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Versions: 00 01 02 draft-ietf-pals-ms-pw-protection

Network Working Group                                           A. Malis
Internet-Draft                                              L. Andersson
Updates: 6870 (if approved)                 Huawei Technologies Co., Ltd
Intended status: Standards Track                         H. van Helvoort
Expires: April 13, 2015                                   Hai Gaoming BV
                                                                 J. Shin
                                                              SK Telecom
                                                                 L. Wang
                                                            China Mobile
                                                         A. D'Alessandro
                                                          Telecom Italia
                                                        October 10, 2014


      S-PE Outage Protection for Static Multi-Segment Pseudowires
               draft-shawam-pwe3-ms-pw-protection-02.txt

Abstract

   In MPLS and MPLS-TP environments, statically provisioned Single-
   Segment Pseudowires (SS-PWs) are protected against tunnel failure via
   MPLS-level and MPLS-TP-level tunnel protection.  With statically
   provisioned Multi-Segment Pseudowires (MS-PWs), each segment of the
   MS-PW is likewise protected from tunnel failures via MPLS-level and
   MPLS-TP-level tunnel protection.  However, static MS-PWs are not
   protected end-to-end against failure of one of the switching PEs
   (S-PEs) along the path of the MS-PW.  This document describes how to
   achieve this protection by updating the existing procedures in RFC
   6870.  It also contains an optional approach based on MPLS-TP Linear
   Protection.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 April 13, 2015.




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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
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Extension to RFC 6870 to Protect Statically Provisioned SS-
       PWs and MS-PWs  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Operational Considerations  . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Optional Linear Protection Approach  . . . . . . . .   6
     A.1.  Introduction  . . . . . . . . . . . . . . . . . . . . . .   6
     A.2.  Encapsulation of the PSC Protocol for Pseudowires . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   As described in RFC 5659 [RFC5659], Multi-Segment Pseudowires (MS-
   PWs) consist of terminating PEs (T-PEs), switching PEs (S-PEs), and
   PW segments between the T-PEs at each of the MS-PW and the interior
   S-PEs.  In MPLS and MPLS-TP environments, statically provisioned
   Single-Segment Pseudowires (SS-PWs) are protected against tunnel
   failure via MPLS-level and MPLS-TP-level tunnel protection.  With
   statically provisioned Multi-Segment Pseudowires (MS-PWs), each PW
   segment of the MS-PW is likewise protected from tunnel failure via
   MPLS-level and MPLS-TP-level tunnel protection.  However, PSN tunnel
   protection does not protect static MS-PWs from failures of S-PEs
   along the path of the MS-PW.





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   RFC 6718 [RFC6718] provides a general framework for PW protection,
   and RFC 6870 [RFC6870], which is based upon that framework, describes
   protection procedures for MS-PWs that are dynamically signaled using
   LDP.  This document describes how to achieve protection against S-PE
   failure in a static MS-PW by extending RFC 6870 to be applicable for
   statically provisioned MS-PWs pseudowires (PWs) as well.

   This document also contains an optional alternative approach based on
   MPLS-TP Linear Protection.  This approach, described in Appendix A,
   MUST be identically provisioned in the PE endpoints for the protected
   MS-PW in order to be used.  See Appendix A for further details on
   this alternative approach.

1.1.  Requirements Language

   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].

2.  Extension to RFC 6870 to Protect Statically Provisioned SS-PWs and
    MS-PWs

   Section 3.2.3 of RFC 6718 and Section A.5 of RFC 6870 document how to
   use redundant MS-PWs to protect an MS-PW against S-PE failure in the
   case of a singly-homed CE, using the following network model from RFC
   6718:

























