE devices that are
   themselves LAN switches. This is an acceptable restriction in many
   environments, given that IP is the predominant type of traffic in
   today's networks.

   In IPLS, a PE device implements multi-point LAN connectivity for IP
   traffic using the following key functions:

     1. CE Address Discovery: Each Provider Edge (PE) device discovers
        IP/MAC address associations for the locally attached Customer
        Edge (CE) devices, for each IPLS instance configured on the PE
        device.

     2. Pseudowire (PW) for Unicast Traffic: For each locally attached
        CE device in a given IPLS instance, a PE device sets up a
        pseudo-wire (PW-LSP) to each of the other PEs that supports the
        same IPLS instance.

        For instance, if PEx and PEy both support IPLS I, and PEy is
        locally attached to CEa and CEb, PEy will initiate the setup of
        two pseudowires between itself and PEx.  One of these will be
        used to carry unicast traffic from any of PEx's CE devices to
        CEa.  The other will be used to carry unicast traffic from any
        of PEx's CE devices to CEb.

        Note that these pseudowires carry traffic only in one
        direction.  Further, while the pseudowire implicitly identifies
        the destination CE of the traffic, it does not identify the
        source CE; packets from different source CEs bound to the same
        destination CE are sent on a single pseudowire.

     3. Pseudowires for Multicast Traffic:  In addition, every PE
        supporting a given IPLS instance will set up a special
        "broadcast pseudowire" to every other PE in that IPLS instance.
        If, in the above example, one of PEx's CE devices sends a

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        multicast packet, PEx would forward the multicast packet to PEy
        on the special broadcast pseudowire.  PEy would then send a
        copy of that packet to CEa and a copy to CEb.

        The broadcast pseudowire carries Ethernet frames of
        multicast/broadcast IP and ARP packets. Thus when a PE sends a
        multicast packet across the network, it sends one copy to each
        remote PE (supporting the given IPLS instance).  If a
        particular remote PE has more than one CE device in that IPLS
        instance, the remote PE must replicate the packet and send one
        copy to each of its local CEs.

        As with the pseudowires that are used for unicast traffic,
        packets travel in only one direction on these pseudowires, and
        packets from different sources may be freely intermixed.

     4. Signaling:  The necessary pseudowires can be set up and
        maintained using the LDP-based signaling procedures described
        in [PWE3-CONTROL].

        A PE may assign the same label to each of the unicast
        pseudowires that lead to a given CE device, in effect creating
        a multipoint-to-point pseudowire.

        Similarly, a PE may assign the same label to each of the
        broadcast pseudowires for a given IPLS instance, in effect
        creating a multipoint-to-point pseudowire.

        When setting up a pseudowire to be used for unicast traffic,
        the PE must also signal the IP address and the MAC address of
        the corresponding CE device.

     5. ARP Packet Forwarding: ARP packets are forwarded from
        attachment circuit to broadcast pseudowires in the Ethernet
        frame format as described by [PWE3-ETH]. Following rules are
        observed when processing ARP packets,
          a. Both broadcast (request) and unicast (response) ARP
             packets are sent over the broadcast pseudowire.
          b. When an ARP packet is received from an attachment circuit,
             the packet is copied to control plane for learning CEÆs IP
             and MAC address
          c. All Ethernet packets, including ARP packets, received from
             broadcast pseudowire are forwarded out to all the
             attachment circuits associated with the IPLS instance.
             These packets are not copied to control plane.

     6. Multicast IP packet Forwarding: An IP Ethernet frame received
        from an attachment circuit is replicated to other attachment
        circuits and the broadcast pseudowires associated with the IPLS
        instance. An IP Ethernet frame received from a broadcast
        pseudowire is replicated to all the egress attachment circuits
        associated with the IPLS instance.

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     7. Unicast IP packet Forwarding: An IP packet received from the
        attachment circuit is forwarded based on the MAC DA lookup in
        the forwarding table. If a match is found, the packet is
        forwarded to the associated egress interface. If the egress
        interface is unicast pseudowire, the packet is sent without MAC
        header. If the egress interface is a local attachment circuit
        the Ethernet frame is forwarded as such. An IP packet received
        from the unicast pseudowire is forwarded to egress attachment
        circuit with MAC header prepended. The MAC DA is derived from
        the forwarding table while PEÆs own MAC address is used as MAC
        SA.


