Network Working Group                                           W. Cheng
Internet-Draft                                                   L. Wang
Intended status: Standards Track                                   H. Li
Expires: February 2, 2017                                   China Mobile
                                                                  K. Liu
                                                     Huawei Technologies
                                                               S. Davari
                                                    Broadcom Corporation
                                                                 J. Dong
                                                     Huawei Technologies
                                                         A. D'Alessandro
                                                          Telecom Italia
                                                          August 1, 2016


     Dual-Homing Coordination for MPLS Transport Profile (MPLS-TP)
                         Pseudowires Protection
          draft-ietf-pals-mpls-tp-dual-homing-coordination-04

Abstract

   In some scenarios, the MPLS Transport Profile (MPLS-TP) Pseudowires
   (PWs) are provisioned through either static configuration or
   management plane, where a dynamic control plane is not available.  A
   fast protection mechanism for MPLS-TP PWs is needed to protect
   against the failure of Attachment Circuit (AC), the failure of
   Provider Edge (PE) and also the failure in the Packet Switched
   Network (PSN).  The framework and typical scenarios of dual-homing PW
   local protection are described in [draft-ietf-pals-mpls-tp-dual-
   homing-protection].  This document proposes a dual-homing
   coordination mechanism for MPLS-TP PWs, which is used for state
   exchange and switchover coordination between the dual-homing PEs for
   dual-homing PW local protection.

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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   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
   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 February 2, 2017.

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.  Overview of the Proposed Solution . . . . . . . . . . . . . .   3
   3.  Protocol Extensions for Dual-Homing MPLS-TP PW Protection . .   4
     3.1.  Information Exchange Between Dual-Homing PEs  . . . . . .   4
     3.2.  Protection Procedures . . . . . . . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   [RFC6372], [RFC6378] and [RFC7771] describe the framework and
   mechanism of MPLS-TP Linear protection, which can provide protection
   for the MPLS LSP and PW between the edge nodes.  These mechanisms
   cannot protect the failure of the Attachment Circuit (AC) or the edge
   nodes.  [RFC6718] and [RFC6870] specifies the PW redundancy framework
   and mechanism for protecting the AC or edge node failure by adding
   one or more edge nodes, but it requires PW switchover in case of a AC



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   failure, also PW redundancy relies on PSN protection mechanisms to
   protect the failure of PW.

   In some scenarios such as mobile backhauling, the MPLS PWs are
   provisioned with dual-homing topology, in which at least the CE node
   on one side is dual-homed to two PEs.  If a failure occurs in the
   primary AC, operators usually prefer to perform local switchover in
   the dual-homing PE side and keep the working pseudowire 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 muliple
   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 the PSN
   network, which could avoid unnecessary AC switchover for other PWs.
   A fast dual-homing PW protection mechanism is needed to protect the
   failure in AC, the PE node and the PSN network to meet the above
   requirements.

   [I-D.ietf-pals-mpls-tp-dual-homing-protection] describes a framework
   and several scenarios of dual-homing pseudowire (PW) local
   protection.  This document proposes a dual-homing coordination
   mechanism for static MPLS-TP PWs, which is used for information
   exchange and switchover coordination between the dual-homing PEs for
   the dual-homing PW local protection.  The proposed mechanism has been
   implemented and deployed in several mobile backhaul networks which
   use static MPLS-TP PWs for the backhauling of mobile traffic from the
   radio access sites to the core site.

2.  Overview of the Proposed Solution

   Linear protection mechanisms for MPLS-TP network are defined in
   [RFC6378], [RFC7271] and [RFC7324].  When such mechanisms are applied
   to PW linear protection [RFC7771], both the working PW and the
   protection PW are terminated on the same PE node.  In order to
   provide dual-homing protection for MPLS-TP PWs, some additional
   mechanisms are needed.

   In MPLS-TP PW dual-homing protection, the linear protection mechanism
   as defined in [RFC6378] [RFC7271] and [RFC7324] on the single-homing
   PE (e.g.  PE3 in figure 1) is not changed, while on the dual-homing
   side, the working PW and protection PW are terminated on two dual-
   homing PEs (e.g.  PE1 and PE2 in figure 1) respectively to protect
   the failure occurs in the dual-homing PEs and the connected ACs.  As
   specified in [I-D.ietf-pals-mpls-tp-dual-homing-protection], a
   dedicated Dual-Node Interconnection (DNI) PW is provisioned between
   the two dual-homing PE nodes, which is used to bridge the traffic
   between the dual-homing PEs when a failure happens in the working PW



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   or the primary AC.  In order to make the linear protection mechanism
   work in the dual-homing PEs scenario, coordination between the dual-
   homing PE nodes is needed, so that the dual-homing PEs can set the
   connection between the AC, the service PW and the DNI-PW properly in
   a coordinated fashion.

