GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools

Problem, Formatting or Query -  Send Feedback

Was this page helpful?-10+1


rfc:rfc8185

Internet Engineering Task Force (IETF) W. Cheng Request for Comments: 8185 L. Wang Category: Standards Track H. Li ISSN: 2070-1721 China Mobile

                                                               J. Dong
                                                   Huawei Technologies
                                                       A. D'Alessandro
                                                        Telecom Italia
                                                             June 2017
                      Dual-Homing Coordination
    for MPLS Transport Profile (MPLS-TP) Pseudowires Protection

Abstract

 In some scenarios, MPLS Transport Profile (MPLS-TP) pseudowires (PWs)
 (RFC 5921) may be statically configured when a dynamic control plane
 is not available.  A fast protection mechanism for MPLS-TP PWs is
 needed to protect against the failure of an Attachment Circuit (AC),
 the failure of a Provider Edge (PE), or a failure in the Packet
 Switched Network (PSN).  The framework and typical scenarios of dual-
 homing PW local protection are described in RFC 8184.  This document
 proposes a dual-homing coordination mechanism for MPLS-TP PWs that is
 used for state exchange and switchover coordination between the dual-
 homing PEs for dual-homing PW local protection.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc8185.

Cheng, et al. Standards Track [Page 1] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

Copyright Notice

 Copyright (c) 2017 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
 2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
 3.  Overview of the Proposed Solution . . . . . . . . . . . . . .   4
 4.  Protocol Extensions for Dual-Homing MPLS-TP PW Protection . .   5
   4.1.  Information Exchange Between Dual-Homing PEs  . . . . . .   5
   4.2.  Protection Procedures . . . . . . . . . . . . . . . . . .   9
 5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
 6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
 7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
   7.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
   7.2.  Informative References  . . . . . . . . . . . . . . . . .  15
 Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  16
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

Cheng, et al. Standards Track [Page 2] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

1. Introduction

 [RFC6372], [RFC6378], and [RFC7771] describe the framework and
 mechanism of MPLS Transport Profile (MPLS-TP) linear protection,
 which can provide protection for the MPLS Label Switched Path (LSP)
 and pseudowires (PWs) between the edge nodes.  These mechanisms
 cannot protect against the failure of the Attachment Circuit (AC) or
 the edge nodes.  [RFC6718] and [RFC6870] specify the PW redundancy
 framework and mechanism for protecting the AC or edge node against
 failure by adding one or more edge nodes, but it requires PW
 switchover in case of an AC failure; also, PW redundancy relies on
 Packet Switched Network (PSN) protection mechanisms to protect
 against 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 Customer
 Edge (CE) node on one side is dual-homed to two Provider Edge (PE)
 nodes.  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 AC
 failure in the mobile core site; such massive PW switchover may in
 turn lead to congestion caused by migrating traffic away from the
 preferred paths of 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 the PSN to
 potentially avoid unnecessary switchover for other PWs.  To meet the
 above requirements, a fast dual-homing PW protection mechanism is
 needed to protect against failure in the AC, the PE node, and the
 PSN.
 [RFC8184] describes a framework and several scenarios of dual-homing
 PW local protection.  This document proposes a dual-homing
 coordination mechanism for static MPLS-TP PWs; the mechanism 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 that use static MPLS-TP PWs for the
 backhauling of mobile traffic from the radio access sites to the core
 site.

2. Requirements Language

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in BCP
 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

Cheng, et al. Standards Track [Page 3] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

3. Overview of the Proposed Solution

 Linear protection mechanisms for the 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 against a failure occurring in a PE or a connected AC.  As
 described in [RFC8184], a dedicated Dual-Node Interconnection (DNI)
 PW is used between the two dual-homing PE nodes to forward the
 traffic.  In order to utilize the linear protection mechanism
 [RFC7771] in the dual-homing PEs scenario, coordination between the
 dual-homing PE nodes is needed so that the dual-homing PEs can switch
 the connection between the AC, the service PW, and the DNI-PW
 properly in a coordinated fashion by the forwarder.
       +----------------------------------+
       |                PE1               |
       +----------------------------------+             +----+
       |                 |                |   Working   |    |
       X    Forwarder    +     Service    X-------------X    |
      /|                 |       PW       | Service PW1 |    |
 AC1 / +--------+--------+                |             |    |
    /  |     DNI-PW      |                |             |    |

+—* +——–X——–+—————-+ | | +—+ | | ^ | | | | |CE1| | DNI-PW |PE3 +—|CE2| | | | | | | | | | V | | | | +—* +——–X——–+—————-+ | | +—+

