Network Working Group                       Rafi Ram, Orckit-Corrigent
Internet Draft                           Daniel Cohn, Orckit-Corrigent
Category: Standard Track                           Raymond Key, Huawei
                                                  P. Agarwal, Broadcom
                                      Yuqun (Sam) Cao, Ruijie Networks
Expires: September 5, 2012                       Josh Rogers, TW Cable

                                                           Mar 5, 2012


             Extension to VPLS for E-Tree Using Multiple PWs
                  draft-ram-l2vpn-etree-multiple-pw-01

Status of this Memo

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

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Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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


Abstract

   This document proposes a solution for Metro Ethernet Forum (MEF)
   Ethernet Tree (E-Tree) support in Virtual Private LAN Service using
   LDP Signaling (LDP-VPLS) [RFC4762],BGP signaling (BGP-VPLS) [RFC4761]
   or BGP auto-discovery (BGP-AD) [RFC6074]. The proposed solution is
   characterized by the use of two PWs between a pair of PEs. This
   solution is applicable for both VPLS and H-VPLS.


Table of Contents


1. Introduction ................................................... 3
2. Conventions used in this document............................... 3
3. The Problem .................................................... 4
4. The 2-PW Solution .............................................. 5
5. AC E-Tree Type ................................................. 6
6. Extension to LDP-VPLS for E-Tree................................ 6
      6.1. VSI E-Tree Type and Identifier ..........................6
         6.1.1. VSI E-Tree Type Encoding........................... 6
         6.1.2. VSI E-Tree Identifier Encoding .....................7
      6.2. Root/Leaf PWs Signaling................................. 7
      6.3. Supporting Remote AC.................................... 8
7. Extension to BGP-VPLS for E-Tree................................ 9
      7.1. Auto-discovery ......................................... 9
      7.2. PW Setup and Teardown................................... 9
      7.3. Root/Leaf PWs Signaling................................ 10
      7.4. Optimization .......................................... 10
8. Extension to BGP-AD for E-Tree................................. 10
      8.1. Auto-discovery ........................................ 10
      8.2. PW Setup and Teardown.................................. 11
      8.3. Optimization .......................................... 11
9. Data Forwarding Requirements................................... 11
10. Backward Compatibility........................................ 12
      10.1. LDP-VPLS ............................................. 12
      10.2. BGP-VPLS ............................................. 12
      10.3. BGP-AD ............................................... 12

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11. Compliance with Requirements.................................. 12
12. Security Considerations....................................... 13
13. IANA Considerations .......................................... 13
14. Acknowledgements ............................................. 13
15. References ................................................... 13
      15.1. Normative References.................................. 13
[RFC6074]  Rosen, Davie, Radoaca and Luo, Provisioning, Auto-Discovery,
and Signaling in Layer 2 Virtual Private Networks (L2VPNs), January
2011 ............................................................. 13
      15.2. Informative References................................ 13

1. Introduction

   This document proposes a solution for Metro Ethernet Forum (MEF)
   Tree (E-Tree) support in Virtual Private LAN Service using LDP
   Signaling (LDP-VPLS) [RFC4762], BGP Signaling (BGP-VPLS) [RFC4761]
   or BGP auto-discovery (BGP-AD) [RFC6074].

   [Draft ETree VPLS Req] is used as requirement specification.

   The proposed solution is characterized by the use of two PWs between
   a pair of PEs, which requires extension to the current VPLS
   standards [RFC4762],[RFC4761] and [RFC6074].

   This solution is applicable for both VPLS and H-VPLS.

   The proposed solution is composed of three main components:

     o Current VPLS standards: LDP-VPLS [RFC4762],BGP-VPLS [RFC4761]
        and BGP-AD [RFC6074]

     o Extensions to the above specified in this document

     o PE local split horizon mechanism

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 RFC-2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.