               +----------------+
               /                |                +--------+
          AC1 /|   PE1          |  Working PW    |        |
             / |                X----------------X        |
            /  |                |  Service PW1   |        |
       +---/+  +--------X-------+                |        |   +----+
       |    |           | DNI PW                 |  PE3   |   |    |
       | CE1|           |                        |        |---| CE2|
       +---\+  +--------X-------+                |        |   +----+
            \  |                | Protection PW  |        |
             \ |                X----------------X        |
          AC2 \|                |  Service PW2   |        |
               \   PE2          |                +--------+
               +----------------+

              Figure 1. Dual-homing Protection with DNI-PW

3.  Protocol Extensions for Dual-Homing MPLS-TP PW Protection

   In dual-homing MPLS-TP PW local protection, the forwarding state of
   the dual-homing PEs are determined by the forwarding state machine as
   defined in [I-D.ietf-pals-mpls-tp-dual-homing-protection].  In order
   to achieve the dual-homing MPLS-TP PW protection, coordination
   between the dual-homing PE nodes is needed to exchange the PW status
   and protection coordination requests.

3.1.  Information Exchange Between Dual-Homing PEs

   The coordination information will be sent on the DNI PW over the
   G-ACh as described in [RFC5586].  A new G-ACh channel type is defined
   for the dual-homing coordination between the dual-homing PEs of MPLS-
   TP PWs.  This channel type can be used for the exchange of different
   kinds of information between the dual-homing PEs.  This document uses
   this channel type for the exchange of PW status and switchover
   coordination between the dual-homing PEs.  Other potential usages of
   this channel type are for further study and are out of the scope of
   this document.

   The MPLS-TP Dual-Homing Coordination (DHC) message is sent on the DNI
   PW between the dual-homing PEs.  The format of MPLS-TP DHC message is
   shown below:




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   0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0 0 0 1|Version|     Flags     |         DHC Code Point        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Dual-Homing PEs Group ID                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         TLV  Length           |           Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                              TLVs                             ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          Figure 2. MPLS-TP Dual-Homing Coordination Message

   The Dual-Homing Group ID is a 4-octet unsigned integer to identify
   the dual-homing group which the dual-homing PEs belong to.  It MUST
   be the same at both PEs in the same group.

   The TLV Length field specifies the total length in octets of the
   subsequent TLVs.

   In this document, two TLVs are defined in MPLS-TP Dual-Homing
   Coordination message for dual-homing MPLS-TP PW protection:

   Type        Description                Length
    1           PW Status                 20 Bytes
    2        Dual-Node Switching         16 Bytes

   The PW Status TLV is used by a dual-homing PE to report its service
   PW status to the other dual-homing PE in the same dual-homing group.

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Type=1 (PW Status)         |          Length               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              Destination Dual-homing PE Node_ID               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Source Dual-homing PE Node_ID                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         DNI PW-ID                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Flags                               |P|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Service PW Status                     |D|F|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      Figure 3. PW Status TLV





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   - The Length field specifies the length in octets of the value field
   of the TLV.

   - The Destination Dual-homing PE Node_ID is the 32-bit identifier of
   the receiver PE.  Usually it is the same as the LSR-ID of the
   receiver PE.

   - The Source Dual-homing PE Node_ID is the 32-bit identifier of the
   sending PE.  Usually it is the same as the LSR-ID of the sending PE.

   - The DNI PW-ID field contains the 32-bit PW ID of the DNI PW.

   - The Flags field contains 32 bit flags, in which:

   o  The P (Protection) bit indicates whether the Source Dual-homing PE
      is the working PE (P=0) or the protection PE (P=1).

   o  Other bits are reserved for future use, which MUST be set to 0 on
      transmission and MUST be ignored upon receipt.

   - The Service PW Status field indicates the status of the Service PW
   between the sending PE and the remote PE.  Currently two bits are
   defined in the Service PW Status field:

   o  F bit: If set, it indicates Signal Fail (SF) [RFC6378] is
      generated on the service PW.  It can be either a local request or
      a remote request received from the remote PE.

   o  D bit: If set, it indicates Signal Degrade (SD) [RFC6378]
      generated on the service PW.  It can be either a local request or
      a remote request received from the remote PE.

   o  Other bits are reserved for future use, which MUST be set to 0 on
      transmission and MUST be ignored upon receipt.