   Both VPLS [VPLS] and IPLS require the ingress PE to forward a frame
   based on its destination MAC address. However, two key differences
   between VPLS and IPLS can be noted from the above description:

     . In VPLS, MAC entries are placed in the FIB of the ingress PE as
        a result of MAC address learning (which occurs in the data
        plane) while in IPLS MAC entries are placed in the FIB as a
        result of pseudowire signaling operations (control plane).
     . In VPLS, the egress PE looks up a frame's destination MAC
        address to determine the egress Attachment Circuit; in IPLS,
        the egress Attachment Circuit is determined entirely by the
        ingress PW-label.

   The following sections describe the details of the IPLS scheme.

2.1 Terminology


        IPLS                                    IP-only LAN service (a type of Virtual Private
                       LAN Service that is restricted to IP traffic
                       only).

        mp2p PW        Multipoint-to-Point Pseudowire. A pseudowire
                        that carries traffic from remote PE devices to
                        a PE device that signals the pseudowire. The
                        signaling PE device advertises the same PW-
                        label to all remote PE devices that participate
                        in the IPLS service instance. In IPLS, for a
                        given IPLS instance, an mp2p PW used for IP
                        unicast traffic is established by a PE for each
                        CE device locally attached to that PE. It is a
                        unidirectional tree whose leaves consist of the
                        remote PE peers (which connect at least one
                        Attachment Circuit associated with the same
                        IPLS instance) and whose root is the signaling
                        PE. Traffic flows from the leaves towards the
                        root.

        Multicast PW   Multicast/broadcast Pseudowire. A special kind
                        of mp2p PW that carries IP multicast/broadcast

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                        traffic and all ARP frames. In the IPLS
                        architecture, for each IPLS instance supported
                        by a PE, that PE device establishes exactly one
                        multicast/broadcast PW. Multicast PW uses
                        Ethernet encapsulation.
        Unicast PW     Unicast Pseudowire carries IP unicast packets.
                        A PE creates unicast PW for each locally
                        attached CE. The unicast PW uses IP Layer2
                        transport encapsulation.

        CE             Customer Edge device. In this document, a CE is
                        any IP node (host or router) connected to the
                        IPLS LAN service.

        Replication Tree The collection of all multicast PWs and
                        attachment circuits that are members of an IPLS
                        service instance on a given PE. When a PE
                        receives a multicast/broadcast packet from an
                        attachment circuit, the PE device sends a copy
                        of the packet to every broadcast pseudowire and
                        attachment circuit of the replication tree,
                        excluding the attachment circuit on which the
                        packet was received. When a PE receives a
                        packet from a multicast PW, the PE device sends
                        a copy of the packet to all the attachment
                        circuits of the replication tree and never to
                        other PWs.

3.0 Topology

   The Customer Edge (CE) devices are IP nodes (hosts or routers) that
   are connected to PE devices either directly, or via an Ethernet
   network. We assume that the PE/CE connection may be regarded by the
   PE as an "interface" to which one or more CEs are attached.  This
   interface may be a physical LAN interface or a VLAN.  The Provider
   Edge (PE) routers are MPLS Label Edge Routers (LERs) that serve as
   pseudowire endpoints.

      +----+                                              +----+
      + S1 +---+      ...........................     +---| S2 |
      +----+ | |      .                         .     |   +----+
       IPa   | |   +----+                    +----+   |    IPe
             + +---| PE1|---MPLS and/or IP---| PE2|---+
            / \    +----+         |Network   +----+   |
      +----+   +---+  .           |             .     |   +----+
      + S1 +   | S1|  .         +----+          .     +---| S2 |
      +----+   +---+  ..........| PE3|...........         +----+
       IPb       IPc            +----+                     IPf
                                  |
                                  |
                                +----+
                                | S3 |
                                +----+

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                                  IPd


   In the above diagram, an IPLS instance is shown with three sites:
   site S1, site S2 and site S3. In site S3, the CE device is directly
   connected to its PE.  In the other two sites, there are multiple CEs
   connected to a single PE. More precisely, the CEs at these sites are
   on an Ethernet (switched at site 1 and shared at site 2) network (or
   VLAN), and the PE is attached to that same Ethernet network or
   VLAN).  We impose the following restriction:  if one or more CEs
   attach to a PE by virtue of being on a common LAN or VLAN, there
   MUST NOT be more than one PE on that LAN or VLAN.

