Network Working Group                         R. Ram, Orckit-Corrigent
Internet Draft                               D. Cohn, Orckit-Corrigent
Category: Standard Track                               R. Key, Telstra
                                                  P. Agarwal, Broadcom
Expires: November 18, 2011                                May 18, 2011




              Extension to LDP-VPLS for E-Tree Using Two PW
               draft-ram-l2vpn-ldp-vpls-etree-2pw-02.txt

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Copyright Notice



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   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]. 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 .................................................... 3
4. The 2-PW Solution .............................................. 4
5. Extension to VPLS for E-Tree.................................... 5
      5.1. AC E-Tree Type ......................................... 5
      5.2. VSI E-Tree Type and Identifier.......................... 5
         5.2.1. VSI E-Tree Type Encoding........................... 5
         5.2.2. VSI E-Tree Identifier Encoding..................... 6
      5.3. Additional Filtering in Data Forwarding................. 6
      5.4. Root/Leaf PWs Signaling................................. 7
      5.5. Supporting Remote AC.................................... 7
6. Backward Compatibility ......................................... 8
7. Compliance with Requirements.................................... 8
8. Security Considerations......................................... 8
9. IANA Considerations ............................................ 8
10. Acknowledgements .............................................. 8
11. References .................................................... 9
      11.1. Normative References................................... 9
      11.2. Informative References................................. 9







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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].

   [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 standard
   [RFC4762].

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

   The proposed solution is composed of three main components:

      - Current standard LDP-VPLS [RFC4762]
      - Extension to LDP-VPLS specified in this document
      - 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.

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


                   <--------------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


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   Extension to current VPLS standard [RFC4762] is required.

5. Extension to VPLS for E-Tree

5.1. 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.

5.2. 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 VSI interface.

   On reception, the two PWs SHALL be handled as the same logical VSI
   interface with respect to MAC address learning/forwarding, e.g.
   traffic SHALL NOT be forwarded between such PWs and MAC addresses
   arriving at one of the PWs SHALL be learned with a common logical
   VSI 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.

   The <VSI E-Tree type, VSI E-Tree identifier> pair SHALL be unique in
   PWs connecting a pair of VPLS PEs.

5.2.1. 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]).

   The field structure is defined as follows:






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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  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

5.2.2. 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 VSI interface,
   in the context of a pair of VPLS PEs.

   The reserved field SHALL be set to zero.

5.3. Additional Filtering in Data Forwarding

   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.




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     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.

5.4. 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 .               5.2. :

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

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

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

5.5. 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 VSI
   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.


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   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.

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

6. Backward Compatibility

   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 root/leaf.

   In a case where one of the peers do not support E-Tree, VSI E-Tree
   type and identifier parameters SHALL NOT be used.

7. 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 co-exist
   on any PE.

   The solution is applicable to LDP-VPLS [RFC4762].

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

8. Security Considerations

   This will be added in later version.

9. 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.

10. Acknowledgements

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


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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., 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

11.2. Informative References

   [Draft VPLS ETree Req]  Key, et al., Requirements for MEF E-Tree
   Support in VPLS, draft-key-l2vpn-vpls-etree-reqt-01.txt, September
   2010

   Authors' Addresses

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

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

   Raymond Key
   Telstra
   242 Exhibition Street, Melbourne
   VIC 3000, Australia
   Email: raymond.key@team.telstra.com

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






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