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3. The Problem

   [Draft ETree VPLS Req] identifies the problem when there are two or
   more PEs with both Root AC and Leaf AC.














































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                       <-----------E-Tree---------->

                        +---------+        +---------+
                        |   PE1   |        |   PE2   |
        +---+           |  +---+  |        |  +---+  |           +---+
        |CE1+----AC1----+--+   |  |        |  |   +--+----AC3----+CE3|
        +---+ (Root AC) |  | V |  |        |  | V |  | (Root AC) +---+
                        |  | S +--+--PW----+--+ S |  |
        +---+           |  | I |  |        |  | I |  |           +---+
        |CE2+----AC2----+--+   |  |        |  |   +--+----AC4----+CE4|
        +---+ (Leaf AC) |  +---+  |        |  +---+  | (Leaf AC) +---+
                        +---------+        +---------+

         Figure 1: Problem Scenario for Leaf-to-Leaf Communication
                                Restriction

   When PE2 receives a frame from PE1 via the Ethernet PW:

     o PE2 does not know whether the ingress AC is a Leaf AC or not

     o PE2 does not have sufficient information to enforce the Leaf-
        to-Leaf communication restriction

4. The 2-PW Solution

   A simple fix is to carry additional information with each frame on
   the PW, indicating whether the frame is originated from a Leaf AC or
   a Root AC on the ingress PE.

   The proposed solution uses a pair of PWs to interconnect two VPLS
   PEs:

     o First PW is used for frames originated from Root ACs

     o Second PW is used for frames originated from Leaf ACs














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              <--------------E-Tree-------------->
                   +---------+              +---------+
                   |   PE1   |              |   PE2   |
   +---+           |  +---+  |              |  +---+  |           +---+
   |CE1+----AC1----+--+   |  |              |  |   +--+----AC3----+CE3|
   +---+ (Root AC) |  | V +--+-VSI Root PW -+--+ V |  | (Root AC) +---+
                   |  | S |  |              |  | S |  |
   +---+           |  | I +--+-VSI Leaf PW -+--+ I |  |           +---+
   |CE2+----AC2----+--+   |  |              |  |   +--+----AC4----+CE4|
   +---+ (Leaf AC) |  +---+  |              |  +---+  | (Leaf AC) +---+
                   +---------+              +---------+

   Figure 2: Two-PW Solution for Leaf-to-Leaf Communication Restriction

   The next sections specify the required extension to current VPLS
   standards.

5. AC E-Tree Type

   Each AC connected to a specific VPLS instance on a PE MUST have an
   AC E-Tree Type attribute, either Leaf AC or Root AC. For backward
   compatibility, the default AC E-Tree Type MUST be Root.

   This AC E-Tree Type is locally configured on a PE and no signaling
   is required between PEs.

6. Extension to LDP-VPLS for E-Tree

   This section specifies extensions to LDP-VPLS [RFC 4762] to support
   E-Tree requirements. These extensions apply to both FEC types
   specified in [RFC 4762], namely PWid and generalized PWid.

6.1. VSI E-Tree Type and Identifier

   Two new PW interface parameters (as defined in section 5.5 of
   [RFC4447]) are defined for use in E-Tree VPLS: VSI E-Tree type and
   VSI E-Tree identifier.

   VSI E-Tree type can be either root or leaf and identifies VSI root
   PW and VSI leaf PW respectively, as defined in section 4.

   VSI E-tree identifier is a number that is used to identify a pair of
   root and leaf PW as part of the same logical bridge interface.

   The <VSI E-Tree identifier, VSI E-Tree type> pair SHALL be unique
   among PWs connecting a pair of VPLS PEs for the same VPLS instance.

6.1.1. VSI E-Tree Type Encoding

   The VSI E-Tree type field is encoded as an interface parameters sub-
   TLV (as defined in section 5.5 of [RFC4447]).

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   The field structure is defined 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Type (TBD)   |    Length (1) |        VSI E-Tree Type        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   VSI E-tree Type can take the following values:

   0 E-Tree Root VSI

   1  E-Tree Leaf VSI

6.1.2. VSI E-Tree Identifier Encoding

   The VSI E-Tree identifier field is encoded as an interface
   parameters sub-TLV (as defined in section 5.5 of [RFC4447]).

