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VPLS PE Model for E-Tree Support
draft-ietf-l2vpn-vpls-pe-etree-00

The information below is for an old version of the document.
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This is an older version of an Internet-Draft that was ultimately published as RFC 7796.
Authors Yuanlong Jiang , Lucy Yong , Manuel Paul , Frederic JOUNAY , Florin Balus , Wim Henderickx , Ali Sajassi
Last updated 2012-09-12
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draft-ietf-l2vpn-vpls-pe-etree-00
Internet Working Group                                        Y. Jiang
                                                               L. Yong
Internet Draft                                                  Huawei

Intended status: Standards Track                               M. Paul
                                                      Deutsche Telekom

                                                             F. Jounay
                                                             Orange CH

                                                              F. Balus
                                                         W. Henderickx
                                                        Alcatel-Lucent

                                                            A. Sajassi
                                                                 Cisco

Expires: March 2013                                 September 12, 2012

                      VPLS PE Model for E-Tree Support
                   draft-ietf-l2vpn-vpls-pe-etree-00.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on March 12, 2013.

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Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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.

Abstract

   A generic VPLS solution for E-Tree services is proposed which uses
   VLANs to indicate root/leaf traffic. A VPLS Provider Edge (PE) model
   is illustrated as an example for the solution. In the solution, E-
   Tree VPLS PEs are interconnected by PWs which carry the VLAN
   indicating the E-Tree attribute, the MAC address based Ethernet
   forwarding engine and the PW work in the same way as before. A
   signaling mechanism for E-Tree capability and VLAN mapping
   negotiation is further described.

Table of Contents

   1.   Introduction ............................................. 3
   2.   Conventions used in this document ........................ 4
   3.   Terminology .............................................. 4
   4.   PE Model with E-Tree Support ............................. 5
      4.1. Existing PE Models .................................... 5
      4.2. A New PE Model with E-Tree Support .................... 8
   5.   PW for E-Tree Support .................................... 9
      5.1. PW Encapsulation ...................................... 9
      5.2. VLAN Mapping .......................................... 9
      5.3. PW Processing ........................................ 11
         5.3.1.  PW Processing in the VLAN Mapping Mode ......... 11
         5.3.2.  PW Processing in the Compatible Mode ........... 12
         5.3.3.  PW Processing in the Optimized Mode ............ 13
   6.   LDP Extensions for E-Tree Support ....................... 14
   7.   BGP Extensions for E-Tree Support ....................... 16
   8.   OAM Considerations ...................................... 17
   9.   Applicability ........................................... 18
   10.  Security Considerations ................................. 18
   11.  IANA Considerations ..................................... 18

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   12.  References .............................................. 19
      12.1.   Normative References .............................. 19
      12.2.   Informative References ............................ 19
   13.  Acknowledgments ......................................... 20
   Appendix A. Other PE Models for E-Tree ....................... 21
      A.1. A PE Model With a VSI and No bridge .................. 21
      A.2. A PE Model With external E-Tree interface ............ 22

1. Introduction

   The E-Tree service is defined in Metro Ethernet Forum (MEF) as a
   Rooted-Multipoint EVC service. It is a multipoint Ethernet service
   with special restrictions: the frames from a root may be received by
   any other root or leaf, and the frames from a leaf may be received by
   any root, but MUST not be received by a leaf. Further, an E-Tree
   service may include multiple roots and multiple leaves. Although VPMS
   or P2MP multicast is a somewhat simplified version of this service,
   in fact, there is no exact corresponding terminology in IETF.

   [Etree-req] gives the requirements for providing E-Tree solutions in
   the VPLS and the need to filter leaf-to-leaf traffic.

   [Vpls-etree] describes a PW control word based E-Tree solution, where
   a bit in the PW control word is used to indicate the root/leaf
   attribute for a packet. The Ethernet forwarder in the VPLS is also
   extended to filter the leaf-to-leaf traffic based on the <ingress
   port, egress port, CW L-bit> tuple.

   [Etree-2PW] proposes another E-Tree solution where root and leaf
   traffic are classified and forwarded in the same VSI but with two
   separate PWs.

   Both solutions are only applicable to "VPLS only" networks.

   In fact, VPLS PE usually consists of a bridge module itself (see
   [RFC4664] and [RFC6246]); moreover, E-Tree services may cross both
   Ethernet and VPLS domains. Therefore, it is necessary to develop an
   E-Tree solution both for "VPLS only" scenarios and for interworking
   between Ethernet and VPLS.

