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Versions: (draft-ietf-pwe3-redundancy-spe) 00 01 02 03 RFC 7795

Network Working Group                                            J. Dong
Internet-Draft                                                   H. Wang
Intended status: Standards Track                     Huawei Technologies
Expires: May 19, 2016                                  November 16, 2015


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

Abstract

   This document describes Multi-Segment Pseudowire (MS-PW) protection
   scenarios in which the pseudowire redundancy is provided on the
   Switching Provider Edge (S-PE) defined in RFC 5659.  Operations of
   the S-PEs which provide PW redundancy are specified in this document.
   Signaling of the Preferential Forwarding status as defined in RFC
   6870 and RFC 6478 is reused.  This document does not require any
   change to the Terminating Provider Edges (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
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   This Internet-Draft will expire on May 19, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Typical Scenarios of PW Redundancy on S-PE  . . . . . . . . .   3
     2.1.  MS-PW Redundancy on S-PE  . . . . . . . . . . . . . . . .   3
     2.2.  MS-PW Redundancy on S-PE with S-PE Protection . . . . . .   4
   3.  S-PE Operations . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Applications of PW Redundancy on S-PE . . . . . . . . . . . .   5
     4.1.  Applications in Scenario 1  . . . . . . . . . . . . . . .   5
     4.2.  Applications in Scenario 2  . . . . . . . . . . . . . . .   6
   5.  VCCV Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

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 are 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 of providing PW
   redundancy on Switching Provider Edge (S-PEs), such as reducing the
   burden on the access T-PE nodes, and enabling faster protection
   switching compared to the end-to-end MS-PW protection mechanisms.

   This document describes some scenarios in which PW redundancy is
   provided on S-PEs, and specifies the operations of the S-PEs.  The
   S-PEs connect to the neighboring T-PEs or S-PEs with PW segments.
   For the S-PE which provides PW redundancy for MS-PW, there is a
   single PW segment on one side, which is called the single-homed side,



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   and on the other side there are multiple PW segments, which is called
   the multi-homed side.  The scenario in which the S-PE has two multi-
   homed sides is out of scope.  Signaling of the preferential
   forwarding status as defined in [RFC6870] and [RFC6478] 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 of providing
   PW redundancy on S-PEs.  This section describes typical scenarios of
   PW redundancy on S-PE.

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, Customer Edge (CE) node 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 segments PW-Seg2 and
   PW-Seg3 provide resiliency on S-PE1 for the failure of T-PE2, T-PE3
   or the connected Attachment Circuits (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 support PW redundancy.
   Besides, 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 end-to-end MS-PW redundancy is used.  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.








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

         +---+    +-----+      +-----+           +-----+
         |   |    |     |      |     |           |     |
         |   |    |......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 both 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 MS-PW, and PW1-Seg2 between S-PE1 and T-PE2 is the primary PW
   segment.  MS-PW2 is the secondary MS-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.  Note that when PW redundancy for MS-PW
   is provided on S-PE, the optional S-PE Bypass Mode as defined in
   [RFC6478] MUST NOT be used, otherwise the S-PE will not receive the



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   PW status messages originated by T-PEs.  This section specifies the
   operations of S-PEs on which PW redundancy is provisioned.  This
   section does not make any change to the T-PEs of MS-PW.

   The S-PEs connect to the neighboring T-PEs or other S-PEs on two
   sides with PW segments.  For the S-PE which provides PW redundancy
   for an MS-PW, on one side there is a single PW segment, which is
   called the single-homed side, and on the other side there are
   multiple PW segments, which is called the multi-homed side.  The
   scenario in which the S-PE has two multi-homed sides is out of scope.

   The S-PE which provides PW redundncy MUST work as a Slave node for
   the single-homed side, and MUST work in Independent mode for the
   multi-homed side.  Consequently, The T-PE on the single-homed side
   MUST work in the Master mode, and the T-PEs on the multi-homed side
   MUST work in the Independent mode.  The Signaling of the Preferential
   Forwarding bit as defined in [RFC6870] and [RFC6478] is reused.

   The S-PE MUST pass the Preferential Forwarding status received from
   the single-homed side unchanged to all the PW segments on the multi-
   homed side.  The S-PE MUST advertise the Standby Preferential
   Forwarding status to the single-homed side if it receives Standby
   status from all the PW segments on the multi-homed side, and it MUST
   advertise the Active Preferential Forwarding status to the single-
   homed side if it receives Active status from any of the PW segments
   on the multi-homed side.  For the single-homed side, the active PW
   segment is determined by the T-PE on this side, which works as the
   Master node.  On the multi-homed side, since both the S-PE and T-PEs
   work in the Independent mode, the PW segment which has both local and
   remote Up/Down status and Preferential Forwarding status as Up and
   Active MUST be selected for traffic forwarding.  When a switchover
   happens on the S-PE, if the S-PE supports the SP-PE TLV processing as
   defined in [RFC6073], it SHOULD advertise the updated SP-PE TLVs by
   sending a Label Mapping message to the T-PEs.