    \  |     DNI-PW      |                |             |    |
 AC2 \ +--------+--------+                | Protection  |    |
      \|                 |     Service    X-------------X    |
       X    Forwarder    +       PW       | Service PW2 |    |
       |                 |                |             +----+
       +----------------------------------+
       |                PE2               |
       +----------------------------------+
             Figure 1: Dual-Homing Protection with DNI-PW

Cheng, et al. Standards Track [Page 4] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

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

 In dual-homing MPLS-TP PW local protection, the forwarding states of
 the dual-homing PEs are determined by the forwarding state machine in
 Table 1.
        +-----------+---------+--------+---------------------+
        |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   |
        +-----------+---------+--------+---------------------+
        |  Active   | Active  |  Down  |Service PW <-> AC    |
        +-----------+---------+--------+---------------------+
        |  Active   | Standby |  Down  |  Drop all packets   |
        +-----------+---------+--------+---------------------+
        |  Standby  | Active  |  Down  |  Drop all packets   |
        +-----------+---------+--------+---------------------+
        |  Standby  | Standby |  Down  |  Drop all packets   |
        +-----------+---------+--------+---------------------+
 Table 1: Dual-Homing PE Forwarding State Machine
 In order to achieve dual-homing MPLS-TP PW protection, coordination
 between the dual-homing PE nodes is needed to exchange the PW status
 and protection coordination requests.

4.1. Information Exchange Between Dual-Homing PEs

 The coordination information will be sent on the DNI-PW over the
 Generic Associated Channel (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 types 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.

Cheng, et al. Standards Track [Page 5] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

 The MPLS-TP Dual-Homing Coordination (DHC) message is sent on the
 DNI-PW between the dual-homing PEs.  The format of the MPLS-TP DHC
 message is shown below:
  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|   Reserved    |         DHC Channel Type      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Dual-Homing PEs Group ID                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         TLV  Length           |           Reserved            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                              TLVs                             ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          Figure 2: MPLS-TP Dual-Homing Coordination Message
 The first 4 octets is the common G-ACh header as specified in
 [RFC5586].  The DHC Channel Type is the G-ACh channel type code point
 assigned by IANA (0x0009).
 The Dual-Homing Group ID is a 4-octet unsigned integer to identify
 the dual-homing group to which the dual-homing PEs belong.  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 the 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.

Cheng, et al. Standards Track [Page 6] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

    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
 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 [RFC6370], which supports both IPv4 and IPv6
 environments.  Usually it is the same as the Label Switching Router
 ID (LSR ID) of the receiver PE.
 The Source Dual-Homing PE Node_ID is the 32-bit identifier of the
 sending PE [RFC6370], which supports both IPv4 and IPv6 environments.
 Usually it is the same as the LSR ID of the sending PE.
 The DNI-PW ID field contains the 32-bit PW ID [RFC8077] 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] on the
    service PW.  It can be either a local request generated by the PE
    itself or a remote request received from the remote PE.

Cheng, et al. Standards Track [Page 7] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

 o  D bit: If set, it indicates Signal Degrade (SD) [RFC6378] 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.
    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 [RFC6370].  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 [RFC6370].  Usually it is the same as the LSR ID of the
 sending PE.
 The DNI-PW ID field contains the 32-bit PW-ID [RFC8077] 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).

Cheng, et al. Standards Track [Page 8] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

 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 it 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 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 as quickly as possible to allow for fast
 protection switching using three consecutive DHC messages.  This set
 of three messages allows for fast protection switching even if one or
 two of these packets are lost or corrupted.  After the transmission
 of the three rapid messages, the dual-homing PE MUST send the most
 recently transmitted service PW status periodically to the other
 dual-homing PE on a continual basis using the 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 as quickly as
 possible to allow for fast protection switching using three
 consecutive DHC messages.  After the transmission of the three
 messages, the protection PW would become the active service PW, and
 the dual-homing PE MUST send the most recently transmitted Dual-Node
 Switching TLV periodically to the other dual-homing PE on a continual
 basis using the DHC message.
 It is RECOMMENDED that the default interval of the first three rapid
 DHC messages be 3.3 ms, similar to [RFC6378], and the default
 interval of the subsequent messages is 1 second.  Both the default
 interval of the three consecutive messages as well as the default
 interval of the periodic messages SHALL be configurable by the
 operator.

4.2. Protection Procedures

 The dual-homing MPLS-TP PW protection mechanism can be deployed with
 the existing AC redundancy mechanisms.  On the PSN side, a PSN tunnel
 protection mechanism is not required, as the dual-homing PW
 protection can also protect if a failure occurs in the PSN.
 This section uses the one-side dual-homing scenario as an example to
 describe the dual-homing PW protection procedures; the procedures for
 a two-side dual-homing scenario would be similar.