   IEEE 802.1 has incorporated the generic E-Tree solution in the latest
   version of 802.1Q [802.1aq], which is just an improvement on the
   traditional asymmetric VLAN mechanism (the use of different VLANs to
   indicate E-Tree root/leaf attributes and prohibiting leaf-to-leaf
   traffic with the help of VLANs was first standardized in IEEE 802.1Q-

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   2003). In the solution, VLANs are used to indicate root/leaf
   attribute of a packet: one VLAN ID is used to indicate the frames
   originated from the roots and another VLAN ID is used to indicate the
   frames originated from the leaves. At a leaf port, the bridge can
   then filter out all the frames from other leaf ports based on the
   VLAN ID. It is better to reuse the same mechanism in VPLS than to
   develop a new mechanism. The latter will introduce more complexity to
   interwork with IEEE 802.1Q solution.

   This document introduces how the Ethernet VLAN solution can be used
   to support generic E-Tree services in the VPLS. The solution proposed
   here is fully compatible with the IEEE bridge architecture and the
   IETF PWE3 technology, thus it will not change the FIB (such as
   installing E-Tree attributes in the FIB), or need any specially
   tailored implementation. Furthermore, VPLS scalability and simplicity
   is also well kept. With this mechanism, it is also convenient to
   deploy a converged E-Tree service across both Ethernet and MPLS
   networks.

   Firstly, a typical VPLS PE model is introduced as an example; the
   model is then extended in which a Tree VSI is connected to a VLAN
   bridge with a dual-VLAN interface.

   This document then discusses the PW encapsulation and PW processing
   such as VLAN mapping options for transporting E-Tree services in a
   VPLS.

   Finally, it describes the signaling extensions for E-Tree support and
   PE processing procedures.

2. 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].

3. Terminology

   E-Tree: a Rooted-Multipoint EVC service as defined in MEF 6.1

   EVC: Ethernet Virtual Connection, as defined in MEF 4.0

   FIB: Forwarding Information Base, or forwarding table

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   T-VSI: Tree VSI, a VSI with E-Tree support

   Root AC, an AC attached with a root

   Leaf AC, an AC attached with a leaf

   C-VLAN, Customer VLAN

   S-VLAN, Service VLAN

   B-VLAN, Backbone VLAN

   Root VLAN, a VLAN ID used to indicate all the frames that are
   originated at a root AC

   Leaf VLAN, a VLAN ID used to indicate all the frames that are
   originated at a leaf AC

   I-SID, Backbone Service Instance Identifier, as defined in IEEE
   802.1ah

4. PE Model with E-Tree Support

   "VPLS only" PE architecture as shown in Fig. 1 of [Etree-req] is a
   simplification of the VPLS and PWE3 architecture, several common VPLS
   PE architectures are discussed in more details in [RFC4664] and
   [RFC6246].

   Therefore, VLAN based E-Tree solution are demonstrated with the help
   of a typical VPLS PE model. It can also be used by other PE models
   which are discussed in Appendix A.

4.1. Existing PE Models

   According to [RFC4664], there are at least three models possible for
   a VPLS PE, including:

   o A single bridge module, a single VSI;

   o A single bridge module, multiple VSIs;

   o Multiple bridge modules, each attaches to a VSI.

   The second PE model is commonly used. A typical example is further
   depicted in Fig. 1 and Fig. 2 [RFC6246], where an S-VLAN bridge
   module is connected to multiple VSIs each with a single VLAN virtual
   interface.

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                      +-------------------------------+
                      |  802.1ad Bridge Module Model  |
                      |                               |
           +---+      |  +------+      +-----------+  |
           |CE |---------|C-VLAN|------|           |  |
           +---+      |  |bridge|------|           |  |
                      |  +------+      |           |  |
                      |     o          |   S-VLAN  |  |
                      |     o          |           |  |
                      |     o          |   Bridge  |  |
           +---+      |  +------+      |           |  |
           |CE |---------|C-VLAN|------|           |  |
           +---+      |  |bridge|------|           |  |
                      |  +------+      +-----------+  |
                      +-------------------------------+

                 Figure 1  A model of 802.1ad Bridge Module

           +----------------------------------------+
           |           VPLS-capable PE model        |
           |   +---------------+          +------+  |
           |   |               |          |VSI-1 |------------
           |   |               |==========|      |------------ PWs
           |   |     Bridge    ------------      |------------
           |   |               | S-VLAN-1 +------+  |
           |   |     Module    |             o      |
           |   |               |             o      |
           |   |   (802.1ad    |             o      |
           |   |    bridge)    |             o      |
           |   |               |             o      |
           |   |               | S-VLAN-n +------+  |
           |   |               ------------VSI-n |-------------
           |   |               |==========|      |------------- PWs
           |   |               |     ^    |      |-------------
           |   +---------------+     |    +------+  |
           |                         |              |
           +-------------------------|--------------+
                            LAN emulation Interface