   PE1, PE2 and PE3 are shown as connected via an MPLS network;
   however, other tunneling technologies, such as GRE, L2TPv3, etc.,
   could also be used to carry the pseudowires.

   An IPLS instance is a single broadcast domain, such that each IP end
   station (e.g., IPa) appears to be co-located with other IP end
   stations (e.g., IPb through IPf) on the same subnet. The IPLS
   service is transparent to the CE devices and requires no changes to
   them.

4.0 Configuration

   Each PE router is configured with one or more IPLS service
   instances, and each IPLS service instance is associated with a
   unique VPN-Id. For a given IPLS service instance, a set of
   Attachment Circuits is identified. Each Attachment Circuit can be
   associated with only one IPLS instance. An Attachment Circuit, in
   this document, is either a customer-facing Ethernet port, or a
   particular VLAN (identified by an IEEE 802.1Q VLAN ID) on a
   customer-facing Ethernet port.

   The PE router can optionally be configured with a local MAC address
   to be used as source MAC address when IP packets are forwarded from
   a pseudowire to an Attachment Circuit. By default, a PE uses the MAC
   address of the customer-facing Ethernet interface for this purpose.

5.0 Discovery

   The discovery process includes:
     . Remote PE discovery
     . VPN (i.e., IPLS) membership discovery
     . IP CE end station discovery

   This draft does not discuss the remote PE discovery or VPN
   membership discovery. This information can either be user configured
   or can be obtained using auto-discovery techniques described in
   [BGP-Discovery] or other methods. However, the discovery of the CE
   is an important operational step in the IPLS model and is described
   below.

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5.1 CE discovery

   Each PE actively detects the presence of local CEs by snooping IP
   and ARP frames received over the Attachment Circuits. During the
   discovery phase, the PE examines each multicast/broadcast Ethernet
   frame. For link-local IP frames (for example IGP
   discovery/multicast/broadcast packets typically 224.0.0.x
   addresses), the CE's (source) MAC address is extracted from the
   Ethernet header and the (source) IP address is obtained from the IP
   header. For ARP frames, the source MAC and IP address are determined
   from the ARP PDU.

   For each CE, the PE maintains the following tuple: <Attachment
   Circuit identification info, VPN-Id, IP address, MAC address>.

   Once a CE is discovered, its status is monitored continuously by
   examining the received ARP frames and by periodically generating ARP
   requests. The absence of an ARP response from a CE after a
   configurable number of ARP requests is interpreted as loss of
   connectivity with the CE.

6.0 Pseudowire Creation

6.1 Receive Unicast Multipoint-to-point Pseudowire

   As the PE discovers each locally attached CE, a unicast multipoint-
   to-point pseudowire (mp2p PW) associated exclusively with that CE is
   created by distributing the CE's IP address and MAC address along
   with a PW-Label to all the remote PE peers that participate in the
   same IPLS instance. Note that the same value of a PW-label SHOULD be
   distributed to all the remote PE peers for a given CE. The mp2p PW
   thus created is used by remote PEs to send unicast IP traffic to a
   specific CE.

   (The same functionality can be provided by a set of point-to-point
   PWs, and the PE is not required to send the same PW-label to all the
   other PEs.  For convenience, however, we will use the term mp2p PWs,
   which may be implemented using a set of point-to-point PWs.)

   The PE forwards a frame received over this mp2p PW to the associated
   Attachment Circuit.

   The unicast pseudowire uses IP Layer2 Transport encapsulation as
   define in [PWE3-Control].

