Redundancy provisioning for VPLS Inter-domain
draft-ietf-l2vpn-vpls-inter-domain-redundancy-02

Networking Working Group                                          Z. Liu
Internet-Draft                                             China Telecom
Intended status: BCP                                              L. Jin
Expires: January 13, 2014
                                                                 R. Chen
                                                                     ZTE
                                                                  D. Cai
                                                                S. Salam
                                                                   Cisco
                                                           July 12, 2013

             Redundancy provisioning for VPLS Inter-domain
            draft-ietf-l2vpn-vpls-inter-domain-redundancy-02

Abstract

   In many VPLS deployments based on [RFC4762], inter-domain
   connectivity has been deployed without node redundancy, or with node
   redundancy in a single domain.  This document describes a solution
   for inter-domain VPLS based on RFC4762 with node and link redundancy
   in both domains.

Status of this Memo

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   This Internet-Draft will expire on January 13, 2014.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of

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   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Conventions used in this document . . . . . . . . . . . . . . . 3
   3.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Network Use Case  . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  PW redundancy application procedure for inter-domain
       redundancy  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     5.1.  ICCP switchover condition . . . . . . . . . . . . . . . . . 6
       5.1.1.  Inter-domain PW failure . . . . . . . . . . . . . . . . 6
       5.1.2.  PE node isolation . . . . . . . . . . . . . . . . . . . 6
       5.1.3.  PE node failure . . . . . . . . . . . . . . . . . . . . 6
     5.2.  Inter-domain redundancy with two-PWs  . . . . . . . . . . . 6
     5.3.  Inter-domain redundancy with four-PWs . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 8
   7.  IANA Consideration  . . . . . . . . . . . . . . . . . . . . . . 8
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 9
     9.1.  Normative references  . . . . . . . . . . . . . . . . . . . 9
     9.2.  Informative references  . . . . . . . . . . . . . . . . . . 9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9

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1.  Introduction

   In many VPLS deployments based on [RFC4762], inter-domain
   connectivity has been deployed without node redundancy, or with node
   redundancy in a single domain.  This document describes a solution
   for inter-domain VPLS based on [RFC4762] with node and link
   redundancy in both domains.  The domain in this document refers to
   AS, or other administrative domains.

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.  Motivation

   Inter-AS VPLS offerings are widely deployed in service provider
   networks today.  Typically, the ASBRs and associated physical links
   that connect the domains carry a multitude of services.  As such, it
   is important to provide link and node redundancy, to ensure service
   high availability and meet end customer service level
   agreements(SLAs).

   Several current deployments of inter-AS VPLS are implemented using
   Inter-AS Option A, where VLANs are used to hand-off the services
   between two domains.  In these deployments, link/node redundancy is
   achieved using MC-LAG (Multi-Chassis Link Aggregation) and
   [I-D.ietf-pwe3-iccp].  This, however, places two restrictions on the
   interconnect: two domains must be interconnected using Ethernet
   links, and the links must be homogeneous, i.e. of the same speed, in
   order to be aggregate-able.  These two conditions cannot always be
   guaranteed in live deployments.  For instance, there are many
   scenarios where the interconnect between the domains uses POS (Packet
   over Sonet/SDH), thereby ruling out the applicability of MC-LAG as a
   redundancy mechanism.  As such, from a technical point of view, it is
   desirable to use PWs to interconnect the VPLS domains, and to offer
   resiliency using PW redundancy mechanisms.

   MP-BGP can be used for VPLS inter-domain protection, as described in
   [RFC6074], using either Option B or Option C inter-AS models.
   However, with this solution, the protection time relies on BGP
   control plane convergence.  In certain deployments, with tight SLA
   requirements on availability, this mechanism may not provide the
   desired failover time characteristics.  Furthermore, in certain
   situations MP-BGP is not deployed for VPLS.  The redundancy solution

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   described in this draft reuses ICCP [I-D.ietf-pwe3-iccp] and PW
   redundancy [RFC6718] to provide fast convergence.