                     Figure 2  A VPLS-capable PE Model

   In this PE model, Ethernet frames from Customer Edges (CEs) will
   cross multiple stages of bridge modules (i.e., C-VLAN and S-VLAN
   bridge) and a VSI in a PE before being sent on the PW to a remote PE.
   Therefore, the association between an AC port and a PW on a VSI as

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   required in [Vpls-etree] or [Etree-2PW] is difficult, sometimes even
   impossible.

   This model could be further enhanced: When Ethernet frames arrive at
   a PE, a root VLAN or a leaf VLAN tag is added. Then the frames with
   the root VLAN tag are transmitted both to the roots and the leaves,
   while the frames with the leaf VLAN tag are transmitted to the roots
   but dropped for the leaves (these VLAN tags are removed before the
   frames are transmitted over the wire). It was demonstrated in
   [802.1aq] that the E-Tree service in Ethernet networks can be well
   supported with this mechanism.

   Assuming this mechanism is implemented in the bridge module, it is
   quite straightforward to infer a VPLS PE model with two VSIs to
   support the E-Tree (as shown in Fig. 3). But this model will require
   two VSIs per PE and two sets of PWs per E-Tree service, which is
   poorly scalable in a large MPLS/VPLS network; in addition, both these
   VSIs have to share their learned MAC addresses.

           +----------------------------------------+
           |           VPLS-capable PE model        |
           |   +---------------+          +------+  |
           |   |               |          |VSI-1 |------------
           |   |               |==========|      |------------ PWs
           |   |     Bridge    ------------      |------------
           |   |               | Root     +------+  |
           |   |     Module    | S-VLAN             |
           |   |               |                    |
           |   |   (802.1ad    |                    |
           |   |    bridge)    |                    |
           |   |               | Leaf               |
           |   |               | S-VLAN   +------+  |
           |   |               ------------VSI-2 |-------------
           |   |               |==========|      |------------- PWs
           |   |               |     ^    |      |-------------
           |   +---------------+     |    +------+  |
           |                         |              |
           +-------------------------|--------------+
                            LAN emulation Interface

              Figure 3  A VPLS PE Model for E-Tree with 2 VSIs

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4.2. A New PE Model with E-Tree Support

   In order to support the E-Tree in a more scalable way, a new VPLS PE
   model with a single Tree VSI (T-VSI, a VSI with E-Tree support) is
   proposed. As depicted in Fig. 4, the bridge module is connected to
   the T-VSI with a dual-VLAN virtual interface, i.e., both the root
   VLAN and the leaf VLAN are connected to the same T-VSI, and they
   share the same FIB and work in shared VLAN learning. In this way,
   only one VPLS instance and one set of PWs is needed per E-Tree
   service, and the scalability of VPLS is improved.

           +----------------------------------------+
           |           VPLS-capable PE model        |
           |   +---------------+          +------+  |
           |   |               |==========|TVSI-1|------------
   +---+AC |   |               ------------      |------------ PWs
   |CE |-------|     Bridge    ------------      |------------
   +---+   |   |               | Root &   +------+  |
           |   |     Module    | Leaf VLAN   o      |
           |   |               |             o      |
           |   |               |             o      |
           |   |               |             o      |
           |   |               |             o      |
   +---+AC |   |               |   VLAN-n +------+  |
   |CE |-------|               ------------VSI-n |-------------
   +---+   |   |               |==========|      |------------- PWs
           |   |               |     ^    |      |-------------
           |   +---------------+     |    +------+  |
           |                         |              |
           +-------------------------|--------------+
                            LAN emulation Interface

          Figure 4  A VPLS PE Model for E-Tree with a Single T-VSI

   For an untagged port (customer sites attached to the PEs with
   untagged ports), the Ethernet frames received from the root ACs can
   be tagged with a root C-VLAN, and optionally be added with another
   root S-VLAN. Alternatively, the frames from the root ACs can be
   tagged with the root S-VLAN tag directly in the VPLS network domain.

   For a C-VLAN tagged port, the Ethernet frames received from the root
   ACs can be added with a root S-VLAN. Alternatively, the C-VLAN can be
   translated to the root S-VLAN in the VPLS network domain.

