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Versions: (draft-jiang-l2vpn-vpls-pe-etree) 00 01 02 03 04 05 06 07 08 09 10 11 RFC 7796

Internet Working Group                                   Y. Jiang, Ed.
Internet Draft                                                 L. Yong
Intended status: Standards Track                                Huawei
                                                               M. Paul
                                                      Deutsche Telekom
Expires: August 2015                                 February 26, 2015


    Ethernet-Tree (E-Tree) Support in Virtual Private LAN Service (VPLS)
                   draft-ietf-l2vpn-vpls-pe-etree-05.txt


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Abstract

   A generic Virtual Private LAN Service (VPLS) solution is specified
   for Ethernet-Tree (E-Tree) services which uses VLANs to indicate root
   or 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.   Conventions used in this document ......................... 2
   2.   Terminology ............................................... 3
   3.   Introduction .............................................. 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.   Signaling for E-Tree Support ............................. 14
      6.1. LDP Extensions for E-Tree Support ..................... 14
      6.2. BGP Extensions for E-Tree Support ..................... 16
   7.   OAM Considerations ....................................... 18
   8.   Applicability ............................................ 18
   9.   Security Considerations .................................. 18
   10.  IANA Considerations ...................................... 19
   11.  References ............................................... 19
      11.1.   Normative References ............................... 19
      11.2.   Informative References ............................. 20
   12.  Acknowledgments .......................................... 21
   Appendix A. Other PE Models for E-Tree ........................ 22
      A.1. A PE Model With a VSI and No bridge ................... 22
      A.2. A PE Model With external E-Tree interface ............. 23



1. 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].


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2. Terminology

   AC: Attachment Circuit

   B-VLAN: Backbone VLAN

   C-VLAN: Customer VLAN

   E-Tree: Ethernet 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, also known as forwarding table

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

   Leaf AC: an AC attached with a leaf

   Leaf VLAN: a VLAN Identifier (ID) used to indicate all the frames
   that are originated at a leaf AC

   OAM: Operations, Administration and Maintenance

   PBB: Provider Backbone Bridge

   PE: Provider Edge

   PW: Pseudo Wire

   Root AC: an AC attached with a root

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

   S-VLAN: Service VLAN

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

   VLAN: Virtual Local Area Network

   VPLS: Virtual Private LAN Service

   VSI: Virtual Switching Instance as defined in [RFC4664], also known
   as VPLS Forwarder in [RFC7041]




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3. Introduction

   The Ethernet-Tree (E-Tree) service is defined in Metro Ethernet Forum
   (MEF) Technical Specification MEF 6.1 as a Rooted-Multipoint Ethernet
   Virtual Connection (EVC) service. It is a multipoint Ethernet service
   with special restrictions: the Ethernet 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 Virtual Private Multicast Service (VPMS) [VPMS] or Point-to-
   Multipoint (P2MP) multicast is a somewhat simplified version of this
   service, in fact, there is no exact corresponding terminology in IETF
   yet.

   [RFC7152] gives the requirements for providing E-Tree solutions in
   the VPLS and the need to filter leaf-to-leaf traffic. [RFC7387]
   further describes a Multiprotocol Label Switching (MPLS) framework
   for providing E-Tree. Though there were proposals on using PW control
   word or PWs to indicate the root/leaf attribute of an E-Tree frame,
   both methods are limited in that they 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 [802.1Q-2011], 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-
   2003). In the new IEEE 802.1Q solution, VLANs are used to indicate
   root/leaf attribute of a frame: 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 the new IEEE 802.1Q solution.

   This document specifies how the Ethernet VLAN solution can be used to
   support generic E-Tree services in VPLS. The solution specified here
   is fully compatible with the IEEE bridge architecture and with IETF
   Pseudo Wire Emulation Edge-to-Edge (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


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   scalability and simplicity are 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 VPLS.

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



4. PE Model with E-Tree Support

   The problem scenario of E-Tree as shown in Fig. 1 of [RFC7152] is a
   simplification of the L2VPN architecture, several common VPLS PE
   architectures are discussed in more details in [RFC4664] and
   [RFC6246].

   Therefore, E-Tree solution in VPLS is demonstrated with the help of a
   typical VPLS PE model. It can also be used in 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 (both figures are extracted from
   [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  |
                      |                               |
           +---+  AC  |  +------+      +-----------+  |
           |CE |---------|C-VLAN|------|           |  |
           +---+      |  |bridge|------|           |  |
                      |  +------+      |           |  |
                      |     o          |   S-VLAN  |  |
                      |     o          |           |  | ---> to VSI
                      |     o          |   Bridge  |  |
           +---+  AC  |  +------+      |           |  |
           |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 is
   difficult, sometimes even impossible.



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   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
   [802.1Q-2011] 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
   specified. 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 (frames over this port are untagged) or VLAN-
   unaware port (VLAN tags in the frames are ignored), the Ethernet
   frames received from the root ACs SHOULD be tagged with a root C-VLAN,
   and optionally MAY be added with another root S-VLAN.

   For a C-VLAN tagged port, the Ethernet frames received from the root
   ACs SHOULD be added with a root S-VLAN.

   For an S-VLAN tagged port, the S-VLAN tag in the Ethernet frames
   received from the root ACs SHOULD be translated to the root S-VLAN in
   the VPLS network domain. Alternatively, the PBB VPLS PE model (where
   an IEEE 802.1ah bridge module is embedded in the PE) as described in
   [RFC7041] MAY be used, and a root B-VLAN or leaf B-VLAN MAY be added
   in this case (the E-Tree attribute may also be indicated with two I-


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   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 [RFC7041] 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 uses 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 SHOULD work in the
   tagged mode (PW type 0x0004) as described in [RFC4448], in which case
   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 also 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.