   The field structure is defined 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Type (TBD)   |    Length (1) |     VSI E-Tree Identifier     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  VSI E-Tree Identifier(cont.) |           Reserved            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   VSI E-tree Identifier is a 32-bit number that is used to identify a
   pair of root and leaf PW as part of the same logical bridge
   interface, in the context of a pair of VPLS PEs.

   The reserved field SHALL be set to zero.

6.2. Root/Leaf PWs Signaling

   Signaling of root and leaf PWs is required only when two PWs are
   used for interconnecting between pair of VSIs. As explained in
   section 6.1:

     o Root VSI E-Tree type SHALL be used to signal a root PW.

     o Leaf VSI E-Tree type SHALL be used to signal a leaf PW.

   PW type signaling rules remain as defined in [RFC4447].



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   When the generalized PWid encoding (FEC 129) is used, AII shall be
   set to 1 for the leaf PW.

   It should be noted that in a full-mesh VPLS (as opposed to H-VPLS),
   the following VSI pair types do not require two interconnecting PWs:

   Root-only VSI <-> any VSI: only root PW required

   Leaf-only VSI <-> leaf-only VSI: no PWs required

   Where root-only VSI is a VSI where all ACs are of the root type, and
   leaf-only VSI is one where all ACs are of the leaf type.

6.3. Supporting Remote AC

   When PW is used to interconnect between VSI and a remote AC (e.g.
   the PW1, PW2 in Figure 3), an Ethernet Raw or Ethernet tagged PW
   types SHALL be used as defined in [RFC4762].

                <----------------------E-Tree---------->
                           +-------+            +-------+
                 +----+    |  PE1  |            |  PE2  |
   +---+         |    |    | +---+ |            | +---+ |
   |CE1+---AC1---+----+PW1-+-+   | |            | |   | |         +---+
   +---+(Root AC)|    |    | |   | |            | |   +-+---AC4---+CE4|
                 |PE-r|    | | V +-+VSI Root PW-+-+ V | |(Root AC)+---+
   +---+         |    |    | |   | |            | |   | |
   |CE2+---AC2---+----+PW2-+-+ S | |            | | S | |
   +---+(Leaf AC)|    |    | |   | |            | |   | |
                 +----+    | | I +-+VSI Leaf PW-+-+ I | |
   +---+                   | |   | |            | |   | |         +---+
   |CE3+--------AC3--------+-+   | |            | |   +-+---AC5---+CE5|
   +---+     (Leaf AC)     | +---+ |            | +---+ |(Leaf AC)+---+
                           +-------+            +-------+


                Figure 3: VPLS with Remote AC Connectivity

   In addition, the AC type i.e. Root or leaf, SHALL be locally
   provisioned on the VSI side to specify the remote AC E-Tree Type per
   PW. Moreover, such PWs that are used for interconnecting between a
   remote AC and a VSI SHALL considered as separate logical bridge
   interfaces with respect to MAC address learning/forwarding e.g.
   traffic forwarding between such PWs is allowed as long as they are
   not both defined as Leaf.

   In Figure 3, AC1 is remotely interconnected to the VPLS service via
   PW1, and AC2 is remotely interconnected to the VPLS service via PW2.

   AC1 is a Root AC and therefore the local type for PW1 in PE1 SHALL
   be Root.

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   AC2 is a Leaf AC and therefore the local type for PW2 in PE1 SHALL
   be Leaf.

7. Extension to BGP-VPLS for E-Tree

   This section specifies extensions to BGP-VPLS [RFC 4761] to support
   E-Tree requirements.

7.1. Auto-discovery

   Requirements in section 3.2.2 of [RFC 4761] apply, with the
   following modifications.

   A PE SHALL advertise two NLRIs for each E-Tree VPLS instance, with
   the same VE-ID and non-overlapping label blocks. The PE SHALL
   indicate that one of the NLRIs signals a root PW and the other one
   signals a leaf PW by setting the E-Tree type field in the attached
   Layer2 Info Extended Community, as specified in section 7.2. A
   special E-tree type is used for the leaf PW when only leaf ACs exist
   in the VPLS instance, as specified in section 7.2.

7.2. PW Setup and Teardown

   Requirements in section 3.2.3 of [RFC4761] apply, with the following
   modifications.