   For an S-VLAN tagged port, the S-VLAN tag in the Ethernet frames
   received from the root ACs can be translated to the root S-VLAN in
   the VPLS network domain. Alternatively, the PBB VPLS PE model (where

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   an IEEE 802.1ah bridge module is embedded in the PE) as described in
   [PBB-VPLS] can be used, and a root B-VLAN or leaf B-VLAN can be added
   in this case (the E-Tree attribute may also be indicated with two I-
   SID tags in the bridge module, and the frames are further
   encapsulated and transported transparently over a single B-VLAN, thus
   the PBB VPLS works just in the same way as described in [PBB-VPLS]
   and will be discussed no more in this document). When many S-VLANs
   are multiplexed in a single AC, the 2nd option has an advantage of
   both VLAN scalability and MAC address scalability.

   In a similar way, the traffic from the leaf ACs is tagged and
   transported on the leaf C-VLAN, S-VLAN or B-VLAN.

   In all cases, the outermost VLAN in the resulted Ethernet header is
   used to indicate the E-Tree attribute of an Ethernet frame; this
   document will use VLAN to refer to this outermost VLAN for simplicity
   in the latter sections.

5. PW for E-Tree Support

5.1. PW Encapsulation

   To support an E-Tree service, T-VSIs in a VPLS must be interconnected
   with a bidirectional Ethernet PW. The Ethernet PW may work in the
   tagged mode (PW type 0x0004) as described in [RFC4448], and a VLAN
   tag must be carried in each frame in the PW to indicate the frame
   originated from either root or leaf (the VLAN tag indicating the
   frame originated from either root or leaf can be translated by a
   bridge module in the PE or added by an outside Ethernet edge device,
   even by a customer device). In the tagged PW mode, two service
   delimiting VLANs must be allocated in the VPLS domain for an E-Tree.
   PW processing for the tagged PW will be described in Section 5.3 of
   this document.

   Raw PW (PW type 0x0005 in [RFC4448]) may be used to carry E-Tree
   service for a PW in Compatible mode as shown in Section 5.3.2.

5.2. VLAN Mapping

   There are two ways of manipulating VLANs for an E-Tree in VPLS:

   o Global VLAN based, that is, provisioning two global VLANs (Root
      VLAN, Leaf VLAN) across the VPLS network, thus no VLAN mapping is
      needed at all, or the VLAN mapping is done completely in the
      Ethernet domains.

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   o Local VLAN based, that is, provisioning two local VLANs for each
      PE (which participates in the E-Tree) in the VPLS network
      independently.

   The first method requires no VLAN mapping in the PW, but two unique
   service delimiting VLANs must be allocated across the VPLS domain.

   The second method is more scalable in the use of VLANs, but needs a
   VLAN mapping mechanism in the PW similar to what is already described
   in Section 4.3 of [RFC4448].

   Global or local VLANs can be manually configured or provisioned by an
   OSS system. Alternatively, some automatic VLAN allocation algorithm
   may be provided in the management plane, but it is out scope of this
   document.

   For both methods, VLAN mapping parameters from a remote PE can be
   provisioned or determined by a signaling protocol as described in
   Section 6 when a PW is being established.

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5.3. PW Processing

5.3.1.PW Processing in the VLAN Mapping Mode

   In the VLAN Mapping mode, two VPLS PEs with E-Tree capability are
   inter-connected with a PW (For example, the scenario of Fig. 5
   depicts the interconnection of two PEs miscellaneously attached with
   both root and leaf nodes).

                  +------------------------+
                  |  VPLS PE with T-VSI    |
                  |                        |
        +----+    | +------+       +-----+ |  PW
        |Root|------| VLAN |-------|T-VSI|----------
        +----+    | | BRG  |       |     |----------
        +----+    | |      |-------|     |----------
        |Leaf|------|      |       |     |---------+
        +----+    | +------+       +-----+ |       |
                  |                        |       |
                  +------------------------+       |
                                                   |
                  +------------------------+       |
                  |  VPLS PE with T-VSI    |       |
                  |                        |       |
        +----+    | +------+       +-----+ |  PW   |
        |Root|------| VLAN |-------|T-VSI|---------+
        +----+    | | BRG  |       |     |----------
        +----+    | |      |-------|     |----------
        |Leaf|------|      |       |     |----------
        +----+    | +------+       +-----+ |
                  |                        |
                  +------------------------+

              Figure 5 T-VSI Interconnected in the Normal Mode

   If a PE is in the VLAN mapping mode for a PW, then in the data plane
   the PE MUST map the VLAN in each frame as follows:

    o Upon transmitting frames on the PW, map from local VLAN to remote
    VLAN (i.e., the local leaf VLAN in a frame is translated to the
    remote leaf VLAN; the local root VLAN in a frame is translated to the
    remote root VLAN).

    o Upon receiving frames on the PW, map from remote VLAN to local VLAN,
    and the frames are further forwarded or dropped in the egress bridge
    module using the filtering mechanism as described in [802.1aq].