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       Native   |<----------- Pseudowires ----------->|  Native
       Service  |                                     |  Service
        (AC)    |     |<-PSN1-->|     |<-PSN2-->|     |  (AC)
          |     V     V         V     V         V     V   |
          |     +-----+         +-----+         +-----+   |
   +----+ |     |T-PE1|=========|S-PE1|=========|T-PE2|   |   +----+
   |    |-------|......PW1-Seg1.......|.PW1-Seg2......|-------|    |
   | CE1|       |     |=========|     |=========|     |       | CE2|
   |    |       +-----+         +-----+         +-----+       |    |
   +----+        |.||.|                          |.||.|       +----+
                 |.||.|         +-----+          |.||.|
                 |.||.|=========|     |========== .||.|
                 |.||...PW2-Seg1......|.PW2-Seg2...||.|
                 |.| ===========|S-PE2|============ |.|
                 |.|            +-----+             |.|
                 |.|============+-----+============= .|
                 |.....PW3-Seg1.|     | PW3-Seg2......|
                  ==============|S-PE3|===============
                                |     |
                                +-----+

              Figure 1: Single-Homed CE with Redundant MS-PWs

   In this figure, CE1 is connected to PE1 and CE2 is connected to PE2.
   There are three MS PWs.  PW1 is switched at S-PE1, PW2 is switched at
   S-PE2, and PW3 is switched at S-PE3.  This scenario provides N:1
   protection against S-PE failure for the subset of the path of the
   emulated service from T-PE1 to T-PE2.

   The procedures in RFCs 6718 and 6870 rely on LDP-based PW status
   signaling to signal the state of the primary MS-PW that is being
   protected, and the precedence in which redundant MS-PW(s) should be
   used to protect the primary MS-PW should it fail.  These procedures
   make use of information carried by the PW Status TLV, which for
   dynamically signaled PWs is carried by the LDP protocol.

   However, statically provisioned PWs (SS-PWs or MS-PWs) do not use the
   LDP protocol for PW set and signaling, rather they are provisioned by
   network management systems or other means at each T-PE and S-PE along
   their path.  They also do not use the LDP protocol for status
   signaling.  Rather, they use procedures defined in RFC 6478 [RFC6478]
   for status signaling via the PW OAM message using the PW Associated
   Channel Header (ACH).  The PW Status TLV carried via this status
   signaling is itself identical to the PW Status TLV carried via LDP-
   based status signaling, including the identical PW Status Codes.

   Sections 6 and 7 of RFC 6870 describes the management of a primary PW
   and its secondary PW(s) to provide resiliency to the failure of the



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   primary PW.  They use status codes transmitted between endpoint T-PEs
   using the PW Status TLV transmitted by LDP.  For this management to
   apply to statically provisioned PWs, the PW status signaling defined
   in RFC 6478 MUST be used for the primary and secondary PWs.  In that
   case, the endpoint T-PEs can then use the PW status signaling
   provided by RFC 6478 in the place of LDP-based status signaling, but
   otherwise operate identically as described in RFC 6870.

3.  Operational Considerations

   Because LDP is not used between the T-PEs for statically provisioned
   MS-PWs, the negotiation procedures described in RFC 6870 cannot be
   used.  Thus, operational care must be taken so that the endpoint
   T-PEs are identically provisioned regarding the use of this document,
   specifically whether or not MS-PW redundancy is being used, and for
   each protected MS-PW, the identity of the primary MS-PW and the
   precedence of the secondary MS-PWs.

4.  Security Considerations

   The security considerations defined for RFC 6478 apply to this
   document as well.  As the security considerations in RFCs 6718 and
   6870 are related to their use of LDP, they are not required for this
   document.

   If the alternative approach in Appendix A is used, then the security
   considerations defined for RFCs 6378, 7271, and 7324 also apply.

5.  IANA Considerations

   There are no requests for IANA actions in this document.

   Note to the RFC Editor - this section can be removed before
   publication.

6.  Acknowledgements

   The authors would like to thank Matthew Bocci, Yaakov Stein, and
   David Sinicrope for their comments on this document.

   Figure 1 and the explanatory paragraph following the figure were
   taken from RFC 6718.

