Redundancy provisioning for VPLS Inter-domain
draft-liu-l2vpn-vpls-inter-domain-redundancy-03

Networking Working Group                                          Z. Liu
Internet-Draft                                             China Telecom
Intended status: Standards Track                                  L. Jin
Expires: December 15, 2012                                       R. Chen
                                                                     ZTE
                                                                  D. Cai
                                                                S. Salam
                                                                   Cisco
                                                           June 13, 2012

             Redundancy provisioning for VPLS Inter-domain
            draft-liu-l2vpn-vpls-inter-domain-redundancy-03

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

   This Internet-Draft is submitted in full conformance with the
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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 15, 2012.

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   carefully, as they describe your rights and restrictions with respect
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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.  PW redundancy mode negotiation . . . . . . . . . . . . . .  5
     5.2.  ICCP switchover condition  . . . . . . . . . . . . . . . .  6
       5.2.1.  PW failure . . . . . . . . . . . . . . . . . . . . . .  6
       5.2.2.  PE node isolation  . . . . . . . . . . . . . . . . . .  6
       5.2.3.  PE node failure  . . . . . . . . . . . . . . . . . . .  6
     5.3.  Inter-domain redundancy with two Inter-domain PWs  . . . .  6
     5.4.  Inter-domain redundancy with Inter-domain four-PWs . . . .  7
     5.5.  MAC Withdraw procedure in VPLS Inter-domain  . . . . . . .  8
       5.5.1.  MAC Withdraw Capability TLV format . . . . . . . . . .  9
       5.5.2.  Optimized MAC Withdraw processing  . . . . . . . . . . 10
   6.  Load Balancing . . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   8.  IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 10
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     10.1. Normative references . . . . . . . . . . . . . . . . . . . 11
     10.2. Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12

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1.  Introduction

   In many VPLS deployment based on [RFC 4762], 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 [RFC 4762] with node and link
   redundancy in both domain.  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 the 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: the 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 [I-D.ietf-pwe3-redundancy] 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.

   The two PW redundancy modes defined in
   [I-D.ietf-pwe3-redundancy-bit], namely independent mode and master/
   slave mode, are applicable in this solution.  In order to maintain
   control plane separation between the 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,
   where there are only two physical links between the two domains.
   PE3/PE4/PE5/PE6 may be ASBRs of their respective AS, or VPLS PEs
   within its own AS, 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    |
               +---------+                       +---------+
               operator A network                operator B network

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                                 Figure 1

   Figure 2 presents a four-PWs inter-domain VPLS redundancy use-case,
   where there are four physical links between the two domains.  PE3/
   PE4/PE5/PE6 may be ASBRs of their respective AS, or VPLS PEs within
   its own AS, and the 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 draft reuses the PW redundancy mechanism defined
   in [I-D.ietf-pwe3-iccp], with new ICCP switchover conditions as
   specified in the following section, and also the corresponding MAC
   withdrawal mechanism.

5.1.  PW redundancy mode negotiation

   There are two PW redundancy modes defined in
   [I-D.ietf-pwe3-redundancy-bit]: Independent mode and Master/Slave
   mode.  For the inter-domain four-PW scenario, it is required for the
   PEs to advertise their redundancy mode configuration in order to
   ensure that the same mode is supported on the two ICCP peers in the
   same RG.

   [I-D.ietf-pwe3-iccp] section 7.1.3 defines PW-RED Config TLV.  This

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   draft proposes that the Flags field of the Config TLV be extended
   with two new values to indicated the PW redundancy mode configured on
   the PE for the associated PW:
   o  "0x04" to indicate independent PW redundancy mode configured.
   o  "0x08" to indicate Master/Slave PW redundancy mode configured.

   If the advertised values do not match among the PEs in the RG for a
   given ROID, then the implementation MUST alert the operator of mis-
   configuration.

5.2.  ICCP switchover condition

5.2.1.  PW failure

   When a PE receives advertisements from the active PE, in the same RG,
   indicating that all the 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.

5.2.2.  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, and send ICCP
   Application Data message to trigger remote PEs to switchover.

5.2.3.  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.

5.3.  Inter-domain redundancy with two Inter-domain 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 domain;
   o  PW redundancy mode: independent mode only;
   o  Protection architectures: 1:1 (1 standby, 1 active).

   The switchover rules described in section 5.2 apply.  Before
   deploying this inter-domain VPLS, the operators MUST negotiate to
   configure same PW high/low priority at the 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.

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

   The switchover rules described in section 5.2 apply.  In this case,
   the operator does not need to do any coordination of the inter-domain
   PW priority.  The PE detecting 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 5.2.1.

   There are two variants of the 3:1 protection model.  We will refer to
   them as options A and B. For option A of the 3:1 protection model,
   the support for 'request switchover' bit is required.  The operation
   is as follows:
   o  ICCP deployment option: ICCP is deployed on VPLS edge nodes in
      both domain;
   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 draft-ietf-pwe3-redundancy-bit-07, 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 remote the 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

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      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 !(R)request switchover!_ bit will
      acknowledge the request and activate the PW only when it is ready
      to take over as described in section 5.2, otherwise, it MUST
      ignore the request.

   The node isolation failure and node failure is described in section
   5.2.

