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Versions: (draft-cheng-pwe3-mpls-tp-dual-homing-protection) 00 01 02 03 04 05 06 RFC 8184

Network Working Group                                           W. Cheng
Internet-Draft                                                   L. Wang
Intended status: Informational                                     H. Li
Expires: October 28, 2017                                   China Mobile
                                                               S. Davari
                                                    Broadcom Corporation
                                                                 J. Dong
                                                     Huawei Technologies
                                                          April 26, 2017


        Dual-Homing Protection for MPLS and MPLS-TP Pseudowires
           draft-ietf-pals-mpls-tp-dual-homing-protection-06

Abstract

   This document describes a framework and several scenarios for a
   Pseudowire (PW) dual-homing local protection mechanism which avoids
   unnecessary switchovers and which can be used for scenarios using a
   control plane or not using a control plane.  A Dual-Node
   Interconnection (DNI) PW is used for carrying traffic between the
   dual-homing Provider Edge (PE) nodes for carrying traffic when a
   failure occurs in one of the Attachment Circuits (AC) or PWs.  This
   PW dual-homing local protection mechanism is complementary to
   existing PW protection mechanisms.

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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   This Internet-Draft will expire on October 28, 2017.

Copyright Notice

   Copyright (c) 2017 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
   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
   2.  Reference Models of Dual-homing Local Protection  . . . . . .   3
     2.1.  PE Architecture . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Dual-Homing Local Protection Reference Scenarios  . . . .   4
       2.2.1.  One-Side Dual-Homing Protection . . . . . . . . . . .   4
       2.2.2.  Two-side Dual-Homing Protection . . . . . . . . . . .   6
   3.  Generic Dual-homing PW Protection Mechanism . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   [RFC6372] and [RFC6378] describe the framework and mechanism of MPLS-
   TP Linear protection, which can provide protection for the MPLS LSP
   or pseudowire (PW) between the edge nodes.  This mechanism does not
   protect the failure of the Attachment Circuit (AC) or the Provider
   Edge (PE) node.  [RFC6718] and [RFC6870] describe the framework and
   mechanism for PW redundancy to provide protection for AC or PE node
   failure.  The PW redundancy mechanism is based on the signaling of
   Label Distribution Protocol (LDP), which is applicable to PWs with a
   dynamic control plane.  [I-D.ietf-pals-endpoint-fast-protection]
   describes a fast local repair mechanism for PW egress endpoint
   failures, which is based on PW redundancy, upstream label assignment
   and context specific label switching.  The mechanism defined in
   [I-D.ietf-pals-endpoint-fast-protection] is only applicable to PWs
   with a dynamic control plane.

   There is a need to support a dual-homing local protection mechanism
   which avoids unnecessary switches of the AC or PW, and which can be
   used regardless if a control plane is used.  In some scenarios such
   as mobile backhauling, the MPLS PWs are provisioned with dual-homing



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   topology, in which at least the CE node on one side is dual-homed to
   two PEs.  If some fault occurs in the primary AC, operators usually
   prefer to have the switchover only on the dual-homing PE side and
   keep the working pseudowires unchanged if possible.  This is to avoid
   massive PW switchover in the mobile backhaul network due to the AC
   failure in the mobile core site, which may in turn lead to congestion
   due to the migration of traffic from the paths preferred by the
   network planners.  Similarly, as multiple PWs share the physical AC
   in the mobile core site, it is preferable to keep using the working
   AC when one working PW fails in PSN network, which could avoid
   unnecessary switchover for other PWs.  To meet the above
   requirements, a fast dual-homing local PW protection mechanism is
   needed to protect against the failures of an AC, the PE node, and the
   PSN network.

   This document describes the framework and several typical scenarios
   of pseudowire (PW) dual-homing local protection.  A Dual-Node
   Interconnection (DNI) PW is used between the dual-homing PE nodes for
   carrying traffic when a failure occurs in the AC or PW side.  In
   order for the dual-homing PE nodes to determine the forwarding state
   of AC, PW and DNI PW, necessary state exchange and coordination
   between the dual-homing PEs is needed.  The necessary mechanisms and
   protocol extensions are defined in a companion document
   [I-D.ietf-pals-mpls-tp-dual-homing-coordination].

2.  Reference Models of Dual-homing Local Protection

   This section shows the reference architecture of the dual-homing PW
   local protection and the usage of the architecture in different
   scenarios.