6.2 Receive Multicast Multipoint-to-point Pseudowire

   When a PE is configured to participate in an IPLS instance, it
   advertises a "multicast" PW-label to every other PE that is a member
   of the same IPLS. The advertised PW-label value is the same for each
   PE, which creates an mp2p pseudowire for IP multicast/broadcast
   traffic and ARP packets. There is only one multicast mp2p PW per PE

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   for each IPLS instance and this pseudowire is used exclusively to
   carry IP multicast/broadcast and ARP traffic from the remote PEs to
   this PE for this IPLS instance.

   Note that no special functionality is expected from this pseudowire.
   We call it a "multicast pseudowire" because we use it to carry
   multicast and broadcast IP and ARP traffic.  The pseudowire itself
   need not provide any different service than any of the unicast
   pseudowires.

   In particular, the Receive broadcast mp2p PW does not perform any
   replication of frames itself. Rather, it is there to signify to the
   PE that the PE needs to replicate a copy of a frame received over
   this mp2p PW onto all the attachment circuits that are associated
   with the IPLS instance of the mp2p PW.

   The multicast mp2p pseudowire is considered the principle pseudowire
   in the bundle of mp2p pseudowires that consist of one multicast mp2p
   pseudowire and a variable number of unicast mp2p pseudowires for a
   given IPLS instance. In a principle role, multicast PW represents
   the IPLS instance. The life of all unicast PWs in the IPLS instance
   depends on the existence of the multicast PW. If, for some reasons,
   multicast PW cease to exist, all the associated unicast pseudowires
   in the bundle are removed.

   The multicast pseudowire uses Ethernet encapsulation as defined in
   [PWE3-Ethernet].

   The use of pseudowires which are specially optimized for multicast
   is for further study.

6.3 Send Multicast Replication tree

   The PE creates a send replication tree for each IPLS instance, which
   consists of the collection of all attachment circuits and all the
   "multicast" pseudowires of the IPLS instance.

   Any ARP or multicast IP Ethernet frame received over an attachment
   circuit is replicated to the other attachment circuits and to the
   mp2p multicast pseudowire of the send replication tree. The send
   replication tree deals mostly with broadcast/multicast Ethernet MAC
   frames. One exception to this is unicast ARP frame, the processing
   of which is described in the following section.

   Any Ethernet frame received over the multicast PW is replicated to
   all the attachment circuits of the send replication tree of the IPLS
   instance associated with the incoming PW label. One exception is
   unicast ARP frame, the processing of which is described in the
   following section.

7.0 Signaling


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   [PWE3-CONTROL] uses the Label Distribution Protocol (LDP) to
   exchange PW-FECs in the Label Mapping message in a downstream
   unsolicited mode. The PW-FEC comes in two forms; PWid and
   Generalized PWid FEC elements. These FEC elements define some fields
   that are common between them. The discussions below refer to these
   common fields for IPLS related extensions. Note that the use of
   multipoint to point and unidirectional characteristics of the PW
   makes BGP as the ideal candidate for PW-FEC signaling. The use of
   BGP for such purposes is for future study.

7.1 IPLS PW Signaling

   An IPLS carries IP packets as payload over its unicast pseudowires
   and Ethernet packet as payload over its multicast pseudowire. The
   PW-type to be used for unicast pseudowire is the IP PW, defined in
   [PWE3-Control] as IP Layer2 Transport. The PW-type to be used for
   multicast pseudowire is the Ethernet PW as defined in [PWE3-ETH].

   When processing a received PW FEC, the PE matches the PW Id with the
   locally configured PW Id. If the PW type is Ethernet, the PW-FEC is
   for multicast PW. If the PW type is ôIP Layer2 transportö, the PW
   FEC is for unicast PW. For unicast PW, PE must check the presence of
   IP and MAC address parameters in the optional parameter fields of
   the Label Mapping message. If these parameters are absent, a Label
   Release message must be issued to reject the establishment of the
   unicast PW with the remote PE.

   The additional parameters for the unicast PW are defined as follows.

   Optional Parameter   type    length    value
   IP address           TBD      04       CEÆs IP address
   MAC Address          TBD      06       CEÆs MAC address

   The IP address field denotes the IP address of the advertising PE's
   attached CE device.