   If a PE receives two VPLS NLRI announcements for an E-Tree VPLS
   instance from a remote PE with the same VE-ID and different
   root/leaf indication, the PE SHALL set up two PWs to the remote PE.

   If a PE with an E-Tree VPLS instance with only leaf ACs receives a
   VPLS NLRI announcement for this instance from a remote PE with the
   leaf-only indication, no PWs shall be set up to the remote PE. This
   rule overrides the previous one.

   If a PE receives a legacy VPLS NLRI  for an E-Tree VPLS instance
   from a remote PE, it will withdraw the Leaf or leaf-only VPLS NLRI
   it previously advertised and set up only a root PW to the remote PE.

   PW setup for each of the PWs follows the rules in 3.2.3 of
   [RFC4761].

   A PW established following the receipt of a VPLS NLRI with root
   indication will be known as root PW.

   A PW established following the receipt of a VPLS NLRI with leaf or
   leaf-only indication will be known as leaf PW.



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   Two PWs established following the receipt of VPLS NLRIs with the
   same VE-ID SHALL be associated to the same logical bridge interface.

7.3. Root/Leaf PWs Signaling

   The Layer2 Info Extended Community attribute is used to indicate
   root/leaf assignment for the associated VPLS NLRI.

   With reference to Figure 4, bits 4-5 in the control flags are
   defined for E-Tree type (ET) signaling. Bits C, S have been defined
   in [RFC4761].

           0 1 2 3 4 5 6 7
          +-+-+-+-+-+-+-+-+
          |  MBZ  |ET |C|S|      (MBZ = MUST Be Zero)
          +-+-+-+-+-+-+-+-+

                        Figure 4 - Control Flags Bit Vector

   ET can take the following values:

   0 Legacy VPLS NLRI: This PE does not support E-Tree extensions.

   1  E-Tree Leaf-only VPLS NLRI: there are only leaf ACs in the VSI,
   and this is the E-Tree Leaf VPLS NLRI.

   2  E-Tree Root VPLS NLRI: there are root ACs in the VSI, and this is
   the E-Tree Root VPLS NLRI.

   3  E-Tree Leaf VPLS NLRI: there are root ACs in the VSI, and this is
   the E-Tree Leaf VPLS NLRI.

7.4. Optimization

   As in the LDP case (section 6.2), root and leaf PWs need not be
   established between every VSI pair. Procedures in this draft avoid
   the establishment of PWs between leaf-only VSIs, but they do not
   avoid establishment of leaf PW between root-only VSI and any other
   VSI. This is a consideration for future versions of the draft.

8. Extension to BGP-AD for E-Tree

   This section specifies extensions to BGP-AD [RFC6074] to support E-
   Tree requirements.

8.1. Auto-discovery

   Requirements in section 3.3.2.1 of [RFC6074] apply, with the
   following modifications.


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   Each PE with SHALL advertise two NLRIs for each VPLS instance, with
   the same VE-ID.

   The PE SHALL indicate that one of the NLRIs advertises a root
   attachment and the other one a leaf attachment by setting the
   PE_addr field to zero and one respectively in the NLRIs.

8.2. PW Setup and Teardown

   Requirements in section 3.3.3 of [RFC6074] apply, with the following
   modifications.

   If a PE receives two VPLS NLRI announcements from a remote PE with
   the same VE-ID and different root/leaf indication, the PE SHALL set
   up two PWs to the remote PE. PW setup for each of the PWs follows
   the rules in 3.3.3 of [RFC6074].

   A PW established following the receipt of a VPLS NLRI with root
   indication will be known as root PW.

   A PW established following the receipt of a VPLS NLRI with leaf
   indication will be known as leaf PW.

   Two PWs established following the receipt of VPLS NLRIs with the
   same VE-ID SHALL be associated to the same logical bridge interface.

8.3. Optimization

   As in the LDP case (section 6.2), root and leaf PWs need not be
   established between every VSI pair. However, BGP-AD optimization to
   avoid root or leaf PW setup in these cases is not considered in this
   draft and is left as a consideration for future versions.