2.1.  PE Architecture

   Figure 1 shows the PE architecture for dual-homing local protection.
   This is based on the architecture in Figure 4a of [RFC3985].  In
   addition to the AC and the service PW between the local and remote
   PEs, a DNI PW is used to connect the forwarders of the dual-homing
   PEs.  It can be used to forward traffic between the dual-homing PEs
   when a failure occurs in the AC or service PW side.  As [RFC3985]
   specifies: "any required switching functionality is the
   responsibility of a forwarder function", in this case, the forwarder
   is responsible for switching the payloads between three entities: the
   AC, the service PW and the DNI PW.








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            +----------------------------------------+
            |          Dual-homing PE Device         |
            +----------------------------------------+
       AC   |                 |                      | Service PW
    <------>o    Forwarder    +       Service        X<===========>
            |                 |         PW           |
            +--------+--------+                      |
            |     DNI PW      |                      |
            +--------X--------+----------------------+
                     ^
                     |  DNI PW
                     |
                     V
            +--------X--------+----------------------+
            |     DNI PW      |                      |
            +--------+--------+                      | Service PW
       AC   |                 |       Service        X<===========>
    <------>o    Forwarder    +         PW           |
            |                 |                      |
            +----------------------------------------+
            |          Dual-homing PE Device         |
            +----------------------------------------+
       Figure 1: PE Architecture for Dual-homing Protection

2.2.  Dual-Homing Local Protection Reference Scenarios

2.2.1.  One-Side Dual-Homing Protection

   Figure 2 illustrates the network scenario of dual-homing PW local
   protection where only one of the CEs is dual-homed to two PE nodes.
   CE1 is dual-homed to PE1 and PE2, while CE2 is single-homed to PE3.
   A DNI-PW is established between the dual-homing PEs, which is used to
   bridge traffic when a failure occurs in the PSN network or in the AC
   side.  A dual-homing control mechanism enables the PEs and CE to
   determine which AC should be used to carry traffic between CE1 and
   the PSN network.  The necessary control mechanisms and protocol
   extensions are defined in a companion document
   [I-D.ietf-pals-mpls-tp-dual-homing-coordination].

   This scenario can protect the node failure of PE1 or PE2, or the
   failure of one of the ACs between CE1 and the dual-homing PEs.  In
   addition, dual-homing PW protection can protect a failure occuring in
   the PSN network which impacts the working PW, thus it can be an
   alternative solution of PSN tunnel protection mechanisms.  This
   topology can be used in mobile backhauling application scenarios.
   For example, CE2 might be a cell site equipment such as a NodeB,
   whilst CE1 is the shared Radio Network Controller (RNC).  PE3




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   functions as an access side MPLS device while PE1 and PE2 function as
   core side MPLS devices.

           |<--------------- Emulated Service --------------->|
           |                                                  |
           |          |<------- Pseudo Wire ------>|          |
           |          |                            |          |
           |          |    |<-- PSN Tunnels-->|    |          |
           |          V    V                  V    V          |
           V    AC1   +----+                  +----+          V
     +-----+    |     | PE1|                  |    |          +-----+
     |     |----------|........PW1.(working).......|          |     |
     |     |          |    |                  |    |          |     |
     |     |          +-+--+                  |    |     AC3  |     |
     |     |            |                     |    |     |    |     |
     | CE1 |     DNI-PW |                     |PE3 |----------| CE2 |
     |     |            |                     |    |          |     |
     |     |          +-+--+                  |    |          |     |
     |     |          |    |                  |    |          |     |
     |     |----------|......PW2.(protection)......|          |     |
     +-----+    |     | PE2|                  |    |          +-----+
                AC2   +----+                  +----+
               Figure 2. One-side dual-homing PW protection

   Consider in normal state AC1 from CE1 to PE1 is initially active and
   AC2 from CE1 to PE2 is initially standby, PW1 is the working PW and
   PW2 is the protection PW.

   When a failure occurs in AC1, then the state of AC2 changes to active
   based on the AC dual-homing control mechanism.  In order to keep the
   switchover local and continue using PW1 for traffic forwarding as
   preferred according to traffic planning, the forwarder on PE2 needs
   to connect AC2 to the DNI PW, and the forwarder on PE1 needs to
   connect the DNI PW to PW1.  In this way the failure in AC1 will not
   impact the forwarding of the service PWs across the network.  After
   the switchover, traffic will go through the bidirectional path: CE1-
   (AC2)-PE2-(DNI-PW)-PE1-(PW1)-PE3-(AC3)-CE2.

   When a failure in the PSN network affects the working PW (PW1),
   according to PW protection mechanisms [RFC6378], traffic is switched
   onto the protection PW (PW2), while the state of AC1 remains active.
   Then the forwarder on PE1 needs to connect AC1 to the DNI PW, and the
   forwarder on PE2 needs to connect the DNI PW to PW2.  In this way the
   failure in the PSN network will not impact the state of the ACs.
   After the switchover, traffic will go through the bidirectional path:
   CE1-(AC1)-PE1-(DNI-PW)-PE2-(PW2)-PE3-(AC3)-CE2.





