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Versions: (draft-dong-pwe3-redundancy-spe) 00 01 02 03 draft-ietf-pals-redundancy-spe

Network Working Group                                            J. Dong
Internet-Draft                                                   H. Wang
Intended status: Standards Track                     Huawei Technologies
Expires: May 14, 2015                                  November 10, 2014


                     Pseudowire Redundancy on S-PE
                   draft-ietf-pwe3-redundancy-spe-03

Abstract

   This document describes Multi-Segment Pseudowire (MS-PW) protection
   scenarios in which the pseudowire redundancy is provided on the
   Switching-PE (S-PE).  Operations of the S-PEs which provide PW
   redundancy are specified in this document.  Signaling of the
   preferential forwarding status as defined in [RFC6870] is reused.
   This document does not require any change to the T-PEs of MS-PW.

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].

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 14, 2015.

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



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Typical Scenarios of PW Redundancy on S-PE  . . . . . . . . .   2
     2.1.  MS-PW Redundancy on S-PE  . . . . . . . . . . . . . . . .   3
     2.2.  MS-PW Redundancy on S-PE with S-PE Protection . . . . . .   3
   3.  S-PE Operations . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Operations of Scenario 1  . . . . . . . . . . . . . . . .   5
     3.2.  Operations of Scenario 2  . . . . . . . . . . . . . . . .   5
   4.  VCCV Considerations . . . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   [RFC6718] describes the framework and requirements for pseudowire
   (PW) redundancy, and [RFC6870] specifies Pseudowire (PW) redundancy
   mechanism for scenarios where a set of redundant PWs is configured
   between provider edge (PE) nodes in single-segment pseudowire (SS-PW)
   [RFC3985]applications, or between terminating provider edge (T-PE)
   nodes in multi-segment pseudowire (MS-PW) [RFC5659] applications.

   In some MS-PW scenarios, there are benefits to provide PW redundancy
   on S-PEs, such as reducing the burden on the access T-PE nodes, and
   faster protection switching.  This document describes some scenarios
   in which PW redundancy is provided on S-PEs, and specifies the
   operations of the S-PEs.  Signaling of the preferential forwarding
   status as defined in [RFC6870] is reused.  This document does not
   require any change to the T-PEs of MS-PW.

2.  Typical Scenarios of PW Redundancy on S-PE

   In some MS-PW deployment scenarios, there are benefits to provide PW
   redundancy on S-PEs.  This section describes typical scenarios of PW
   redundancy on S-PE.



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2.1.  MS-PW Redundancy on S-PE

                                              +-----+
            +---+                 +-----+      |     |    +---+
            |   |                 |     |------|T-PE2|----|   |
            |   |    +-----+      |  ..PW-Seg2.......|    |   |
            |   |    |....PW-Seg1.....  |      +-----+    |   |
            |CE1|----|T-PE1|------|S-PE1|                 |CE2|
            |   |    |     |      |  .  |      +-----+    |   |
            |   |    +-----+      |  ..PW-Seg3.......|    |   |
            |   |                 |     |------|T-PE3|----|   |
            +---+                 +-----+      |     |    +---+
                                               +-----+
                       Figure 1.MS-PW Redundancy on S-PE

   As illustrated in Figure 1, CE1 is connected to T-PE1 while CE2 is
   dual-homed to T-PE2 and T-PE3.  T-PE1 is connected to S-PE1 only, and
   S-PE1 is connected to both T-PE2 and T-PE3.  The MS-PW is switched on
   S-PE1, and PW-Seg2 and PW-Seg3 provides resiliency on S-PE1 for
   failure of T-PE2 or T-PE3 or the connected ACs.  PW-Seg2 is selected
   as the primary PW segment, and PW-Seg3 is the secondary PW segment.

   MS-PW redundancy on S-PE is beneficial for the scenario in Figure 1
   since T-PE1 as an access node may not be able to provide PW
   redundancy, especially when the PW-Seg1 between T-PE1 and S-PE1 is
   statically configured.  And with PW redundancy on S-PE, the number of
   PW segments required between T-PE1 and S-PE1 is only half of the
   number of PW segments needed when using end-to-end MS-PW redundancy.
   In addition, in this scenario PW redundancy on S-PE could provide
   faster protection switching, compared with end-to-end protection
   switching of MS-PW.