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


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   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
   Operational Support 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        |
                  |                            |
        +----+    | +------+ Root VLAN +-----+ |    PW
        |Root|------| VLAN |-----------|T-VSI|----------
        +----+    | | BRG  | Leaf VLAN |     |----------
        +----+    | |      |-----------|     |----------
        |Leaf|------|      |           |     |-----+
        +----+    | +------+           +-----+ |   |
                  |                            |   |
                  +----------------------------+   |
                                                   |
                  +----------------------------+   |
                  |  VPLS PE with T-VSI        |   |
                  |                            |   |
        +----+    | +------+ Root VLAN +-----+ |   | PW
        |Root|------| VLAN |-----------|T-VSI|-----+
        +----+    | | BRG  | Leaf VLAN |     |----------
        +----+    | |      |-----------|     |----------
        |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 [802.1Q-2011].

    The signaling for VLANs used by E-Tree is specified in Section 6.



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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.
   A raw PW SHOULD be used to connect them.


                  +------------------------+
                  |  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 (both have E-Tree capability) are inter-connected and
   one of them (e.g., PE2) is attached with only leaf nodes, as shown in
   the scenario of Fig. 7, its peer PE (e.g., PE1) should then work in
   the optimized 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. Signaling for E-Tree Support

6.1. LDP Extensions for E-Tree Support

   In addition to the signaling procedures as specified in [RFC4447],
   this document specifies 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(0x1A) |   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 (0x1A) as 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 peer 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, after saving the VLAN information for the PW, 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.

6.2. BGP Extensions for E-Tree Support

   A new E-Tree extended community (0x800b) is allocated by IANA for E-
   Tree signaling in BGP VPLS:

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


                     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, 14 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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   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.

   The PEs attached with both leaf and root nodes MUST support BGP E-
   Tree signaling as described in this document, and SHOULD support VLAN
   mapping in their data planes. The traditional PE attached with only
   root nodes may also participate in an E-Tree service. If some PEs
   don't support VLAN mapping, global VLANs as per Section 5.2 MUST be
   provisioned for 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, after saving the VLAN information for the
   PW, 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 {

          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 {

                     Log with a message "E-Tree VLAN mapping not
                     supported" and exit the process;

                     }

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

      }

   3) If the P bit is set {



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          If the PE is a leaf-only PE itself, then forbids any traffic on
          the PW;

          Else 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 6.1.

7. 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.

   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.

8. Applicability

   The solution specified in this document is applicable to both LDP
   VPLS [RFC4762] and BGP VPLS [RFC4761].

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

   This solution is also applicable to PBB VPLS networks.

9. 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.





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10.  IANA Considerations

   IANA allocated a value for E-Tree in the registry of Pseudowire
   Interface Parameters Sub-TLV type.

   Parameter ID   Length       Description
   =======================================
   0x1A            8            E-Tree


   IANA allocated two new LDP status codes from the registry of name
   "STATUS CODE NAME SPACE".


   Range/Value     E     Description
   ------------- -----   ----------------------
   0x20000003      1     E-Tree VLAN mapping not supported
   0x20000004      0     Leaf to Leaf PW released

   IANA allocated a value for E-Tree in the registry of BGP Extended
   Community.

   Type Value   Sub-Type Value   Name
   ==========   ==============   ============
   0x80         0x0b             E-Tree Info

11.  References

11.1.  Normative References

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

   [RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and Heron,
             G., "Pseudowire Setup and Maintenance Using Label
             Distribution Protocol (LDP)", RFC 4447, April 2006.

   [RFC4448] Martini, L., Rosen, E., El-Aawar, N., and Heron,G.,
             "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.



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

11.2. 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., Brockners, F., Mohan, D., and Serbest, Y.,
             "Virtual Private LAN Service (VPLS) Interoperability with
             Customer Edge (CE) Bridges", RFC 6246, June 2011.

   [RFC7041] Balus, F., Sajassi, A., and Bitar, N., Extensions to VPLS
             PE model for Provider Backbone Bridging, RFC 7041, November
             2013.

   [RFC7152] Key, R., DeLord, S., Jounay, F., Huang, L., Liu, Z., and M.
             Paul, "Requirements for Metro Ethernet Forum (MEF)
             Ethernet-Tree (E-Tree) Support in Layer 2 Virtual Private
             Network (L2VPN)", RFC 7152, March 2014.

   [RFC7387] Key, R., Yong, L., DeLord, S., Jounay, F., and Jin, L., "A
             Framework for Ethernet Tree (E-Tree) Service over a
             Multiprotocol Label Switching (MPLS) Network", RFC 7387,
             October 2014.

   [802.1Q-2011] IEEE 802.1Q, Media Access Control (MAC) Bridges and
             Virtual Bridge Local Area Networks, August 2011.

   [MEF4]    Metro Ethernet Forum, Metro Ethernet Network Architecture
             Framework - Part 1: Generic Framework, Technical
             Specification MEF 4, May 2004.

   [MEF6.1]  Metro Ethernet Forum, "Ethernet Services Definitions -
             Phase 2", Technical Specification MEF 6.1, April 2008.

   [VPMS]    Kamite, Y., Jounay, F., Niven-Jenkins, B., Brungard, D.,
             and L. Jin, "Framework and Requirements for Virtual Private
             Multicast Service (VPMS)", Work in Progress, draft-ietf-
             l2vpn-vpms-frmwk-requirements-05, October 2012.






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12.  Acknowledgments

   The authors would like to thank Stewart Bryant for his detailed
   review and suggestions, 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 User
   Network Interface (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 a Multi-Tenant Unit switch (MTU-s) in a
   Hierarchical VPLS (H-VPLS) network, or a Network-facing PE (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 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
   207 Estrella Xing
   Georgetown TX, USA 78628
   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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