Cheng, et al. Standards Track [Page 9] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

 On the dual-homing PE side, the role of working and protection PE are
 set by the management system 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 the single-homing PE side, it 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:
           +---------------------------------+          +-----+
           |        PE1 (Working PE)         |          |     |
           +---------------------------------+    PW1   |     |
           |                 |               |  Working |     |
           +    Forwarder    +    Service    X<-------->X     |
          /|                 |      PW       |          |     |
         / +--------+--------+               |          |     |
   AC1  /  |     DNI-PW      |               |          |     |
       /   +--------X--------+---------------+          |     |

+—–+/ AC ^ DNI-PW | | +—+ | CE1 |redundancy | | PE3 +–|CE2| +—–+ mechanism | DHC message | | +—+

      \             V   exchange                        |     |
   AC2 \   +--------X--------+---------------+          |     |
        \  |     DNI-PW      |               |          |     |
         \ +--------+--------+               |    PW2   |     |
          \|                 |     Service   |Protection|     |
           +    Forwarder    +       PW      X<-------->X     |
           |                 |               |   PSC    |     |
           +---------------------------------+  message |     |
           |        PE2 (Protection PE)      | exchange |     |
           +---------------------------------+          +-----+
      Figure 5: Components of One-Side Dual-Homing PW Protection
 In Figure 5, for each dual-homing PE, the 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 Operation,
 Administration, and Maintenance (OAM) mechanisms between the dual-
 homing PEs and the remote PE.
 The DNI-PW is provisioned between the two dual-homing PE nodes.  It
 is used to bridge traffic when a failure occurs in the PSN or in the
 ACs.  The state of the DNI-PW is determined by the OAM mechanism
 between the dual-homing PEs.  Since the DNI-PW is used to carry both

Cheng, et al. Standards Track [Page 10] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

 the DHC 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 underlying Label Switched Path (LSP)
 protection mechanism SHOULD be enabled.
 The AC is the link that connects a dual-homing PE to the dual-homed
 CE.  The status of AC is determined by the existing AC redundancy
 mechanisms; this 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 in
 Section 4.1.
 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 the three consecutive DHC messages.
 After the transmission of the three rapid messages, the dual-homing
 PE MUST send the most recently transmitted service PW status
 periodically to the other dual-homing PE on a continual basis using
 the DHC message.  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 the
 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 the three consecutive 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 the DNI-PW is
 determined by PW OAM mechanism as defined in [RFC5085], and the
 status of ACs is determined by existing AC redundancy mechanisms:
 both are 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.

Cheng, et al. Standards Track [Page 11] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

 Using 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, 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, 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, traffic is still
 forwarded using the working PW.
 If a failure in the PSN brings PW1 down, the failure can be detected
 by PE1 or PE3 using existing OAM mechanisms.  If PE1 detects the
 failure of PW1, it MUST inform PE2 of the state of the 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, 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 [RFC6378] over the protection PW
 (PW2) to PE3 for the remote side to switchover from PW1 to PW2.  If
 PE3 detects the failure of PW1, according to the 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.  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 is useful for a
 unidirectional failure that cannot be detected by PE1.
 If a failure brings the working PE (PE1) down, the failure can be
 detected by both PE2 and PE3 using existing OAM mechanisms.  Both PE2
 and PE3 SHOULD change the forwarding status of PW2 to active and send
 a protection coordination message [RFC6378] on the protection PW
 (PW2) to inform the remote side to switchover.  According to the
 existing AC redundancy mechanisms, the status of AC1 changes to

Cheng, et al. Standards Track [Page 12] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

 standby and the state of AC2 changes to active.  According to the
 forwarding state machine in Table 1, PE2 starts to forward traffic
 between the PW2 and AC2.

5. IANA Considerations

 IANA has assigned a new channel type for the "MPLS-TP Dual-Homing
 Coordination Message" from the "MPLS Generalized Associated Channel
 (G-ACh) Types (including Pseudowire Associated Channel Types)"
 subregistry within the "Generic Associated Channel (G-ACh)
 Parameters" registry.
 Value     Description                                Reference
 0x0009    MPLS-TP Dual-Homing Coordination message   RFC 8185
 IANA has created a new subregistry called "MPLS-TP DHC TLVs" within
 the "Generic Associated Channel (G-ACh) Parameters" registry.  The
 registry has the following fields and initial allocations:
 Type        Description                 Length       Reference
 0x0000      Reserved
 0x0001      PW Status                   20 Bytes     RFC 8185
 0x0002      Dual-Node Switching         16 Bytes     RFC 8185
 The allocation policy for this registry is IETF Review, as specified
 in [RFC8126].