2.2.  MS-PW Redundancy on S-PE with S-PE Protection


















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         +---+    +-----+      +-----+           +-----+
         |   |    |     |      |     |           |     |
         |   |    |......PW1-Seg1......PW1-Seg2........|
         |   |    |   .           .  |           |     |
         |CE1|----|T-PE1|------|S-PE1|-----------|T-PE2|
         |   |    |   . |      |  .  | PW1-Seg3  |     |    +---+
         |   |    +   . +      |  .........      ......|----|   |
         |   |    |   . |      |     |    .     .|     |    |   |
         +---+    +---.-+      +-----+     .   . +-----+    |   |
                     |.                     . .             |CE2|
                     |.                      ..             |   |
                     |.        +-----+      .  . +-----+    |   |
                     |.        |     |     .    .|     |----|   |
                     |...PW2-Seg1..........      ......|    +---+
                     |         |  .  | PW2-Seg2  |     |
                     ----------|S-PE2|-----------|T-PE3|
                               |  .  |           |     |
                               |  .....PW2-Seg3........|
                               |     |           |     |
                               +-----+           +-----+
           Figure 2. MS-PW Redundancy on S-PE with S-PE protection

   As illustrated in Figure 2, CE1 is connected to T-PE1 while CE2 is
   dual-homed to T-PE2 and T-PE3.  T-PE1 is connected to S-PE1 and
   S-PE2, and both S-PE1 and S-PE2 are connected to both T-PE2 and
   T-PE3.  There are two MS-PWs which are switched at S-PE1 and S-PE2
   respectively to provide S-PE node protection.  For MS-PW1, S-PE1
   provides resiliency using PW1-Seg2 and PW1-Seg3.  For MS-PW2, S-PE2
   provides resiliency using PW2-Seg2 and PW2-Seg3.  MS-PW1 is the
   primary PW and PW1-Seg2 between S-PE1 and T-PE2 is the primary PW
   segment.  MS-PW2 is the secondary PW.

   MS-PW redundancy on S-PE is beneficial for this scenario since it
   reduces the number of end-to-end MS-PWs required for both T-PE and
   S-PE protection.  In addition, PW redundancy on S-PE could provide
   faster protection switching, compared with end-to-end protection
   switching of MS-PW.

3.  S-PE Operations

   For an S-PE which provides PW redundancy for MS-PW, it is important
   to advertise proper preferential forwarding status to the PW segments
   on both sides and perform protection switching according to the
   received status information.  This section specifies the operations
   of S-PEs on which PW redundancy is provisioned.  This document does
   not make any change to the T-PEs of MS-PW.





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   In general, the S-PE SHOULD work as a Slave node for the single-
   connected side, and SHOULD work in Independent mode for the multi-
   connected side.  The S-PE SHOULD pass the preferential forwarding
   status received from the single-connected side unchanged to the PW
   segments on the multi-connected side.  The S-PE SHOULD advertise
   Standby status to the single-connected side if it receives Standby
   status from all the PW segments on the multi-connected side, and it
   SHOULD advertise Active status to the single-connected side if it
   receives Active status from any of the PW segments on the multi-
   connected side.  For the single-connected side, the active PW segment
   is determined by the T-PE on this side, which works as the Master
   node.  On the multi-connected side, the PW segment which has both
   local and remote Up/Down status and Preferential Forwarding status as
   Up and Active SHOULD be selected for traffic forwarding.

   The Signaling of Preferential Forwarding bit defined in [RFC6870] is
   reused in these scenarios.

3.1.  Operations of Scenario 1

   For the scenario in Figure 1, assume the AC from CE2 to T-PE2 is
   active.  In normal operation, S-PE1 would receive Active Preferential
   Forwarding status bit on the single-connected side from T-PE1, then
   it would advertise Active Preferential Forwarding status bit on both
   PW-Seg2 and PW-Seg3.  T-PE2 and T-PE3 would advertise Active and
   Standby preferential status bit respectively to S-PE1, reflecting the
   forwarding state of the two ACs to CE2.  By matching the local and
   remote Up/Down status and Preferential Forwarding status, PW-Seg2
   would be used for traffic forwarding.

   On failure of the AC between CE2 and T-PE2, the forwarding state of
   AC on T-PE3 is changed to Active.  T-PE3 then advertises Active
   Preferential Status to S-PE1, and T-PE2 would advertise a PW status
   Notification message to S-PE1, indicating that the AC between CE2 and
   T-PE2 is down.  S-PE1 would perform the switchover according to the
   updated local and remote Preferential Forwarding status and status of
   "Pseudowire forwarding", and select PW-Seg3 as the new PW Segment for
   traffic forwarding.  Since S-PE1 still connects to an Active PW
   segment on the multi-connected side, it will not advertise any change
   of the PW status to T-PE1.  S-PE1 may advertise the updated Switching
   Point PE TLVs (SP-PE TLVs) [RFC6073] using Label Mapping message to
   T-PE1.