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5.3.2.PW Processing in the Compatible Mode

   The new VPLS PE model can work in a traditional VPLS network
   seamlessly in the compatibility mode. As shown in Fig. 6, the VPLS PE
   with T-VSI can be attached with root and/or leaf nodes, while the
   VPLS PE with a traditional VSI can only be attached with root nodes.
   Raw PW should be used to connect with a traditional PE.

                  +------------------------+
                  |  VPLS PE with T-VSI    |
                  |                        |
        +----+    | +------+       +-----+ |  PW
        |Root|------| VLAN |-------|T-VSI|----------
        +----+    | | BRG  |       |     |----------
        +----+    | |      |-------|     |----------
        |Leaf|------|      |       |     |---------+
        +----+    | +------+       +-----+ |       |
                  |                        |       |
                  +------------------------+       |
                                                   |
                  +------------------------+       |
                  |  VPLS PE with VSI      |       |
                  |                        |       |
        +----+    | +------+       +-----+ |  PW   |
        |Root|------| VLAN |-------|VSI  |---------+
        +----+    | | BRG  |       |     |----------
        +----+    | |      |       |     |----------
        |Root|------|      |       |     |----------
        +----+    | +------+       +-----+ |
                  |                        |
                  +------------------------+

             Figure 6 T-VSI interconnected with Traditional VSI

   If a PE is in the Compatible mode for a PW, then in the data plane
   the PE MUST process the frame as follows:

    o Upon transmitting frames on the PW, remove the root or leaf VLAN in
    the frames.

    o Upon receiving frames on the PW, add a VLAN tag with a value of the
    local root VLAN to the frames.

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5.3.3.PW Processing in the Optimized Mode

   When two PEs are connected with their T-VSIs and one PE (e.g., PE2)
   is attached with only leaf nodes, as shown in the scenario of Fig. 6,
   the peer PE (e.g., PE1) should then work in the optimization mode. In
   this case, PE1 should not send the frames originated from the local
   leaf VLAN to PE2, i.e., these frames are dropped rather than
   transported over the PW. The bandwidth efficiency of the VPLS can
   thus be improved. The signaling for the PE attached with only leaf
   nodes is specified in Section 6.
                  +------------------------+
                  |VPLS PE with T-VSI (PE1)|
                  |                        |
        +----+    | +------+       +-----+ |  PW
        |Root|------| VLAN |-------|T-VSI|----------
        +----+    | | BRG  |       |     |----------
        +----+    | |      |-------|     |----------
        |Leaf|------|      |       |     |---------+
        +----+    | +------+       +-----+ |       |
                  |                        |       |
                  +------------------------+       |
                                                   |
                  +------------------------+       |
                  |VPLS PE with T-VSI (PE2)|       |
                  |                        |       |
        +----+    | +------+       +-----+ |  PW   |
        |Leaf|------| VLAN |-------|T-VSI|---------+
        +----+    | | BRG  |       |     |----------
        +----+    | |      |-------|     |----------
        |Leaf|------|      |       |     |----------
        +----+    | +------+       +-----+ |
                  |                        |
                  +------------------------+

     Figure 7 T-VSI interconnected with PE attached with only leaf nodes

   If a PE is in the Optimized Mode for a PW, upon transmit, the PE
   SHOULD first operate as follows:

   o Drop a frame if its VLAN ID matches the local leaf VLAN ID.

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6. LDP Extensions for E-Tree Support

   In addition to the signaling procedures as specified in [RFC4447],
   this document proposes a new interface parameter sub-TLV to provision
   an E-Tree service and negotiate the VLAN mapping function, 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  E-Tree       |   Length=8    |           Reserved        |P|V|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Root VLAN ID         |          Leaf VLAN ID         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          Figure 8  E-Tree Sub-TLV

   Where:

   o E-Tree is the sub-TLV identifier to be assigned by IANA.

   o Length is the length of the sub TLV in octets.

   o Reserved bits MUST be set to zero on transmit and be ignored on
      receive.

   o P is a Leaf-only bit, it is set to 1 to indicate that the PE is
      attached with only leaf nodes, and set to 0 otherwise.

   o V is a bit indicating the sender's VLAN mapping capability. A PE
      capable of VLAN mapping MUST set this bit, and clear it otherwise.

   o Root VLAN ID is the value of the local root VLAN.

   o Leaf VLAN ID is the value of the local leaf VLAN.