   The Dual-Node Switching TLV is used by one dual-homing PE to send
   protection state coordination to the other PE in the same dual-homing
   group.













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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Type=2 (Dual-Node Switching) |          Length               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Destination Dual-homing PE Node_ID               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                Source Dual-homing PE Node_ID                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         DNI PW-ID                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Flags                            |S|P|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      Figure 4. Dual-Node Switching TLV

   - The Length field specifies the length in octets of the value field
   of the TLV.

   - The Destination Dual-homing PE Node_ID is the 32-bit identifier of
   the receiver PE.  Usually it is the same as the LSR-ID of the
   receiver PE.

   - The Source Dual-homing PE Node_ID is the 32-bit identifier of the
   sending PE.  Usually it is the same as the LSR-ID of the sending PE.

   - The DNI PW-ID field contains the 32-bit PW-ID of the DNI PW.

   - The Flags field contains 32 bit flags, in which:

   o  The P (Protection) bit indicates whether the Source Dual-homing PE
      is the working PE or the protection PE.  It is set to 1 when the
      Source PE of the dual-node switching request is the protection PE.

   o  The S (PW Switching) bit indicates which service PW is used for
      forwarding traffic.  It is set to 0 when traffic will be
      transported on the working PW, and is set to 1 if traffic will be
      transported on the protection PW.  The value of the S bit is
      determined by the protection coordination mechanism between the
      dual-homing PEs and the remote PE.

   o  Other bits are reserved for future use, which MUST be set to 0 on
      transmission and MUST be ignored upon receipt.

   When a change of the service PW status is detected by one of the
   dual-homing PEs, it MUST be reflected in the PW Status TLV and sent
   to the other dual-homing PE immediately using 3 consecutive rapid DHC
   messages.  After the transmission of the three rapid messages, the
   dual-homing PE MUST send the most recently transmitted service PW



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   status periodically to the other dual-homing PE using the continual
   DHC message.

   When one dual-homing PE determines that the active service PW needs
   to be switched from the working PW to the protection PW, It MUST send
   the Dual-Node Switching TLV to the other dual-homing PE immediately
   using 3 consecutive rapid DHC messages.  After the transmission of
   the three rapid messages, the dual-homing PE MUST send the most
   recently transmitted Dual-Node Switching TLV periodically to the
   other dual-homing PE using the continual DHC messages.

   It is RECOMMENDED that the default interval of the first three rapid
   DHC messages is 3.3 ms, and the default interval of the subsequent
   messages is 1 second.  Both the default frequency of the three rapid
   messages as well as the default frequency of the continual message
   transmission SHALL be configurable by the operator.

3.2.  Protection Procedures

   The dual-homing MPLS-TP PW protection mechanism can be deployed with
   the existing AC redundancy mechanisms.  On the PSN network side, PSN
   tunnel protection mechanism is not required, as the dual-homing PW
   protection can also protect the failure occurred in the PSN network.

   This section takes one-side dual-homing scenario as an example to
   describe the dual-homing PW protection procedures, the procedures for
   two-side dual-homing scenario would be similar.

   On dual-homing PE side, the role of working and protection PE are set
   by NMS or local configuration.  The service PW connecting to the
   working PE is the working PW, and the service PW connecting to the
   protection PE is called the protection PW.

   On single-homing PE side, it just treats the working PW and
   protection PW as if they terminate on the same remote PE node, thus
   normal MPLS-TP protection coordination procedures still apply on the
   single-homing PE.

   The forwarding behavior of the dual-homing PEs is determined by the
   components shown in the figure below:











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             +---------------------------------+          +-----+
             |        PE1 (Working PE)         |          |     |
             +---------------------------------+          |     |
             |                 |               |    PW1   |     |
             +    Forwarder    +    Service    X<-------->X     |
            /|                 |      PW       |  Working |     |
           / +--------+--------+               |    PW    |     |
     AC1  /  |     DNI PW      |               |          |     |
         /   +--------X--------+---------------+          |     |
 +-----+/             ^                                   |     |
 | CE1 |              |  DNI PW                           | PE3 |  +---+
 +-----+              |                                   |     ---|CE3|
        \             V                                   |     |  +---+
     AC2 \   +--------X--------+---------------+          |     |
          \  |     DNI PW      |               |          |     |
           \ +--------+--------+               |          |     |
            \|                 |     Service   |    PW2   |     |
             +    Forwarder    +       PW      X<-------->X     |
             |                 |               |Protection|     |
             +---------------------------------+     PW   |     |
             |        PE2 (Protection PE)      |          |     |
             +---------------------------------+          +-----+
          Figure 5. Components of one-side dual-homing PW protection

   In figure 5, for each dual-homing PE, service PW is the PW used to
   carry service between the dual-homing PE and the remote PE.  The
   state of the service PW is determined by the OAM mechanisms between
   the dual-homing PEs and the remote PE.