4.  Applications of PW Redundancy on S-PE

4.1.  Applications in 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 the Active
   Preferential Forwarding status bit on the single-homed side from
   T-PE1, then it would advertise the Active Preferential Forwarding
   status bit on both PW-Seg2 and PW-Seg3.  T-PE2 and T-PE3 would
   advertise the Active and Standby Preferential Forwarding status bit
   to S-PE1 respectively, reflecting the forwarding state of the two ACs
   connected to CE2.  By matching the local and remote Up/Down status




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   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 the Active
   Preferential Forwarding 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 the 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-homed side, it will not
   advertise any change of the PW status to T-PE1.  If S-PE1 supports
   the SP-PE TLV processing as defined in [RFC6073], it would advertise
   the updated SP-PE TLVs by sending a Label Mapping message to T-PE1.

4.2.  Applications in 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 the Active
   and Standby Preferential Forwarding status bit to S-PE1 and S-PE2
   respectively according to configuration.  According to the received
   Preferential Forwarding status bit, S-PE1 would advertise the Active
   Preferential Forwarding status bit to both T-PE2 and T-PE3, and S-PE2
   would advertise the Standby Preferential Forwarding status bit to
   both T-PE2 and T-PE3.  T-PE2 would advertise the Active Preferential
   Forwarding status bit to both S-PE1 and S-PE2, and T-PE3 would
   advertise the Standby Preferential Forwarding status bit to both
   S-PE1 and S-PE2, reflecting the forwarding state of the two ACs
   connected 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-homed side, it would advertise the
   Active Preferential Forwarding status bit to T-PE1, and S-PE2 would
   advertise the Standby Preferential Forwarding status bit to T-PE1
   since it does not have any Active PW segment on the multi-homed 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 the
   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 the status of
   "Pseudowire forwarding", and select PW1-Seg3 for traffic forwarding.
   Since S-PE1 still has an Active PW segment on the multi-homed side,
   it would not advertise any change of the PW status to T-PE1.  If
   S-PE1 supports the SP-PE TLV processing as defined in [RFC6073], it



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   would advertise the updated SP-PE TLVs by sending a Label Mapping
   message to T-PE1.

   If S-PE1 fails, T-PE1 would notice this through some 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 detection mechanism.  Then
   by matching the local and remote Up/Down and Preferential Forwarding
   status, PW2-Seg2 would be selected for traffic forwarding.

5.  VCCV Considerations

   For PW Virtual Circuit Connectivity Verification (VCCV) [RFC5085],
   the Control Channel (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 PW label TTL MUST be set to the
   appropriate value to reach the target PE.  The hop count from one
   T-PE to the target PE can be obtained either via SP-PE TLVs, through
   MS-PW path trace or based on management plane information.

6.  IANA Considerations

   This document makes no request of IANA.

7.  Security Considerations

   Since PW redundancy is provided on the S-PE nodes of MS-PWs, it is
   important that the security mechanisms as defined in [RFC4447],
   [RFC6073] and [RFC6478] are implemented to ensure that the S-PE nodes
   and the messages sent and received by the S-PE nodes are not
   compromised.

8.  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.

9.  References








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9.1.  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>.

   [RFC4447]  Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
              G. Heron, "Pseudowire Setup and Maintenance Using the
              Label Distribution Protocol (LDP)", RFC 4447,
              DOI 10.17487/RFC4447, April 2006,
              <http://www.rfc-editor.org/info/rfc4447>.

   [RFC6073]  Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
              Aissaoui, "Segmented Pseudowire", RFC 6073,
              DOI 10.17487/RFC6073, January 2011,
              <http://www.rfc-editor.org/info/rfc6073>.

   [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>.

9.2.  Informative References

   [RFC3985]  Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
              Edge-to-Edge (PWE3) Architecture", RFC 3985,
              DOI 10.17487/RFC3985, March 2005,
              <http://www.rfc-editor.org/info/rfc3985>.

   [RFC5085]  Nadeau, T., Ed. and C. Pignataro, Ed., "Pseudowire Virtual
              Circuit Connectivity Verification (VCCV): A Control
              Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085,
              December 2007, <http://www.rfc-editor.org/info/rfc5085>.

   [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>.

   [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>.



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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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