9. Data Forwarding Requirements

   On frame reception, two PWs associated to the same logical bridge
   interface SHALL be handled as a single bridge interface with respect
   to MAC address learning/forwarding, e.g. traffic SHALL NOT be
   forwarded between such PWs and MAC addresses in frames arriving at
   any of the PWs SHALL be learned on a common logical bridge
   interface.

   On transmission, the VPLS processing entity SHALL send root-
   originated traffic via the root PW, and SHALL send leaf-originated
   traffic via the leaf PW.




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   An egress PE SHALL NOT deliver a frame originated at a leaf AC to
   another leaf AC.

   The following specifies how AC E-Tree type per frame is determined:

     o A frame received from a root PW indicates that the frame was
        originated from a root AC.

     o A frame received from a leaf PW indicates that the frame was
        originated from a leaf AC.

     o For the case where both ingress AC and egress AC are on the
        same PE, local split horizon implementation on the PE will be
        sufficient, and is not further discussed in this document.

10. Backward Compatibility

10.1. LDP-VPLS

   Root or leaf VSI E-Tree type and identifier parameters SHALL be used
   only in cases where both PEs are VPLS capable and both support E-
   Tree extensions defined in this document.

10.2. BGP-VPLS

   VPLS NLRIs with root/leaf indication are transmitted only to remote
   PEs that support E-Tree extensions defined in this document.

10.3. BGP-AD

   VPLS NLRIs with root/leaf indication SHALL be transmitted only to
   remote PEs that support E-Tree extensions defined in this document.

11. Compliance with Requirements

   This refers to [Draft ETree VPLS Req] Section 5 Requirements.

   The solution prohibits communication between any two Leaf ACs in a
   VPLS instance.

   The solution allows multiple Root ACs in a VPLS instance.

   The solution allows Root AC and Leaf AC of a VPLS instance to co-
   exist on any PE.

   The solution is applicable to LDP-VPLS [RFC4762], BGP-VPLS [RFC4762]
   and BGP-AD [RFC6074].

   The solution is applicable to Case 1: Single technology "VPLS Only".


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12. Security Considerations

   This will be added in later version.

13. IANA Considerations

   Additional assignments will be required for the new interface
   parameter sub-TLV types introduced in Section 4.2. Details will be
   added in a later version.

14. Acknowledgements

   The authors wish to acknowledge the contributions of Luca Martini
   and Amir Halperin.

15. References

15.1. 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 al, Pseudowire Setup and Maintenance
   Using the Label Distribution Protocol (LDP), April 2006

   [RFC4762]  Lasserre & Kompella, Virtual Private LAN Service (VPLS)
   Using Label Distribution Protocol (LDP) Signaling, January 2007

   [RFC4761]  Rekhter & Kompella, Virtual Private LAN Service (VPLS)
   Using BGP for Auto-Discovery and Signaling, January 2007

   [RFC6074]  Rosen, Davie, Radoaca and Luo, Provisioning, Auto-
   Discovery, and Signaling in Layer 2 Virtual Private Networks
   (L2VPNs), January 2011

15.2. Informative References

   [Draft VPLS ETree Req]  Key, et al., Requirements for MEF E-Tree
   Support in VPLS, draft-key-l2vpn-vpls-etree-reqt-04, September 2011

   Authors' Addresses

   Rafi Ram
   Orckit-Corrigent
   126 Yigal Alon St.
   Tel Aviv, Israel
   Email: rafir@orckit.com


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   Daniel Cohn
   Orckit-Corrigent
   126 Yigal Alon St.
   Tel Aviv, Israel
   Email: danielc@orckit.com

   Raymond Key
   Huawei
   Email: raymond.key@ieee.org

   Puneet Agarwal
   Broadcom
   3151 Zanker Road
   San Jose, CA 95134
   Email: pagarwal@broadcom.com

   Yuqun (Sam) Cao
   Ruijie Networks
   618 Jinshan Road, Fuzhou 350002, China
   Email: yuqun.cao@gmail.com

   Josh Rogers
   Time Warner Cable
   11921 N MoPac Expwy
   Austin, TX 78759
   USA
   Email: josh.rogers@twcable.com





















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