   When setting up a PW for the E-Tree based VPLS, two PEs negotiate the
   E-Tree support using the above E-Tree sub-TLV. Note PW type of 0x0004
   should be used during the PW negotiation.

   A PE that wishes to support E-Tree service MUST include an E-Tree
   Sub-TLV in its PW label mapping message and include its local root
   VLAN ID and leaf VLAN ID in the TLV.  A PE that has the VLAN mapping
   capability MUST set the V bit to 1, and a PE is attached with only
   leaf nodes SHOULD set the P bit to 1.

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   In default, for each PW, VLAN-Mapping-Mode, Compatible-Mode, and
   Optimized-Mode are all set to FALSE.

   A PE that receives a PW label mapping message with an E-Tree Sub-TLV
   from its peer PE must process it as follows:

   1) if the root and leaf VLAN ID in the message match the local root
      and leaf VLAN ID, then continue to 3);

   2) else {

          if the bit V is cleared, then {

                if the PE is capable of VLAN mapping, then it MUST set
                VLAN-Mapping-Mode to TRUE;

                else {

                     A label release message with the error code "E-Tree
                     VLAN mapping not supported" is sent to the peer PE
                     and exit the process;

                     }

          }

          if the bit V is set, and the PE is capable of VLAN mapping,
          then the PE with the minimum IP address MUST set VLAN-Mapping-
          Mode to TRUE;

      }

   3) If the P bit is set, then:

      {

          If the PE is a leaf-only node itself, then a label release
      message with a status code "Leaf to Leaf PW released" is sent to
      the peer PE and exit the process;

          Else the PE SHOULD set the Optimized-Mode to TRUE.

      }

   If a PE has sent an E-Tree Sub-TLV but does not receive any E-Tree
   Sub-TLV in its peer's PW label mapping message, The PE SHOULD then

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   establish a raw PW with this peer as in traditional VPLS and set
   Compatible-Mode to TRUE for this PW.

   Data plane processing for this PW is as following:

   If Optimized-Mode is TRUE, then data plane processing as described in
   Section 5.3.3 applies.

   If VLAN-Mapping-Mode is TRUE, then data plane processing  as
   described in Section 5.3.1 applies.

   If Compatible-Mode is TRUE, then data plane processing is as
   described in Section 5.3.2.

   PW processing as described in [RFC4448] proceeds as usual for all
   cases.

7. BGP Extensions for E-Tree Support

   A new E-Tree extended community is proposed for E-Tree signaling in
   BGP VPLS:

                   +------------------------------------+
                   | Extended community type (2 octets) |
                   +------------------------------------+
                   |  Root VLAN (2 octets)              |
                   +------------------------------------+
                   |  Leaf VLAN (2 octets)              |
                   +------------------------------------+
                   |  Reserved                        |P|
                   +------------------------------------+

                     Figure 9 E-Tree Extended Community

   Where:

   o Root VLAN ID is the value of the local root VLAN.

   o Leaf VLAN ID is the value of the local leaf VLAN.

   o Reserved, 15 bits MUST be set to zero on transmit and be ignored
      on receive.

   o P is a Leaf-only bit, it is set to 1 to indicate that the PE is
      attached with only leaf nodes, and set to 0 otherwise.

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   The PEs attached with both leaf and root nodes must support BGP E-
   Tree signaling as described in this document, and must support VLAN
   mapping in their data planes. The traditional PE attached with only
   root nodes may also participate in an E-Tree service.

   In BGP VPLS signaling, besides attaching a Layer2 Info Extended
   Community as detailed in [RFC4761], an E-Tree Extended Community MUST
   be further attached if a PE wishes to participate in an E-Tree
   service. The PE MUST include its local root VLAN ID and leaf VLAN ID
   in the E-Tree Extended Community. A PE attached with only leaf nodes
   of an E-Tree SHOULD set the P bit in the E-Tree Extended Community to
   1.

   A PE that receives a BGP UPDATE message with an E-Tree Extended
   Community from its peer PE must process it as follows (after
   processing procedures as specified in Section 3.2 of [RFC4761]):

   1) if the root and leaf VLAN ID in the E-Tree Extended Community
      match the local root and leaf VLAN ID, then continue to 3);

   2) else {

          the PE with the minimum IP address MUST set VLAN-Mapping-Mode
          to TRUE;

      }

   3) If the P bit is set, then the PE SHOULD set the Optimized-Mode to
      TRUE.

