Network Working Group                                           W. Cheng
Internet-Draft                                                   L. Wang
Intended status: Informational                                     H. Li
Expires: September 22, 2016                                  China Mobile
                                                                  K. Liu
                                                     Huawei Technologies
                                                               S. Davari
                                                    Broadcom Corporation
                                                                 J. Dong
                                                     Huawei Technologies
                                                         A. D'Alessandro
                                                          Telecom Italia
                                                           March 21, 2016


        Dual-Homing Protection for MPLS and MPLS-TP Pseudowires
           draft-ietf-pals-mpls-tp-dual-homing-protection-02

Abstract

   This document describes a framework and several scenarios for
   pseudowire (PW) dual-homing local protection.  A Dual-Node
   Interconnection (DNI) PW is provisioned between the dual-homing
   Provider Edge (PE) nodes for carrying traffic when failure occurs in
   the Attachment Circuit (AC) or PW side.  In order for the dual-homing
   PE nodes to determine the forwarding state of AC, PW and the DNI PW,
   necessary state exchange and coordination between the dual-homing PEs
   are needed.  The PW dual-homing local protection mechanism is
   complementary to the existing PW protection mechanisms.

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
   and may be updated, replaced, or obsoleted by other documents at any



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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 September 22, 2016.

Copyright Notice

   Copyright (c) 2016 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
   to this document.  Code Components extracted from this document must
   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 . . . . . . . . .   7
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

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.  Such 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



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   failures, which is based on PW redundancy, upstream label assignment
   and context specific label switching.  Such mechanism is applicable
   to PWs with a dynamic control plane.

   In some scenarios such as mobile backhauling, the MPLS PWs are
   provisioned with dual-homing topology, in which at least the CE node
   in one side is dual-homed to two PEs.  If some fault occurs in the
   primary AC, operators usually prefer to have the switchover only in
   the dual-homing PE side and keeps the working pseudowires unchanged
   if possible.  This is to avoid massive PWs switchover in the mobile
   backhaul network due to one AC failure in the core site, and also
   could achieve efficient and balanced link bandwidth utilization.
   Similarly, it is preferable to keep using the working AC when one
   working PW fails in the Packet Switched Network (PSN) network.  To
   meet the above requirement, a fast dual-homing PW local protection
   mechanism is needed to protect the failures in AC, the PE node and
   the PSN network.

   This document describes the framework and typical scenarios for
   pseudowire (PW) dual-homing local protection.  A Dual-Node
   Interconnection (DNI) PW is provisioned between the dual-homing PE
   nodes for carrying traffic when 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 mechanism defined in this
   document is complementary to the existing protection mechanisms.  The
   necessary protocol extensions will be described in a separate
   document.

   The proposed mechanism has been deployed in several mobile backhaul
   networks which use static MPLS-TP PWs for the backhauling of mobile
   traffic.

2.  Reference Models of Dual-homing Local Protection

   This section shows the reference architecture of the PE for 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, a DNI PW is provisioned to
   connect the forwarders of the dual-homing PEs.  It can be used to
   forward traffic between the dual-homing PEs when failure occurs in
   the AC or service PW side.  As [RFC3985] specifies: "any required
   switching functionality is the responsibility of a forwarder



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   function", in this case, the forwarder is responsible for switching
   the payloads between three entities: the AC, the service PW and the
   DNI PW.  The specific behavior of forwarder is determined according
   to the forwarding state machine defined in this document.

            +----------------------------------------+
            |          Dual-homing PE Device         |
     Single +----------------------------------------+
       AC   |                 |                      | Service PW
    <------>o    Forwarder    +       Service        X<===========>
            |                 |         PW           |
            +--------+--------+                      |
            |     DNI PW      |                      |
            +--------X--------+----------------------+
                     ^
                     |  DNI PW
                     |
                     V
            +--------X-------------------------------+
            |       Peer 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 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.  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 control mechanism enables the PEs and CE to determine which
   AC should be used to carry traffic between CE1 and the PSN network.
   These mechanisms/protocols are beyond the scope of this document.
   The working and protection PWs can be determined either by
   configuration or by existing signaling mechanisms.

   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 the failure occured
   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, the NodeB serves as CE2 while the Radio Network
   Controller (RNC) serves as CE1.  PE3 works as an access side MPLS
   device while PE1 and PE2 works as core side MPLS devices.



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           |<--------------- 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 some AC redundancy 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 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 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, 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 path: CE1-(AC1)-
   PE1-(DNI-PW)-PE2-(PW2)-PE3-(AC3)-CE2.

   In both AC and PW failure cases, the dual-homing PW protection needs
   to coordinate the PEs to set the forwarding state between the AC,
   service PW and DNI PW properly.





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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 provisioned 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.  Meanwhile, dual-homing PW protection can protect the
   failure occured in the PSN network which impacts one of the PWs, thus
   it can be an alternative solution of PSN tunnel protection
   mechanisms.  This scenario is mainly used for services of important
   business customers.  In this case, CE1 and CE2 can be regarded as
   service access points.

           |<---------------- 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 from CE1 to PE1 is initially active and
   AC2 from CE1 to PE2 is initially standby, AC3 from CE2 to PE3 is
   initially active and AC4 from CE2 to PE4 is initially standby, PW1 is
   the working PW and PW2 is the protection PW.




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   When a failure occurs in AC1, the state of AC2 changes to active
   based on some AC redundancy 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 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, traffic is 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 path: CE1-(AC1)-
   PE1-(DNI-PW1)-PE2-(PW2)-PE4-(DNI-PW2)-PE3-(AC3)-CE2.

   In case both the AC and PW failure occur, the dual-homing PW
   protection needs to coordinate the PEs to set the forwarding state
   between the AC, service PW and the DNI PW properly.

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.  This is
   achieved by properly setting the forwarding state between the
   following entities:

   o  AC

   o  Service PW

   o  DNI PW

   The forwarding behavior of the dual-homing PE nodes are determined by
   the forwarding state machine as shown in table 1:











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          +-----------+---------+--------+---------------------+
          |Service PW |   AC    | DNI PW | Forwarding Behavior |
          +-----------+---------+--------+---------------------+
          |  Active   | Active  |   Up   |Service PW <-> AC    |
          +-----------+---------+--------+---------------------+
          |  Active   | Standby |   Up   |Service PW <-> DNI PW|
          +-----------+---------+--------+---------------------+
          |  Standby  | Active  |   Up   |    DNI PW <-> AC    |
          +-----------+---------+--------+---------------------+
          |  Standby  | Standby |   Up   |  Drop all packets   |
          +-----------+---------+--------+---------------------+
             Table 1. Dual-homing PE Forwarding State Machine

   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.  This is described in a
   separate document.

4.  IANA Considerations

   This document does not require any IANA action.

5.  Security Considerations

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

6.  References

6.1.  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>.

   [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>.





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6.2.  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-02 (work in progress), January
              2016.

   [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>.

   [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








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   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


   Kai Liu
   Huawei Technologies
   Huawei Base, Bantian, Longgang District
   Shenzhen  518129
   China

   Email: alex.liukai@huawei.com


   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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   Alessandro D'Alessandro
   Telecom Italia
   via Reiss Romoli, 274
   Torino  10148
   Italy

   Email: alessandro.dalessandro@telecomitalia.it












































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