   The MAC address field denotes the MAC address of the advertising
   PE's attached CE device.


7.2 Signaling Advertisement Processing

   A PE should process a received [PWE3-CONTROL] advertisement with PW-
   type of IP Layer2 transport for IPLS as follows,
        - Verify the IPLS VPN membership by matching the VPN-Id
          signaled in the AGI field or the PW-ID field with all the
          VPN-Ids configured in the PE. Discard and release the PW
          label if VPN-Id is not found.
        - Program the Forwarding Information Base (FIB) such that when
          a unicast IP packet is received from an attachment circuit
          with its destination MAC address matching the advertised MAC
          address, the packet is forwarded out over the tunnel to the

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          advertising PE with the advertised PW-label as the inner
          label.

   A PE should process a received [PWE3-CONTROL] advertisement with the
   PW type of Ethernet for IPLS as follows,
        - Verify the IPLS VPN membership by matching the VPN-Id
          signaled in the AGI field or the PW-ID field with all the
          VPN-Ids configured in the PE. Discard and release the PW
          label if VPN-Id is not found.
        - Add the PW-label to the send broadcast replication tree for
          the VPN-Id. This enables sending a copy of a
          multicast/broadcast IP Ethernet frame or ARP Ethernet frame
          from the attachment circuit to this pseudowire.

8.0 Forwarding

8.1 Non-IP or non-ARP traffic

   In an IPLS VPN, a PE forwards only IP and ARP traffic. All other
   frames are dropped silently.  If the CEs must pass non-IP traffic to
   each other, they must do so through IP tunnels that terminate at the
   CEs themselves.

8.2 Unicast IP Traffic

   In IPLS, IP traffic is forwarded from the Attachment Circuit to the
   PW based on the destination MAC address of the layer 2 frame (and
   not based on the IP Header).

   The PE identifies the FIB associated with an IPLS instance based on
   the Attachment Circuit or the PW label. When a frame is received
   from an Attachment Circuit, the PE uses the destination MAC address
   as the lookup key. When a frame is received from a PW, the PE uses
   the PW-Label as the lookup key. The frame is dropped if the lookup
   fails.

8.3 Broadcasts and Multicast IP Traffic

   When the destination MAC address is either a broadcast or multicast,
   a copy of the frame is sent to the control plane for CE discovery
   purposes (see section 5.1).It is important to note that the frames
   sent to the control plane is applied stricter rate limiting criteria
   to avoid overwhelming the control plane under adverse conditions
   such as Denial Of Service attack. The service provider should also
   provide a configurable limitation to prevent overflowing of the
   learned source addresses in a given IPLS instance. Also, a caution
   must be used such that only link local multicasts and broadcast IP
   packets are sent to control plane.

   When a multicast/broadcast IP packet is received from an Attachment
   Circuit, the PE replicates it onto the Send Multicast Replication
   Tree (See section 6.3). When a multicast/broadcast IP Ethernet frame
   is received from a pseudowire, the PE forwards a copy of the frame

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   to all attachment circuits associated with the IPLS VPN instance
   involved. Note that multicast PW uses Ethernet encapsulation and
   hence does not require additional header manipulations.

8.4 ARP Traffic

   When a broadcast ARP frame is received over the attachment circuit,
   a copy of the frame is sent to the control plane for CE discovery
   purposes. The PE replicates the frame onto the Send Multicast
   Replication Tree (see section 6.3), which results into a copy to be
   delivered to all the remote PEs on the broadcast PW and other local
   CEs through the egress attachment circuits.

   When a broadcast ARP frame is received over the broadcast PW, a copy
   of the Ethernet ARP frame is sent to all the attachment circuits
   associated with the IPLS instance.

   When a unicast ARP Ethernet frame is received over the attachment
   circuit, a copy of the frame is sent to the control plane for the CE
   discovery purposes. The PE may optionally do MAC DA lookup in the
   forwarding table and send the ARP frame to a specific egress
   interface (attachment circuit or broadcast PW to a remote PE) or
   replicate the frame onto the Send Multicast Replication Tree (see
   section 6.3).