   A PE which does not recognize this attribute shall ignore it silently.
   If a PE has sent an E-Tree Extended Community but does not receive
   any E-Tree Extended Community from its peer, the PE SHOULD then
   establish a raw PW with this peer as in traditional VPLS, and set
   Compatible-Mode to TRUE for this PW.

   Data plane in the VPLS is the same as described in Section 4.2 of
   [RFC4761], and data plane processing for a PW is the same as
   described at the end of Section 6.

8. OAM Considerations

   VPLS OAM requirements and framework as specified in [RFC6136] are
   applicable to E-Tree, as both Ethernet OAM frames and data traffic
   are transported over the same PW.

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   Ethernet OAM for E-Tree including both service OAM and segment OAM
   frames shall undergo the same VLAN mapping as the data traffic; and
   root VLAN SHOULD be applied to segment OAM frames so that they are
   not filtered.

9. Applicability

   The solution is applicable to both LDP VPLS [RFC4762] and BGP VPLS
   [RFC4761].

   The solution is applicable to both "VPLS Only" networks and VPLS with
   Ethernet aggregation networks.

   The solution is also applicable to PBB VPLS networks.

10.  Security Considerations

   Besides security considerations as described in [RFC4448], [RFC4761]
   and [RFC4762], this solution prevents leaf to leaf communication in
   the data plane of VPLS when its PEs are interconnected with PWs. In
   this regard, security can be enhanced for customers with this
   solution.

11.  IANA Considerations

   IANA is requested to allocate a value for E-Tree in the registry of
   Pseudowire Interface Parameters Sub-TLV type.

   Parameter ID   Length       Description
   =======================================
   TBD            8            E-Tree

   IANA is requested to allocate two new LDP status codes from the
   registry of name "STATUS CODE NAME SPACE". The following values are
   suggested:

   Range/Value     E     Description
   ------------- -----   ----------------------
   TBD             1     E-Tree VLAN mapping not supported
   TBD             0     Leaf to Leaf PW released

   IANA is requested to allocate a value for E-Tree in the registry of
   BGP Extended Community.

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   Type Value          Name
   =======================================
   TBD                 E-Tree Info

12.  References

12.1.  Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4447] Martini, L., and et al, "Pseudowire Setup and Maintenance
             Using Label Distribution Protocol (LDP)", RFC 4447, April
             2006.

   [RFC4448] Martini, L., and et al, "Encapsulation Methods for
             Transport of Ethernet over MPLS Networks", RFC 4448, April
             2006.

   [RFC4761] Kompella, K. and Rekhter, Y., "Virtual Private LAN Service
             (VPLS) Using BGP for Auto-Discovery and Signaling", RFC
             4761, January 2007

   [RFC4762] Lasserre, M. and Kompella, V., "Virtual Private LAN
             Services using LDP", RFC 4762, January 2007.

   [RFC6136] Sajassi, A. and Mohan, D., "L2VPN OAM Requirements and
             Framework", RFC 6136, March 2011

12.2. Informative References

   [RFC3985] Bryant, S., and Pate, P., "Pseudo Wire Emulation Edge-to-
             Edge (PWE3) Architecture", RFC 3985, March 2005.

   [RFC4664] Andersson, L., and Rosen, E., "Framework for Layer 2
             Virtual Private Networks (L2VPNs)", RFC 4664, September
             2006.

   [RFC6246] Sajassi, A., and et al, "Virtual Private LAN Service (VPLS)
             Interoperability with Customer Edge (CE) Bridges", RFC 6246,
             June 2011

   [ETree-req] Key, R., et al, "Requirements for MEF E-Tree Support in
             VPLS", draft-ietf-l2vpn-etree-reqt-01, Work in Progress

   [Vpls-etree] Key, R., and et al, "Extension to VPLS for E-Tree",
             draft-key-l2vpn-vpls-etree-06, October 2011

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   [802.1aq] IEEE 802.1aq D4.3, Virtual Bridged Local Area Networks -
             Amendment 9: Shortest Path Bridging, September 2011

   [Etree-2PW] Ram, R., and et al., Extension to LDP-VPLS for E-Tree
             Using Two PW, draft-ram-l2vpn-ldp-vpls-etree-2pw-02, May
             2011

   [PBB-VPLS] Balus, F., and et al., Extensions to VPLS PE model for
             Provider Backbone Bridging, draft-ietf-l2vpn-pbb-vpls-pe-
             model-04, October 2011

13.  Acknowledgments

   The authors would like to thank Adrian Farrel, Susan Hares and Shane
   Amante for their valuable advices, thank Ben Mack-crane, Edwin
   Mallette, Donald Fedyk, Dave Allan, Giles Heron, Raymond Key, Josh
   Rogers, Sam Cao and Daniel Cohn for their valuable comments and
   discussions.