   DNI PW is provisioned between the two dual-homing PE nodes.  It is
   used to bridge traffic when failure occurs in the PSN network or in
   the ACs.  The state of DNI PW is determined by the OAM mechanism
   between the dual-homing PEs.  Since DNI PW is used to carry both the
   coordination messages and the service traffic during protection
   switching, it is important to ensure the robustness of the DNI PW.
   In order to avoid the DNI PW failure due to the failure of a
   particular link, it is RECOMMENDED that multiple diverse links be
   deployed between the dual-homing PEs and the underlay LSP protection
   mechanism SHOULD be enabled.

   AC is the link which connects a dual-homing PE to the dual-homed CE.
   The status of AC is determined by some existing AC redundancy
   mechanisms, which is out of the scope of this document.

   In order to perform dual-homing PW local protection, the service PW
   status and Dual-node switching coordination requests are exchanged
   between the dual-homing PEs using the DHC message defined above.




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   Whenever a change of service PW status is detected by a dual-homing
   PE, it MUST be reflected in the PW Status TLV and sent to the other
   dual-homing PE immediately using using 3 consecutive rapid DHC
   messages.  This way, both dual-homing PEs have the status of the
   working and protection PW consistently.

   When there is a switchover request either generated locally or
   received on the protection PW from the remote PE, based on the status
   of the working and protection service PW, along with the local and
   remote request of the protection coordination between the dual-homing
   PEs and the remote PE, the active/standby state of the service PW can
   be determined by the dual-homing PEs.  As the remote protection
   coordination request is transmitted over the protection path, in this
   case the active/standby status of the service PW is determined by the
   protection PE in the dual-homing group.

   If it is determined on one dual-homing PE that switchover of service
   PW is needed, this dual-homing PE MUST set the S bit in the Dual-Node
   Switching TLV and send it to the other dual-homing PE immediately
   using 3 consecutive rapid DHC messages.  With the exchange of service
   PW status and the switching request, both dual-homing PEs are
   consistent on the Active/Standby forwarding status of the working and
   protection service PWs.  The status of DNI PW is determined by OAM
   mechanism, and the status of ACs are determined by existing AC
   redundancy mechanism, which is out of the scope of this document.
   The forwarding behavior on the dual-homing PE nodes is determined by
   the forwarding state machine as shown in table 1 of
   [I-D.ietf-pals-mpls-tp-dual-homing-protection].

   Take the topology in figure 5 as an example, in normal state, the
   working PW (PW1) is in active state, the protection PW (PW2) is in
   standby state, the DNI PW is up, and AC1 is in active state according
   to the AC redundancy mechanism.  According to the forwarding state
   machine in table 1 of [I-D.ietf-pals-mpls-tp-dual-homing-protection],
   traffic will be forwarded through the working PW (PW1) and the
   primary AC (AC1).  No traffic will go through the protection PE (PE2)
   or the DNI PW, as both the protection PW (PW2) and the AC connecting
   to PE2 are in standby state.

   If a failure occurs in AC1, the state of AC2 changes to active
   according to the AC redundancy mechanism, while there is no change in
   the state of the working and protection PWs.  According to the
   forwarding state machine in table 1 of
   [I-D.ietf-pals-mpls-tp-dual-homing-protection], PE1 starts to forward
   traffic between the working PW and the DNI PW, and PE2 starts to
   forward traffic between AC2 and the DNI PW.  It should be noted that
   in this case only AC switchover takes place, in the PSN network
   traffic is still forwarded using the working PW.