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   When a failure occurs in the working PE (PE1), it is equivalent to a
   failure of the working AC, the working PW and the DNI PW.  The state
   of AC2 changes to active based on the AC dual-homing control
   mechanism.  And according to the PW protection mechanism, traffic is
   switched on to the protection PW "PW2".  In this case the forwarder
   on PE2 needs to connect AC2 to PW2.  After the switchover, traffic
   will go through the bidirectional path: CE1-(AC2)-PE2-(PW2)-PE3-
   (AC3)-CE2.

2.2.2.  Two-side Dual-Homing Protection

   Figure 3 illustrates the network scenario of dual-homing PW
   protection where the CEs in both sides are dual-homed.  CE1 is dual-
   homed to PE1 and PE2, and CE2 is dual-homed to PE3 and PE4.  A dual-
   homing control mechanism enables the PEs and CEs to determine which
   AC should be used to carry traffic between CE and the PSN network.
   DNI-PWs are used between the dual-homing PEs on both sides.  One
   service PW is established between PE1 and PE3, another service PW is
   established between PE2 and PE4.  The role of working and protection
   PW can be determined either by configuration or via existing
   signaling mechanisms.

   This scenario can protect the node failure on one of the dual-homing
   PEs, or the failure on one of the ACs between the CEs and their dual-
   homing PEs.  Also, dual-homing PW protection can protect if the
   failure occured in the PSN network which impacts one of the PWs, thus
   it can be used as an alternative solution of PSN tunnel protection
   mechanisms.  Note, this scenario is mainly used for services
   requiring high availability as it requires redundancy of the PEs and
   network utilization.  In this case, CE1 and CE2 can be regarded as
   service access points.




















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           |<---------------- Emulated Service -------------->|
           |                                                  |
           |          |<-------- Pseudowire ------>|          |
           |          |                            |          |
           |          |    |<-- PSN Tunnels-->|    |          |
           |          V    V                  V    V          |
           V    AC1   +----+                  +----+     AC3  V
     +-----+    |     | ...|...PW1.(working)..|... |     |    +-----+
     |     |----------| PE1|                  | PE3|----------|     |
     |     |          +----+                  +----+          |     |
     |     |            |                        |            |     |
     | CE1 |    DNI-PW1 |                        |  DNI-PW2   | CE2 |
     |     |            |                        |            |     |
     |     |          +----+                  +----+          |     |
     |     |          |    |                  |    |          |     |
     |     |----------| PE2|                  | PE4|--------- |     |
     +-----+    |     | ...|.PW2.(protection).|... |     |    +-----+
                AC2   +----+                  +----+     AC4

                Figure 3. Two-side dual-homing PW protection

   Consider in normal state, AC1 between CE1 and PE1 is initially active
   and AC2 between CE1 and PE2 is initially standby, AC3 between CE2 and
   PE3 is initially active and AC4 from CE2 to PE4 is initially standby,
   PW1 is the working PW and PW2 is the protection PW.

   When a failure occurs in AC1, the state of AC2 changes to active
   based on the AC dual-homing control mechanism.  In order to keep the
   switchover local and continue using PW1 for traffic forwarding, the
   forwarder on PE2 needs to connect AC2 to the DNI-PW1, and the
   forwarder on PE1 needs to connect DNI-PW1 with PW1.  In this way
   failures in the AC side will not impact the forwarding of the service
   PWs across the network.  After the switchover, traffic will go
   through the bidirectional path: CE1-(AC2)-PE2-(DNI-PW1)-PE1-(PW1)-
   PE3-(AC3)-CE2.

   When a failure occurs in the working PW (PW1), according to the PW
   protection mechanism [RFC6378], traffic needs to be switched onto the
   protection PW "PW2".  In order to keep the state of AC1 and AC3
   unchanged, the forwarder on PE1 needs to connect AC1 to DNI-PW1, and
   the forwarder on PE2 needs to connect DNI-PW1 to PW2.  On the other
   side, the forwarder of PE3 needs to connect AC3 to DNI-PW2, and the
   forwarder on PE4 needs to connect PW2 to DNI-PW2.  In this way, the
   state of the ACs will not be impacted by the failure in the PSN
   network.  After the switchover, traffic will go through the
   bidirectional path: CE1-(AC1)-PE1-(DNI-PW1)-PE2-(PW2)-PE4-(DNI-PW2)-
   PE3-(AC3)-CE2.