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Appendix A. Other PE Models for E-Tree

A.1. A PE Model With a VSI and No bridge

   If there is no bridge module in a PE, the PE may consist of Native
   Service Processors (NSPs) as shown in Figure A.1 (adapted from Fig. 5
   of [RFC3985]) where  any transformation operation for VLANs (e.g.,
   VLAN insertion/removal or VLAN mapping) may be applied. Thus a root
   VLAN or leaf VLAN can be added by the NSP depending on the UNI type
   (root/leaf) associated with the AC over which the packet arrives.

   Further, when a packet with a leaf VLAN exits a forwarder and arrives
   at the NSP, the NSP must drop the packet if the egress AC is
   associated with a leaf UNI.

   Tagged PW and VLAN mapping work in the same way as in the typical PE
   model.

           +----------------------------------------+
           |                PE Device               |
   Multiple+----------------------------------------+
   AC      |      |          |        Single        | PW Instance
   <------>o  NSP #          +      PW Instance     X<---------->
           |      |          |                      |
           |------|  VSI     |----------------------|
           |      |          |        Single        | PW Instance
   <------>o  NSP #Forwarder +      PW Instance     X<---------->
           |      |          |                      |
           |------|          |----------------------|
           |      |          |        Single        | PW Instance
   <------>o  NSP #          +      PW Instance     X<---------->
           |      |          |                      |
           +----------------------------------------+

        Figure A.1  A PE model with a VSI and no bridge module

   This PE model may be used by an MTU-s in an H-VPLS network, or an N-
   PE in an H-VPLS network with non-bridging edge devices, wherein a
   spoke PW can be treated as an AC in this model.

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A.2. A PE Model With external E-Tree interface

           +----------------------------------------+
           |                PE Device               |
   Root    +----------------------------------------+
   VLAN    |                 |        Single        | PW Instance
   <------>o                 +      PW Instance     X<---------->
           |                 |                      |
           |       VSI       |----------------------|
           |                 |        Single        | PW Instance
           |    Forwarder    +      PW Instance     X<---------->
           |                 |                      |
   Leaf    |                 |----------------------|
   VLAN    |                 |        Single        | PW Instance
   <------>o                 +      PW Instance     X<---------->
           |                 |                      |
           +----------------------------------------+

         Figure A.2  A PE model with external E-Tree interface

   A more simplified PE model is depicted in A.2, where Root/Leaf VLANs
   are directly or indirectly over a single PW connected to a same VSI
   forwarder in a PE, any transformation of E-Tree VLANs, e.g., VLAN
   insertion/removal or VLAN mapping, can be performed by some outer
   equipments, and the PE may further translate these VLANs into its own
   local VLANs. This PE model may be used by an N-PE in an H-VPLS
   network with bridging-capable devices, or scenarios such as providing
   E-Tree Network-to-Network (NNI) interfaces.

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   Authors' Addresses

   Yuanlong Jiang
   Huawei Technologies Co., Ltd.
   Bantian, Longgang district
   Shenzhen 518129, China
   Email: jiangyuanlong@huawei.com

   Lucy Yong
   Huawei USA
   1700 Alma Dr. Suite 500
   Plano, TX 75075, USA
   Email: lucyyong@huawei.com

   Manuel Paul
   Deutsche Telekom
   Winterfeldtstr. 21
   10781 Berlin, Germany
   Email: manuel.paul@telekom.de

   Frederic Jounay
   Orange CH
   4 rue caudray 1020 Renens, Switzerland
   Email: frederic.jounay@orange.ch

   Florin Balus
   Alcatel-Lucent
   701 E. Middlefield Road
   Mountain View, CA, USA 94043
   Email: florin.balus@alcatel-lucent.com

   Wim Henderickx
   Alcatel-Lucent
   Copernicuslaan 50
   2018 Antwerp, Belgium
   Email: wim.henderickx@alcatel-lucent.com

   Ali Sajassi
   Cisco
   170 West Tasman Drive
   San Jose, CA 95134, USA
   Email: sajassi@cisco.com

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