   When a unicast ARP Ethernet frame is received over the broadcast PW,
   PE may optionally do MAC DA lookup in the forwarding table and
   forward it to an attachment circuit where the CE is located. If the
   CE is not accessible through any local attachment circuit, the frame
   is dropped. Conversely, the PE may simply forward the frame to all
   the attachment circuits associated with that IPLS instance without
   any lookup in the forwarding table.

8.5 Encapsulation

   The Ethernet MAC header of a unicast IP packet received from an
   Attachment Circuit is stripped before forwarding the frame to the
   unicast pseudowire. However, the MAC header is retained for the
   following cases,
     . when a frame is unicast or broadcast IP packet that is directed
        to one or more local Attachment Circuit(s).
     . when a frame is a broadcast IP packet
     . when a frame is an ARP packet

   An IP frame received over a unicast pseudowire is prepended with a
   MAC header before transmitting it on the appropriate Attachment
   Circuit(s). The fields in the MAC header are filled in as follows:
        - The destination MAC address is the MAC address associated
          with the PW label in the FIB
        - The source MAC address is the PE's own local MAC address or a
          MAC address which has been specially configured on the PE for
          this use.
        - The Ethernet Type field is 0x0800

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        - The frame may be IEEE802.1Q tagged based on the VLAN
          information associated with the Attachment Circuit.

   An FCS is appended to the frame.

9.0   Attaching to IPLS via ATM or FR

   In addition to (i) an Ethernet port and a (ii) combination of
   Ethernet port and a VLAN ID, an Attachment Circuit to IPLS may also
   be (iii) an ATM or FR VC carrying encapsulated bridged Ethernet
   frames or (iv) the combination of an ATM or FR VC and a VLAN ID.

   The ATM/FR VC is just used as a way to transport Ethernet frames
   between a customer site and the PE. The PE terminates the ATM/FR VC
   and operates on the encapsulated Ethernet frames exactly as if those
   were received on a local Ethernet interface. When a frame is
   propagated from pseudowire to a ATM or FR VC the PE prepends the
   Ethernet frame with the appropriate bridged encapsulation header as
   defined in [RFC 2684] and [RFC 2427] respectively. Operation of an
   IPLS over ATM/FR VC is exactly as described above, with the
   exception that the attachment circuit is then identified via the ATM
   VCI/VPI or Frame Relay DLCI (instead of via a local Ethernet port
   ID), or a combination of those with a VLAN ID.

10.0 VPLS vs IPLS

   The VPLS approach proposed in [VPLS] provides VPN services for IP as
   well as other protocols. The IPLS approach described in this draft
   is similar to VPLS in many respects:
        - It provides a Provider Provisioned Virtual LAN service with
          multipoint capability where a CE connected via a single
          attachment circuit can reach many remote CEs
        - It appears as a broadcast domain and a single subnet
        - forwarding is based on destination MAC addresses

   However, unlike VPLS, IPLS is restricted to IP traffic only. By
   restricting the scope of the service to the predominant type of
   traffic in today's environment, IPLS eliminates the need for service
   provider edge routers to implement some bridging functions such as
   MAC address learning in the data path (by, instead, distributing MAC
   information in the control plane). Thus this solution offers a
   number of benefits:

        - Facilitates Virtual LAN services in instances where PE
          devices cannot or cannot efficiently (or are specifically
          configured not to) perform MAC address learning.
        - Unknown Unicast frames are never flooded as would be the case
          in VPLS.
        - Encapsulation is more efficient (MAC header is stripped) for
          unicast IP packets while traversing the backbone network.
        - PE devices are not burdened with the processing overhead
          associated with traditional bridging (e.g., STP processing,
          etc.). Note however that some of these overheads (e.g., STP

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          processing) could optionally be turned-off with a VPLS
          solution in the case where it is known that only IP devices
          are interconnected.
        - Loops (perhaps through backdoor links) are minimized since a
          PE could easily reject (via label release) a duplicate IP to
          MAC address advertisement.

