S-PE Protection for MPLS and MPLS-TP Static Multi-Segment Pseudowires
draft-ietf-pals-ms-pw-protection-03

Network Working Group                                      A. Malis, Ed.
Internet-Draft                                              L. Andersson
Updates: 6870 (if approved)                 Huawei Technologies Co., Ltd
Intended status: Standards Track                         H. van Helvoort
Expires: April 3, 2016                                    Hai Gaoming BV
                                                                 J. Shin
                                                              SK Telecom
                                                                 L. Wang
                                                            China Mobile
                                                         A. D'Alessandro
                                                          Telecom Italia
                                                         October 1, 2015

 S-PE Protection for MPLS and MPLS-TP Static Multi-Segment Pseudowires
                draft-ietf-pals-ms-pw-protection-03.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 via redundant MS-PWs by updating the existing
   procedures in RFC 6870.  It also contains an optional approach based
   on MPLS-TP Linear Protection.

Status of This Memo

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   This Internet-Draft will expire on April 3, 2016.

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Copyright Notice

   Copyright (c) 2015 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
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   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  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Optional Linear Protection Approach  . . . . . . . .   7
     A.1.  Introduction  . . . . . . . . . . . . . . . . . . . . . .   7
     A.2.  Encapsulation of the PSC Protocol for Pseudowires . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   As described in RFC 5659 [RFC5659], Multi-Segment Pseudowires (MS-
   PWs) consist of terminating PEs (T-PEs), one or more switching PEs
   (S-PEs), and a sequence of PW segments that connects one of the T-PEs
   with its "adjacent" S-PE, connects this S-PE with the next S-PE in
   the sequence and so on until the last S-PE is connected by the last
   PW segment to the remaining T-PE.  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.

   This document differs from [I-D.ietf-pals-redundancy-spe] in that
   this draft provides end-to-end resiliency for static MS-PWs, while
   [I-D.ietf-pals-redundancy-spe] provides resiliency at intermediate
   S-PEs, rather than end-to-end resiliency, and for both dynamically
   signaled and static MS-PWs.

   L2TPv3-based PWs are outside the scope of this document.

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.  Note that
   the optional S-PE Bypass Mode defined in Section 5.5 of RFC 6478
   cannot be used, as it requires LDP signaling.

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, David
   Sinicrope, Sasha Vainshtein, and Italo Busi for their comments on
   this document.

   Figure 1 and the explanatory paragraph following the figure were
   taken from RFC 6718.  Figure 2 was adapted from RFC 6378.

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7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC6378]  Weingarten, Y., Ed., Bryant, S., Osborne, E., Sprecher,
              N., and A. Fulignoli, Ed., "MPLS Transport Profile (MPLS-
              TP) Linear Protection", RFC 6378, DOI 10.17487/RFC6378,
              October 2011, <http://www.rfc-editor.org/info/rfc6378>.

   [RFC6478]  Martini, L., Swallow, G., Heron, G., and M. Bocci,
              "Pseudowire Status for Static Pseudowires", RFC 6478,
              DOI 10.17487/RFC6478, May 2012,
              <http://www.rfc-editor.org/info/rfc6478>.

   [RFC6870]  Muley, P., Ed. and M. Aissaoui, Ed., "Pseudowire
              Preferential Forwarding Status Bit", RFC 6870,
              DOI 10.17487/RFC6870, February 2013,
              <http://www.rfc-editor.org/info/rfc6870>.

   [RFC7271]  Ryoo, J., Ed., Gray, E., Ed., 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, DOI 10.17487/RFC7271, June 2014,
              <http://www.rfc-editor.org/info/rfc7271>.

   [RFC7324]  Osborne, E., "Updates to MPLS Transport Profile Linear
              Protection", RFC 7324, DOI 10.17487/RFC7324, July 2014,
              <http://www.rfc-editor.org/info/rfc7324>.

7.2.  Informative References

   [I-D.ietf-pals-redundancy-spe]
              Dong, J. and H. Wang, "Pseudowire Redundancy on S-PE",
              draft-ietf-pals-redundancy-spe-02 (work in progress),
              August 2015.

   [RFC5659]  Bocci, M. and S. Bryant, "An Architecture for Multi-
              Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
              DOI 10.17487/RFC5659, October 2009,
              <http://www.rfc-editor.org/info/rfc5659>.

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   [RFC6718]  Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire
              Redundancy", RFC 6718, DOI 10.17487/RFC6718, August 2012,
              <http://www.rfc-editor.org/info/rfc6718>.

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.

   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.

   The protection architectures are those defined in [RFC6378].  For the
   purposes of this Appendix, we define the protection domain of a
   point-to-point PW as consisting of two terminating PEs (T-PEs) and
   the transport paths that connect them (see Figure 2).

                 +-----+ //=======================\\ +-----+
                 |T-PE1|//     Working Path        \\|T-PE2|
                 |    /|                             |\    |
                 |  ?< |                             | >?  |
                 |    \|\\    Protection Path      //|/    |
                 +-----+ \\=======================// +-----+

                     |<-------Protection Domain------->|

                        Figure 2: Protection Domain

   This Appendix is an OPTIONAL alternative approach to the one in
   Section 2.  For interoperability, 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.

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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 (editor)
   Huawei Technologies Co., Ltd

   Email: agmalis@gmail.com

   Loa Andersson
   Huawei Technologies Co., Ltd

   Email: loa@mail01.huawei.com

   Huub van Helvoort
   Hai Gaoming BV

   Email: huubatwork@gmail.com

   Jongyoon Shin
   SK Telecom

   Email: jongyoon.shin@sk.com

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   Lei Wang
   China Mobile

   Email: wangleiyj@chinamobile.com

   Alessandro D'Alessandro
   Telecom Italia

   Email: alessandro.dalessandro@telecomitalia.it

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