   Furthermore, in the case where Label Switched Multicast is not used
   for VPLS multicast [I-D.ietf-l2vpn-vpls-mcast], the solution
   described here provides a better behavior compared to inter-AS option
   B: with option B, each PE must perform ingress replication to all
   other PEs in its local as well as the remote domain.  Whereas, with
   the ICCP solution, the PE only replicates to local PEs and to the
   ASBR.  The ASBR then sends traffic P2P to the remote ASBR, and the
   remote ASBR replicates to its local PEs.  As a result, the load of
   replication is distributed and is more efficient than option B.

   Two PW redundancy modes defined in [RFC6718], namely independent mode
   and master/slave mode, are applicable in this solution.  In order to
   maintain control plane separation between two domains, the
   independent mode is preferred by operators.  While the master/slave
   mode provides some enhanced capabilities and, hence, is included in
   this draft.

4.  Network Use Case

   There are two network use cases for VPLS inter-domain redundancy:
   two-PWs redundancy case, and four-PWs redundancy case.

   Figure 1 presents an example use case with two inter-domain PWs.
   PE3/PE4/PE5/PE6 may be ASBRs of their respective AS, or VPLS PEs
   within its own AS.  A deployment example of this use case is where
   there are only two physical links between two domains and PE3 is
   physically connected with PE5, and PE4 is physically connected with
   PE6.

                 +---------+                 +---------+
         +---+   | +-----+ |   active PW1    |  +-----+|    +---+
         |PE1|---|-| PE3 |-|-----------------|--| PE5 ||----|PE7|
         +---+\  |/+-----+ |                 |  +-----+\   /+---+
          |    \ /  | *    |                 |    * |  |\ /   |
          |     \|  | |ICCP|                 |ICCP| |  | \    |
          |    / \  | *    |                 |    * |  |/ \   |
         +---+/  |\+-----+ |                 |  +-----+/   \+---+
         |PE2|---|-| PE4 |-|-----------------|--| PE6 ||----|PE8|
         +---+   | +-----+ |   standby PW2   |  +-----+|    +---+
                 |         |                 |         |
                 |         |                 |         |
                 |  RG1    |                 |  RG2    |
                 +---------+                 +---------+

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                 operator A network             operator B network

                                 Figure 1

   Figure 2 presents a four-PWs inter-domain VPLS redundancy use-case.
   PE3/PE4/PE5/PE6 may be ASBRs of their respective AS, or VPLS PEs
   within its own AS, A deployment example of this use case is where
   there are four physical links between two domains and four PEs are
   physically connected with each other with four links.

                  +---------+                 +---------+
          +---+   | +-----+ |                 |  +-----+|    +---+
          |PE1|---|-| PE3 |-|--------PW1------|--| PE5 ||----|PE7|
          +---+\  |/+-----+ |-PW3-\   /-------|  +-----+\   /+---+
           |    \ /  | *    |      \ /        |    * |  |\ /   |
           |     \|  | |ICCP|       X         |ICCP| |  | \    |
           |    / \  | *    |      / \        |    * |  |/ \   |
          +---+/  |\+-----+ |-PW4-/   \-------|  +-----+/   \+---+
          |PE2|---|-| PE4 |-|----PW2----------|--| PE6 ||----|PE8|
          +---+   | +-----+ |                 |  +-----+|    +---+
                  |         |                 |         |
                  |         |                 |         |
                  |  RG1    |                 |  RG2    |
                  +---------+                 +---------+
                operator A network         operator B network

                                 Figure 2

5.   PW redundancy application procedure for inter-domain redundancy

   PW redundancy application procedures are described in section 9.1 of
   [I-D.ietf-pwe3-iccp].  When a PE node encounters a failure, the other
   PE takes over.  This document reuses the PW redundancy mechanism
   defined in[I-D.ietf-pwe3-iccp], with new ICCP switchover conditions
   as specified in following section.