3.2.  Operations of Scenario 2

   For the scenario of Figure 2, assume the AC from CE2 to T-PE2 is
   active.  T-PE1 works in Master mode and it would advertise Active and
   Standby Preferential Forwarding status bit respectively to S-PE1 and



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   S-PE2 according to configuration.  According to the received
   Preferential Forwarding status bit, S-PE1 would advertise Active
   Preferential Forwarding status bit to both T-PE2 and T-PE3, and S-PE2
   would advertise Standby Preferential Forwarding status bit to both
   T-PE2 and T-PE3.  T-PE2 would advertise Active Preferential
   Forwarding status bit to both S-PE1 and S-PE2, and T-PE3 would
   advertise Standby Preferential Forwarding status bit to both S-PE1
   and S-PE2, reflecting the forwarding state of the two ACs to CE2.  By
   matching the local and remote Up/Down Status and Preferential
   Forwarding status, PW1-Seg2 from S-PE1 to T-PE2 would be used for
   traffic forwarding.  Since S-PE1 connects to the Active PW segment on
   the multi-connected side, it would advertise Active Preferential
   Forwarding status bit to T-PE1, and S-PE2 would advertise Standby
   Preferential Forwarding status bit to T-PE1 since it does not have
   any Active PW segment on the multi-connected side.

   On failure of the AC between CE2 and T-PE2, the forwarding state of
   AC on T-PE3 is changed to Active.  T-PE3 would then advertise Active
   Preferential Forwarding status bit to both S-PE1 and S-PE2, and T-PE2
   would advertise a PW status Notification message to both S-PE1 and
   S-PE2, indicating that the AC between CE2 and T-PE2 is down.  S-PE1
   would perform the switchover according to the updated local and
   remote Preferential Forwarding status and status of "Pseudowire
   forwarding", and select PW1-Seg3 for traffic forwarding.  Since S-PE1
   still has an Active PW segment on the multi-connected side, it would
   not advertise any change of the PW status to T-PE1.  S-PE1 may
   advertise the updated SP-PE TLVs [RFC6073] using Label Mapping
   message to T-PE1.

   If S-PE1 fails, T-PE1 would notice this through some kind of
   detection mechanism and then advertise the Active Preferential
   Forwarding status bit to S-PE2, and PW2-Seg1 would be selected by
   T-PE1 for traffic forwarding.  On receipt of the newly changed
   Preferential Forwarding status, S-PE2 would advertise the Active
   Preferential Forwarding status to both T-PE2 and T-PE3.  T-PE2 and
   T-PE3 would also notice the failure of S-PE1 by some kind of
   detection mechanism.  Then by matching the local and remote Up/Down
   and Preferential Forwarding status, PW2-Seg2 would be selected for
   traffic forwarding.

4.  VCCV Considerations

   PW VCCV [RFC5085] CC type 1 "PW ACH" can be used with S-PE redundancy
   mechanism.  VCCV CC type 2 "Router Alert Label" is not supported for
   MS-PW as specified in [RFC6073].  If VCCV CC type 3 "TTL Expiry" is
   to be used, the hop count from one T-PE to the remote T-PE needs to
   be obtained in advance.  This can be achieved either by control plane
   SP-PE TLVs or through data plane tracing of the MS-PW.



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5.  IANA Considerations

   This document makes no request of IANA.

6.  Security Considerations

   This document has the same security properties as in the PWE3 control
   protocol [RFC4447] and [RFC6870].

7.  Acknowledgements

   The authors would like to thank Mach Chen, Lizhong Jin, Mustapha
   Aissaoui, Luca Martini, Matthew Bocci and Stewart Bryant for their
   valuable comments and discussions.

8.  References

8.1.  Normative References

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

   [RFC4447]  Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
              Heron, "Pseudowire Setup and Maintenance Using the Label
              Distribution Protocol (LDP)", RFC 4447, April 2006.

   [RFC6073]  Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
              Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011.

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

8.2.  Informative References

   [RFC3985]  Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
              Edge (PWE3) Architecture", RFC 3985, March 2005.

   [RFC5085]  Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
              Connectivity Verification (VCCV): A Control Channel for
              Pseudowires", RFC 5085, December 2007.

   [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.




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Authors' Addresses

   Jie Dong
   Huawei Technologies
   Huawei Building, No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: jie.dong@huawei.com


   Haibo Wang
   Huawei Technologies
   Huawei Building, No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: rainsword.wang@huawei.com

































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