   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 the 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 the two
      inter-domain PWs connect to the PE are DOWN, the ICCP peer PE in
      the same RG would switchover as described in section 5.2..

   The node isolation failure and node failure is described in section
   5.2.

5.5.   MAC Withdraw procedure in VPLS Inter-domain

   It MAY be desirable to remove or unlearn MAC addresses that have been
   dynamically learned for faster convergence.  This is accomplished by
   sending an LDP Address Withdraw Message.  PE SHOULD not advertise MAC
   Address Withdraw message from one domain to the other.
   Correspondingly, VPLS PE that connects another domain SHOULD also
   reject any MAC Address Withdraw message received from that domain.

   In figure 1, when the failure of the active PW is detected by PE3, it
   will trigger negative MAC Address Withdraw message
   [I-D.ietf-l2vpn-vpls-ldp-mac-opt].  By default, as per the processing
   rules defined in [RFC4762], upon PE4 activates the standby PW, it

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   will also send a MAC Address Withdraw message.  There would be two
   copies of MAC Address Withdraw messages received by each PE, which
   would make the network convergence worse.

   In order to determine which PE to send MAC Withdraw message, this
   draft introduce an MAC Withdraw Capability for LDP [RFC5561], a MAC
   Withdraw Capability TLV is used for negotiating the MAC withdraw
   capability.

5.5.1.   MAC Withdraw Capability TLV format

   The MAC Withdraw Capability TLV is described as below:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F| MAC withdraw Capability   |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |1| Reserved    |P|N|                 Reserved                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 3

   U-bit: set to "1".

   F-bit: set to "0".

   Once advertised, this capability cannot be withdrawn and hence the
   S-bit must always be set to 1 both in Initialization message and
   Capability message.

   MAC withdraw capability TLV: It is requested to be assigned by the
   IANA.

   P-bit:set "1" to indicate whether the node supports the positive MAC
   withdraw capability.

   N-bit:set "1" to indicate whether the node supports the negative MAC
   withdraw capability.

   Reserved: Reserved for future use.

   MAC Withdraw Capability TLV is advertised to a LDP ICCP peer PE that

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   in the same domain, and this TLV may be carried in an LDP
   Initialization message or LDP Capability message.

5.5.2.  Optimized MAC Withdraw processing

   After receiving the MAC withdraw capability through MAC Withdraw
   capability TLV, the PE should process as below:
   o  If the former active PE does not support negative MAC withdraw
      capability, and former standby PE support positive MAC withdraw
      capability, former standby PE will send positive to all other PEs
      with positive MAC capability.
   o  If the former active PE support negative MAC withdraw capability,
      the former active PE sends negative to other PEs that have
      negative MAC withdraw capability.  And if the former standby PE
      also support positive MAC withdraw capability, it will send
      positive to other PEs with positive and without negative MAC
      withdraw capability.

6.  Load Balancing

   It is recommended to configure different PW priority values for
   different VPLS instance, then the active PW of different VPLS will be
   running on different PEs, to provide load balancing between the two
   PEs in one domain.

7.  Security Considerations

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

8.  IANA Consideration

   This document creates a new "MAC Withdraw Capability" that is
   requested to be allocated by IANA.

9.  Acknowledgements

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

   Daniel Cohn
   Orckit-Corrigent 
   Email: danielc@orckit.com

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

10.  References

10.1.  Normative references

   [I-D.ietf-pwe3-iccp]
              Martini, L., Salam, S., Sajassi, A., Bocci, M.,
              Matsushima, S., and T. Nadeau, "Inter-Chassis
              Communication Protocol for L2VPN PE Redundancy",
              draft-ietf-pwe3-iccp-05 (work in progress), April 2011.

   [I-D.ietf-pwe3-redundancy-bit]
              Muley, P. and M. Aissaoui, "Pseudowire Preferential
              Forwarding Status Bit", draft-ietf-pwe3-redundancy-bit-07
              (work in progress), May 2012.

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

10.2.  Informative References

   [I-D.ietf-l2vpn-vpls-ldp-mac-opt]
              Dutta, P., Balus, F., Stokes, O., and G. Calvignac, "LDP
              Extensions for Optimized MAC Address Withdrawal in
              H-VPLS", draft-ietf-l2vpn-vpls-ldp-mac-opt-06 (work in
              progress), May 2012.

   [I-D.ietf-l2vpn-vpls-mcast]
              Aggarwal, R., Rekhter, Y., Kamite, Y., and L. Fang,
              "Multicast in VPLS", draft-ietf-l2vpn-vpls-mcast-10 (work
              in progress), February 2012.

   [I-D.ietf-pwe3-redundancy]
              Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire
              Redundancy", draft-ietf-pwe3-redundancy-08 (work in
              progress), May 2012.

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

   [RFC5561]  Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
              Le Roux, "LDP Capabilities", RFC 5561, July 2009.

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Authors' Addresses

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

   Email: zhliu@gsta.com

   Lizhong Jin
   ZTE Corporation
   889 Bibo Road
   Shanghai 201203
   P.R.China

   Email: lizhong.jin@zte.com.cn

   Ran Chen
   ZTE Corporation
   68 Zijinghua Road
   Nanjing 210012
   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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