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   If a failure in the PSN network brings PW1 to down, the failure can
   be detected by PE1 or PE3 using some OAM mechanism.  If PE1 detects
   the failure of PW1, it MUST inform PE2 the state of working PW using
   the PW Status TLV in the DHC messages and change the forwarding
   status of PW1 to standby.  On receipt of the DHC message, PE2 SHOULD
   change the forwarding status of PW2 to active.  Then according to the
   forwarding state machine in table 1 of
   [I-D.ietf-pals-mpls-tp-dual-homing-protection], PE1 SHOULD set up the
   connection between the DNI PW and AC1, and PE2 SHOULD set up the
   connection between PW2 and the DNI PW.  According to the linear
   protection mechanism [RFC6378], PE2 also sends an appropriate
   protection coordination message over the protection PW (PW2) to PE3,
   so that PE3 changes the forwarding status of PW2 to active, thus
   switchover from PW1 to PW2.  If PE3 detects the failure of PW1,
   according to linear protection mechanism [RFC6378], it sends a
   protection coordination message on the protection PW (PW2) to inform
   PE2 of the failure on the working PW.  Upon receipt of the message,
   PE2 SHOULD change the forwarding status of PW2 to active and set up
   the connection according to the forwarding state machine in table 1
   of [I-D.ietf-pals-mpls-tp-dual-homing-protection].  PE2 SHOULD send a
   DHC message to PE1 with the S bit set in the Dual-Node Switching TLV
   to coordinate the switchover on PE1 and PE2.  This could be useful
   for a unidirectional failure which cannot be detected by PE1.

   If a failure brings the working PE (PE1) to down, the failure can be
   detected by both PE2 and PE3 using some OAM mechanisms.  Both PE2 and
   PE3 SHOULD change the forwarding status of PW2 to active, and send a
   protection coordination message on the protection PW (PW2) to inform
   the remote side to switchover.  According to AC redundancy mechanism,
   the status of AC1 changes to standby, and the state of AC2 changes to
   active.  According to the forwarding state machine in table 1 of
   [I-D.ietf-pals-mpls-tp-dual-homing-protection], PE2 starts to forward
   traffic between the PW2 and AC2.

4.  IANA Considerations

   This documnet requests that IANA assigns one new channel type for
   "MPLS-TP Dual-Homing Coordination message" from the "MPLS Generalized
   Associated Channel (G-ACh) Types (including Pseudowire Associated
   Channel Types)" registry of the "Generic Associated Channel (G-ACh)
   Parameters" registry.

   Value  Description                                Reference
   TBD    MPLS-TP Dual-Homing Coordination message   [This document]

   This documnet requests that IANA creates a new sub-registry called
   "MPLS-TP DHC TLVs" in the "Generic Associated Channel (G-ACh)
   Parameters" registry, with fields and initial allocations as follows:



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   Type        Description                 Length       Reference
   0x00        Reserved
   0x01        PW Status                   20 Bytes     [this document]
   0x02        Dual-Node Switching         16 Bytes     [this document]

   The allocation policy for this registry is IETF Review or IESG
   Approval.

5.  Security Considerations

   Procedures and protocol extensions defined in this document do not
   affect the security model of MPLS-TP linear protection as defined in
   [RFC6378].  Please refer to [RFC5920] for MPLS security issues and
   generic methods for securing traffic privacy and integrity.

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>.

   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586,
              DOI 10.17487/RFC5586, June 2009,
              <http://www.rfc-editor.org/info/rfc5586>.

   [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>.

   [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>.






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Internet-Draft  Dual-Homing Coordination for MPLS-TP PWs     August 2016


6.2.  Informative References

   [I-D.ietf-pals-mpls-tp-dual-homing-protection]
              Cheng, W., Wang, L., Li, H., Liu, K., Davari, S., Dong,
              J., and A. D'Alessandro, "Dual-Homing Protection for MPLS
              and MPLS-TP Pseudowires", draft-ietf-pals-mpls-tp-dual-
              homing-protection-03 (work in progress), June 2016.

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
              <http://www.rfc-editor.org/info/rfc5920>.

   [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>.

   [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>.

   [RFC7771]  Malis, A., Ed., Andersson, L., van Helvoort, H., Shin, J.,
              Wang, L., and A. D'Alessandro, "Switching Provider Edge
              (S-PE) Protection for MPLS and MPLS Transport Profile
              (MPLS-TP) Static Multi-Segment Pseudowires", RFC 7771,
              DOI 10.17487/RFC7771, January 2016,
              <http://www.rfc-editor.org/info/rfc7771>.

Authors' Addresses

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

   Email: chengweiqiang@chinamobile.com









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Internet-Draft  Dual-Homing Coordination for MPLS-TP PWs     August 2016


   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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Internet-Draft  Dual-Homing Coordination for MPLS-TP PWs     August 2016


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

   Email: alessandro.dalessandro@telecomitalia.it












































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