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   When a failure occurs in the working PE (PE1), it is equivalent to
   the failures of the working AC, the working PW and the DNI PW.  The
   state of AC2 changes to active based on the AC dual-homing control
   mechanism.  And according to the PW protection mechanism, traffic is
   switched on to the protection PW "PW2".  In this case the forwarder
   on PE2 needs to connect AC2 to PW2, and the forwarder on PE4 needs to
   connect PW2 to DNI-PW2.  After the switchover, traffic will go
   through the bidirectional path: CE1-(AC2)-PE2-(PW2)-PE4-(DNI-PW2)-
   PE3-(AC3)-CE2.

3.  Generic Dual-homing PW Protection Mechanism

   As shown in the above scenarios, with the described dual-homing PW
   protection, failures in the AC side will not impact the forwarding
   behavior of the PWs in the PSN network, and vice-versa.

   In order for the dual-homing PEs to coordinate the traffic forwarding
   during the failures, synchronization of the status information of the
   involved entities and coordination of switchover between the dual-
   homing PEs are needed.  For PWs with a dynamic control plane, such
   information synchronization and coordination can be achieved with a
   dynamic protocol, such as [RFC7275], possibly with some extensions.
   For PWs which are manually configured without a control plane, a new
   mechanism is needed to exchange the status information and coordinate
   switchover between the dual-homing PEs, e.g. over an embedded PW
   control channel.  This is described in a companion document
   [I-D.ietf-pals-mpls-tp-dual-homing-coordination].

4.  IANA Considerations

   This document does not require any IANA action.

5.  Security Considerations

   The scenarios defined in this document do not affect the security
   model as defined in [RFC3985].

   With the proposed protection mechanism, the disruption of a dual-
   homed AC, a component which is outside the core network, would have a
   reduced impact on the traffic flows in the core network.  This could
   also avoid unnecessary congestion in the core network.

   The security consideration of the DNI PW is the same as for Service
   PWs in the data plane [RFC3985].  Security considerations for the
   coordination/control mechanism will be addressed in the companion
   document that defines the mechanism.





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6.  Contributors

   The following individuals substantially contributed to the content of
   this document:

   Kai Liu
   Huawei Technologies
   Email: alex.liukai@huawei.com

   Alessandro D'Alessandro
   Telecom Italia
   alessandro.dalessandro@telecomitalia.it

7.  References

7.1.  Normative References

   [I-D.ietf-pals-mpls-tp-dual-homing-coordination]
              Cheng, W., Wang, L., Li, H., Dong, J., and A.
              D'Alessandro, "Dual-Homing Coordination for MPLS Transport
              Profile (MPLS-TP) Pseudowires Protection", draft-ietf-
              pals-mpls-tp-dual-homing-coordination-05 (work in
              progress), January 2017.

   [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>.

7.2.  Informative References

   [I-D.ietf-pals-endpoint-fast-protection]
              Shen, Y., Aggarwal, R., Henderickx, W., and Y. Jiang, "PW
              Endpoint Fast Failure Protection", draft-ietf-pals-
              endpoint-fast-protection-05 (work in progress), January
              2017.

   [RFC6372]  Sprecher, N., Ed. and A. Farrel, Ed., "MPLS Transport
              Profile (MPLS-TP) Survivability Framework", RFC 6372,
              DOI 10.17487/RFC6372, September 2011,
              <http://www.rfc-editor.org/info/rfc6372>.

   [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>.





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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>.

   [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>.

   [RFC7275]  Martini, L., Salam, S., Sajassi, A., Bocci, M.,
              Matsushima, S., and T. Nadeau, "Inter-Chassis
              Communication Protocol for Layer 2 Virtual Private Network
              (L2VPN) Provider Edge (PE) Redundancy", RFC 7275,
              DOI 10.17487/RFC7275, June 2014,
              <http://www.rfc-editor.org/info/rfc7275>.

Authors' Addresses

   Weiqiang Cheng
   China Mobile
   No.32 Xuanwumen West Street
   Beijing  100053
   China

   Email: chengweiqiang@chinamobile.com


   Lei Wang
   China Mobile
   No.32 Xuanwumen West Street
   Beijing  100053
   China

   Email: Wangleiyj@chinamobile.com


   Han Li
   China Mobile
   No.32 Xuanwumen West Street
   Beijing  100053
   China

   Email: Lihan@chinamobile.com








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   Shahram Davari
   Broadcom Corporation
   3151 Zanker Road
   San Jose  95134-1933
   United States

   Email: davari@broadcom.com


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

   Email: jie.dong@huawei.com



































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