6. Security Considerations

 MPLS-TP is a subset of MPLS and so builds upon many of the aspects of
 the MPLS security model.  Please refer to [RFC5920] for generic MPLS
 security issues and methods for securing traffic privacy and
 integrity.
 The DHC message defined in this document contains control
 information.  If it is injected or modified by an attacker, the dual-
 homing PEs might not agree on which PE should be used to deliver the
 CE traffic, and this could be used as a denial-of-service attack
 against the CE.  It is important that the DHC message be used within
 a trusted MPLS-TP network domain as described in [RFC6941].
 The DHC message is carried in the G-ACh [RFC5586], so it is dependent
 on the security of the G-ACh itself.  The G-ACh is a generalization
 of the Associated Channel defined in [RFC4385].  Thus, this document
 relies on the security mechanisms provided for the Associated Channel
 as described in those two documents.

Cheng, et al. Standards Track [Page 13] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

 As described in the Security Considerations section of [RFC6378], the
 G-ACh is essentially connection oriented, so injection or
 modification of control messages requires the subversion of a transit
 node.  Such subversion is generally considered hard in connection-
 oriented MPLS networks and impossible to protect against at the
 protocol level.  Management-level techniques are more appropriate.
 The procedures and protocol extensions defined in this document do
 not affect the security model of MPLS-TP linear protection as defined
 in [RFC6378].
 Uniqueness of the identifiers defined in this document is guaranteed
 by the assigner (e.g., the operator).  Failure by an assigner to use
 unique values within the specified scoping for any of the identifiers
 defined herein could result in operational problems.  Please refer to
 [RFC6370] for more details about the uniqueness of the identifiers.

7. References

7.1. 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>.
 [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>.
 [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>.
 [RFC6370]  Bocci, M., Swallow, G., and E. Gray, "MPLS Transport
            Profile (MPLS-TP) Identifiers", RFC 6370,
            DOI 10.17487/RFC6370, September 2011,
            <http://www.rfc-editor.org/info/rfc6370>.
 [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>.

Cheng, et al. Standards Track [Page 14] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

 [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>.
 [RFC8077]  Martini, L., Ed. and G. Heron, Ed., "Pseudowire Setup and
            Maintenance Using the Label Distribution Protocol (LDP)",
            STD 84, RFC 8077, DOI 10.17487/RFC8077, February 2017,
            <http://www.rfc-editor.org/info/rfc8077>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <http://www.rfc-editor.org/info/rfc8174>.

7.2. Informative References

 [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,
            "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
            Use over an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385,
            February 2006, <http://www.rfc-editor.org/info/rfc4385>.
 [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>.

Cheng, et al. Standards Track [Page 15] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

 [RFC6941]  Fang, L., Ed., Niven-Jenkins, B., Ed., Mansfield, S., Ed.,
            and R. Graveman, Ed., "MPLS Transport Profile (MPLS-TP)
            Security Framework", RFC 6941, DOI 10.17487/RFC6941, April
            2013, <http://www.rfc-editor.org/info/rfc6941>.
 [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>.
 [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
            Writing an IANA Considerations Section in RFCs", BCP 26,
            RFC 8126, DOI 10.17487/RFC8126, June 2017,
            <http://www.rfc-editor.org/info/rfc8126>.
 [RFC8184]  Cheng, W., Wang, L., Li, H., Davari, S., and J. Dong,
            "Dual-Homing Protection for MPLS and the MPLS Transport
            Profile (MPLS-TP) Pseudowires", RFC 8184,
            DOI 10.17487/RFC8184, June 2017.

Contributors

 The following individuals substantially contributed to the content of
 this document:
 Kai Liu
 Huawei Technologies
 Email: alex.liukai@huawei.com
 Shahram Davari
 Broadcom Corporation
 Email: davari@broadcom.com

Cheng, et al. Standards Track [Page 16] RFC 8185 Dual-Homing Coordination for MPLS-TP PWs June 2017

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
 Jie Dong
 Huawei Technologies
 Huawei Campus, No. 156 Beiqing Rd.
 Beijing  100095
 China
 Email: jie.dong@huawei.com
 Alessandro D'Alessandro
 Telecom Italia
 via Reiss Romoli, 274
 Torino  10148
 Italy
 Email: alessandro.dalessandro@telecomitalia.it

Cheng, et al. Standards Track [Page 17]

/data/webs/external/dokuwiki/data/pages/rfc/rfc8185.txt · Last modified: 2017/06/26 19:32 (external edit)