   There are two PW redundancy modes defined in [RFC6870]: Independent
   mode and Master/Slave mode.  For the inter-domain four-PW scenario,
   it is required for PEs to ensure that the same mode is supported on
   two ICCP peers in the same RG.

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5.1.  ICCP switchover condition

5.1.1.  Inter-domain PW failure

   When a PE receives advertisements from the active PE, in the same RG,
   indicating that all the inter-domain PW status has changed to DOWN/
   STANDBY, then if it has the highest priority (after the advertising
   PE), it SHOULD advertise active state for all of its associated
   inter-domain PWs.

5.1.2.  PE node isolation

   When a PE detects failure of all PWs to the local domain, it SHOULD
   advertise standby state for all its inter-domain PWs to trigger
   remote PE to switchover.

5.1.3.  PE node failure

   When a PE node detects that the active PE, that is member of the same
   RG, has gone down, if the local PE has redundant PWs for the affected
   services and has the highest priority (after the failed PE), it
   advertises the active state for all associated inter-domain PWs.

5.2.  Inter-domain redundancy with two-PWs

   In this use case, it is recommended that the operation be as follows:
   o  ICCP deployment option: ICCP is deployed on VPLS edge nodes in
      both domains;
   o  PW redundancy mode: independent mode only;
   o  Protection architectures: 1:1(1 standby, 1 active).

   The switchover rules described in section 5.1 apply.  Before
   deploying this inter-domain VPLS, the operators MUST negotiate to
   configure same PW high/low priority at two PW end-points.  E.g, in
   figure 1, PE3 and PE5 MUST both have higher/lower priority than PE4
   and PE6, otherwise both PW1 and PW2 will be in standby state.

5.3.  Inter-domain redundancy with four-PWs

   In this use case, there are generally three options to provide 1:1
   protection or 3:1 protection.  The inter-domain PWs that connect to
   the same PE should have proper PW priority to advertise same active/
   standby state.  E.g, in figure 2, both PW1 and PW3 connected to PE3
   would advertise active/standby state.

   For 1:1 protection model, the operation would be as follows:

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   o  ICCP deployment option: ICCP is deployed on VPLS edge nodes in
      both domains;
   o  PW redundancy mode: independent mode only;
   o  Protection architectures: 1:1(1 standby, 1 active).

   The switchover rules described in section 5.1 apply.  In this case,
   the operators do not need to do any coordination of the inter-domain
   PW priority.  The PE detects one PW DOWN should set the other PW to
   STANDBY if available, and then synchronize the updated state to its
   ICCP peer.  When a PE detects that the PWs from ICCP peer PE are DOWN
   or STANDBY, it should switchover as described in section 5.1.1.

   There are two variants of the 3:1 protection model.  We will refer to
   them as option A and B. For option A of the 3:1 protection model, the
   support of 'request switchover' bit is required.  The operation is as
   follows:
   o  ICCP deployment option: ICCP is deployed on VPLS edge nodes in
      both domains;
   o  PW redundancy mode: Independent mode with 'request switchover' bit
      support;
   o  Protection architectures: 3:1 (3 standby, 1 active).

   In this case, the procedure on the PE for the PW failure is per
   section 6.3 of [RFC6870], and with the following additions:
   o  When the PE detects failure of the active inter-domain PW, it
      should switch to the other local standby inter-domain PW if
      available, and send an updated LDP pseudowire status message with
      the 'request switchover' bit set on that local standby inter-
      domain PW to the remote PE;
   o  Local and remote PE should also update the new PW status to their
      ICCP peers, respectively, in Application Data Messages with PW-RED
      Synchronization Request TLV for corresponding service, so as to
      synchronize the latest PW status on both PE sides;
   o  While waiting for the acknowledgment, the PE that sent the
      'request switchover' bit may receive a switchover request from its
      ICCP peer's PW remote endpoint by virtue of the ICCP
      synchronization.  The PE MUST compare IP addresses with that PW
      remote peer.  The PE with a higher IP address will ignore the
      request and continue to wait for the acknowledgement from its peer
      in the remote domain.  The PE with the lower IP address MUST clear
      'request switchover' bit and set 'Preferential Forwarding' local
      status bit, and update the PW status to ICCP peer.
   o  The remote PE receiving 'request switchover' bit will acknowledge
      the request and activate the PW only when it is ready to take over
      as described in section 5.1, otherwise, it MUST ignore the
      request.