11.0 IP Protocols

   The solution described in this document offers IPLS service for IPv4
   traffic only. For this reason, the MAC Header is not carried over
   the unicast pseudowire. It is reconstructed by the PE when receiving
   a packet from a unicast pseudowire and the Ethertype 0x0800 is used
   in the MAC Header since IPv4 is assumed.

   However, this solution may be extended to carry other types of
   important traffic such as ISIS and IPv6 which are not encapsulated
   in Ethernet with the use of Ethertype 0x0800. In order to permit the
   propagation of such packets correctly, one may create a separate set
   of pseudowires, or pass protocol information in the "control word"
   of a "multiprotocol" pseudowire, or encapsulate the Ethernet MAC
   Header in the pseudowire. The selection of appropriate
   multiplexing/demultiplexing scheme is the subject of future study.
   The current document focuses on IPLS service for IPv4 traffic.

12.0 Dual Homing with IPLS

   As stated in previous sections, IPLS prohibits connection of a
   common LAN or VLAN to more than one PE. Alternatively the CE device
   itself can connect to more than one instance of IPLS through two
   separate LAN or VLAN connections to separate PEs. To the CE IP
   device, these separate connections appear as connections to two IP
   subnets. The failure of reachability through one subnet is then
   resolved via the other subnet using IP routing protocols.


13.0 Acknowledgements

   Authors would like to thank L2VPN working group members for their
   valuable comments.


14.0 Security Considerations

   The security aspects of this solution will be discussed at a later
   time.


15.0 References

15.1 Normative References



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   [ARP] RFC 826, STD 37, D. Plummer, "An Ethernet Address Resolution
   Protocol:  Or Converting Network Protocol Addresses to 48.bit
   Ethernet Addresses for Transmission on Ethernet Hardware".

   [INVARP] RFC 2390, T. Bradley et al., "Inverse Address Resolution
   Protocol".

   [PWE3-Control] L. Martini et al., "Pseudowire Setup and Maintenance
   using LDP", February 2005, work in progress.


   [PWE3-IANA] L. Martini et al,. ôIANA Allocations for pseudo Wire
   Edge to Edge Emulation (PWE3)ö, February 2005, work in progress.

   [VPLS] Lasserre et al, "Virtual Private LAN Service over MPLS",
   draft-ietf-l2vpn-vpls-ldp-06.txt, August 2005 (work in progress).

15.2 Informative References

   [L2VPN-FRM] L. Andersson et al., "Framework for L2VPN", December
   2004, work in progress.


   [PROXY-ARP] RFC 925, J. Postel, "Multi-LAN Address Resolution".


   [L2VPN-REQ] Augustyn, W. et.al "Service Requirements for Layer 2
   Provider Provisioned Virtual Private Networks", draft-ietf-l2vpn-
   requirements-04.txt, Work in Progress, Internet Draft, August 2005.

   [BGP-Discovery] "Using BGP as an Auto-Discovery Mechanism for
   Provider Provisioned VPNs", Ould-Brahim et al., draft-ietf-l3vpn-
   bgpvpn-auto-04.txt, May 2004, (work in progress).

   [RFC-1112] Deering, S., "Host Extensions for IP Multicasting", RFC
   1112, August, 1989.

16.0 Author's Address

   Himanshu Shah
   Ciena Networks
   35 Nagog Park,
   Acton, MA 01720
   Email: hshah@ciena.com

   K.Arvind
   Enterasys Networks
   50 Minuteman Rd, Suite 100
   Andover, MA 01810
   Email: karvind@enterasys.com

   Eric Rosen
   Cisco Systems

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   300 Apollo Drive,
   Chelmsford, MA 01824
   Email: erosen@cisco.com

   Giles Heron
   Tellabs
   Abbey Place
   24-28 Easton Street
   High Wycombe
   Bucks
   HP11 1NT
   UK
   Email: giles.heron@tellabs.com

   Francois Le Faucheur
   Cisco Systems, Inc.
   Village d'Entreprise Green Side - Batiment T3
   400, Avenue de Roumanille
   06410 Biot-Sophia Antipolis, France
   Email: flefauch@cisco.com

   Vasile Radoaca
   Email: vasile@westridgenetworks.com

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