Networking Working Group                                          Z. Liu
Internet-Draft                                             China Telecom
Intended status: Standards Track                                  L. Jin
Expires: October 12, 2014
                                                                 R. Chen
                                                         ZTE Corporation
                                                                  D. Cai
                                                                S. Salam
                                                                   Cisco
                                                          April 10, 2014


             Redundancy provisioning for VPLS Inter-domain
            draft-ietf-l2vpn-vpls-inter-domain-redundancy-05

Abstract

   In many existing Virtual Private LAN Service (VPLS) deployments 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 domains.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 12, 2014.

Copyright Notice

   Copyright (c) 2014 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



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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


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 . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     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  . . . . . . . . . .  7
   6.  Management Considerations  . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Consideration . . . . . . . . . . . . . . . . . . . . . .  9
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . .  9
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     11.1. Normative references . . . . . . . . . . . . . . . . . . . 10
     11.2. Informative references . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11




















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1.  Introduction

   In many existing Virtual Private LAN Service (VPLS) deployments based
   on [RFC4762], inter-domain connectivity has been deployed without
   node redundancy, or with node redundancy in a single domain.  This
   document is to provide a service protection mechanism for inter-
   domain VPLS based on [RFC4762].  The protection mechanism will
   provide edge node redundancy and link redundancy in both domains.
   The domain in this document refers to autonomous system (AS), or
   other administrative domains.

   The solution relies on the use of ICCP [I-D.ietf-pwe3-iccp] to
   coordinate between redundant edge nodes, and use of Pseudowire (PW)
   Preferential Forwarding Status Bit [RFC6870] to negotiate the PW
   status.  There is no change to any protocol message formats and no
   new protocol options introduced.  This solution is a description of
   reusing existing protocol building blocks to achieve the desired
   function, but also defines implementation behaviour necessary for the
   function to work.


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 like
   Inter-AS option A in [RFC4364] section 10, 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 interconnection: 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 aggregated.
   These two conditions cannot always be guaranteed in live deployments.
   For instance, there are many scenarios where the interconnect between
   the domains uses Packet over Sonet/SDH (POS), thereby ruling out the



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   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
   described in this document 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 [RFC7117], the solution described here provides a
   better behavior compared to inter-AS option B: with option B, each
   Provider Edge (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 Autonomous
   System Border Router (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.  The master/slave mode
   provides some enhanced capabilities and, hence, is included in this
   document.


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.  PE3 and PE4 belong to one redundancy group (RG),
   and PE5 and PE6 belong to another RG.  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.





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



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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
   the two ICCP peers in the same RG.  One method to ensure mode
   consistency is by manual operation.  Other methods are also possible
   and are out of the scope of this document.

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 should negotiate to



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   configure the same PW high/low priority at two PW end-points.  The
   inter-domain VPLS relationship normally involves a contractual
   process between operators, and the configuration of PW roles forms
   part of this process.  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 two options to provide protection: 1:1
   and 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 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 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 5.1.1.

   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 status bit [RFC6870] 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



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      synchronize the latest PW status on both PE sides;
   o  While waiting for the acknowledgement, 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
   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.  Management Considerations

   When deploying the inter-domain redundancy mechanism described in
   this document, some manual operation/negotiation is required to be
   done correctly and securely.  E.g., each node within one RG should be
   configured with same redundancy mode; the two operators should



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   negotiate to configure same PW priority at two nodes.  If the
   configuration consistency is broken, the inter-domain redundancy
   mechanism may not work properly.


7.  Security Considerations

   Besides the security properties of [I-D.ietf-pwe3-iccp], [RFC4762]
   and [RFC6870], this document will have additional security
   consideration.

   ICCP is now deployed between two PEs or ASBRs, the two PEs or ASBRs
   should be connected by a well managed and highly monitored network.
   The LDP session could be secured with TCP Authentication Option
   [RFC5925].  This provides integrity and authentication for the ICCP
   messages.  The LDP MD5 authentication key option, as described in
   section 2.9 of [RFC5036] MAY also be used.

   The attention of implementers and deployers is drawn to [RFC6941] and
   [RFC6952] with special attention to the recommendation to use TCP-AO
   [RFC5925] for enhanced security of LDP sessions.

   The activitiy on the inter-domain and intra-domain pseudowire may
   cause security threats or be exploited to create denial of service
   attackes.  Excessive pseudowire state flapping (e.g., by malicious
   peer PE's implementation) may lead to excessive ICCP exchanges.
   Implementations SHOULD provide mechanisms to perform control-plane
   policing and mitigate such types of attacks.


8.  IANA Consideration

   No IANA allocation is required in this document.


9.  Acknowledgements

   The author would like to thank Sami Boutros, Giles Heron for their
   valuable comments.


10.  Contributors

      Daniel Cohn

      Email:daniel.cohn.ietf@gmail.com





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


11.  References

11.1.  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-16 (work in progress),
              March 2014.

   [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.

11.2.  Informative references

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, February 2006.

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

   [RFC5036]  Andersson, L., Minei, I., and B. Thomas, "LDP
              Specification", RFC 5036, October 2007.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, June 2010.

   [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.

   [RFC6941]  Fang, L., Niven-Jenkins, B., Mansfield, S., and R.
              Graveman, "MPLS Transport Profile (MPLS-TP) Security
              Framework", RFC 6941, April 2013.



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   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, May 2013.

   [RFC7117]  Aggarwal, R., Kamite, Y., Fang, L., Rekhter, Y., and C.
              Kodeboniya, "Multicast in Virtual Private LAN Service
              (VPLS)", RFC 7117, February 2014.


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







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

   Email: ssalam@cisco.com












































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