   The node isolation failure and node failure is described in section

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   5.1.

   For option B of 3:1 protection model, master/slave mode support is
   required, and should be as follows:
   o  ICCP deployment option: ICCP is deployed on VPLS edge nodes in
      only one domain;
   o  PW redundancy mode: master/slave only;
   o  Protection architectures: 3:1 (3 standby, 1 active).

   When master/slave PW redundancy mode is employed, the network
   operators of two domains must agree on which domain PEs will be
   master, and configure the devices accordingly.  The inter-domain PWs
   that connect to one PE should have higher PW priority than the PWs on
   the other PE in the same RG.  The procedure on the PE for PW failure
   is as follows:
   o  The PE with higher PW priority should only enable one PW active,
      and the other PWs standby.
   o  When the PE detects active PW DOWN, it should enable the other
      local standby PW to be active with preference.  Only when two
      inter-domain PWs connect to the PE are DOWN, the ICCP peer PE in
      the same RG would switchover as described in section 5.1.

   The node isolation failure and node failure is described in section
   5.1.

6.  Security Considerations

   This draft will have the same security properties of
   [I-D.ietf-pwe3-iccp] and [RFC4762]

7.  IANA Consideration

   No IANA allocation is required in this draft.

8.  Acknowledgements

   The authors wish to acknowledge the contributions of Daniel Cohn and
   Yubao Wang.

      Daniel Cohn
      Orckit-Corrigent
      Email:daniel.cohn.ietf@gmail.com

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      Yubao Wang
      ZTE Corporation
      Email: wang.yubao@zte.com.cn

9.  References

9.1.  Normative references

   [I-D.ietf-pwe3-iccp]
              Martini, L., Salam, S., Sajassi, A., and S. Matsushima,
              "Inter-Chassis Communication Protocol for L2VPN PE
              Redundancy", draft-ietf-pwe3-iccp-11 (work in progress),
              February 2013.

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

   [RFC6870]  Muley, P. and M. Aissaoui, "Pseudowire Preferential
              Forwarding Status Bit", RFC 6870, February 2013.

9.2.  Informative references

   [I-D.ietf-l2vpn-vpls-mcast]
              Aggarwal, R., Rekhter, Y., Kamite, Y., and L. Fang,
              "Multicast in VPLS", draft-ietf-l2vpn-vpls-mcast-14 (work
              in progress), July 2013.

   [RFC4762]  Lasserre, M. and V. Kompella, "Virtual Private LAN Service
              (VPLS) Using Label Distribution Protocol (LDP) Signaling",
              RFC 4762, January 2007.

   [RFC6074]  Rosen, E., Davie, B., Radoaca, V., and W. Luo,
              "Provisioning, Auto-Discovery, and Signaling in Layer 2
              Virtual Private Networks (L2VPNs)", RFC 6074,
              January 2011.

   [RFC6718]  Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire
              Redundancy", RFC 6718, August 2012.

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Authors' Addresses

   Zhihua Liu
   China Telecom
   109 Zhongshan Ave.
   Guangzhou 510630
   P.R.China

   Email: zhliu@gsta.com

   Lizhong Jin
   Shanghai
   P.R.China

   Email: lizho.jin@gmail.com

   Ran Chen
   ZTE Corporation
   NO.19 East Huayuan Road
   Haidian District Beijing 100191
   P.R.China

   Email: chen.ran@zte.com.cn

   Dennis Cai
   Cisco
   3750 Cisco Way,
   San Jose, California 95134
   USA

   Email: dcai@cisco.com

   Samer Salam
   Cisco
   595 Burrard Street, suite 2123
   Vancouver, BC V7X 1J1
   Canada

   Email: ssalam@cisco.com

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