7.  References







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7.1.  Normative References

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

   [RFC6378]  Weingarten, Y., Bryant, S., Osborne, E., Sprecher, N., and
              A. Fulignoli, "MPLS Transport Profile (MPLS-TP) Linear
              Protection", RFC 6378, October 2011.

   [RFC6478]  Martini, L., Swallow, G., Heron, G., and M. Bocci,
              "Pseudowire Status for Static Pseudowires", RFC 6478, May
              2012.

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

   [RFC7271]  Ryoo, J., Gray, E., van Helvoort, H., D'Alessandro, A.,
              Cheung, T., and E. Osborne, "MPLS Transport Profile (MPLS-
              TP) Linear Protection to Match the Operational
              Expectations of Synchronous Digital Hierarchy, Optical
              Transport Network, and Ethernet Transport Network
              Operators", RFC 7271, June 2014.

   [RFC7324]  Osborne, E., "Updates to MPLS Transport Profile Linear
              Protection", RFC 7324, July 2014.

7.2.  Informative References

   [RFC5659]  Bocci, M. and S. Bryant, "An Architecture for Multi-
              Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
              October 2009.

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

Appendix A.  Optional Linear Protection Approach

A.1.  Introduction

   In "MPLS Transport Profile (MPLS-TP) Linear Protection" [RFC6378], as
   well as in the later updates of this RFC in "MPLS Transport Profile
   (MPLS-TP) Linear Protection to Match the Operational Expectations of
   SDH, OTN and Ethernet Transport Network Operators" [RFC7271] and in
   "Updates to MPLS Transport Profile Linear Protection" [RFC7324], the
   Protection State Coordination (PSC) protocol was defined for MPLS
   LSPs only.





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   This Appendix extends these RFCs to be applicable for PWs (SS-PW and
   MS-PW) as well.  This is useful especially in the case of end-to-end
   static provisioned MS-PWs running over MPLS-TP where tunnel
   protection alone cannot be relied upon for end-to-end protection of
   PWs against S-PE failure.  It also enables a uniform operational
   approach for protection at LSP and PW layers and an easier management
   integration for networks that already use RFCs 6378, 7271, and 7324.

   This Appendix is optional alternative approach to the one in
   Section 2, therefore all implementations MUST include the approach in
   Section 2 even if this alternative approach is used.  The operational
   considerations in Section 3 continue to apply when this approach is
   used, and operational care must be taken so that the endpoint T-PEs
   are identically provisioned regarding the use of this document.

A.2.  Encapsulation of the PSC Protocol for Pseudowires

   The PSC protocol can be used to protect against defects on any LSP
   (segment, link or path).  In the case of MS-PW, the PSC protocol can
   also protect failed intermediate nodes (S-PE).  Linear protection
   protects an LSP or PW end-to-end and if a failure is detected,
   switches traffic over to another (redundant) set of resources.

   Obviously, the protected entity does not need to be of the same type
   as the protecting.  For example, it is possible to protect a link by
   a path.  Likewise it is possible to protect a SS-PW with a MS-PW and
   vice versa.

   From a PSC protocol point of view it is possible to view a SS-PW as a
   single hop LSP, and a MS-PW as a multiple hop LSP.  Thus, this
   provides end-to-end protection for the SS-PW or MS-PW.  The G-ACh
   carrying the PSC protocol information is placed in the label stack
   directly beneath the PW identifier.  The PSC protocol will then work
   as specified in RFCs 6378, 7271, and 7324.

Authors' Addresses

   Andrew G. Malis
   Huawei Technologies Co., Ltd

   Email: agmalis@gmail.com


   Loa Andersson
   Huawei Technologies Co., Ltd

   Email: loa@mail01.huawei.com




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   Huub van Helvoort
   Hai Gaoming BV

   Email: huubatwork@gmail.com


   Jongyoon Shin
   SK Telecom

   Email: jongyoon.shin@sk.com


   Lei Wang
   China Mobile

   Email: wangleiyj@chinamobile.com


   Alessandro D'Alessandro
   Telecom Italia

   Email: alessandro.dalessandro@telecomitalia.it





























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