[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-ietf-mpls-tp-bfd-cc-cv) 00 01 02 03 04 05 06 RFC 6428

MPLS Working Group                                       Dave Allan, Ed.
Internet Draft                                                 Ericsson
Intended status: Standards Track
Expires: January 2011                                George Swallow Ed.
                                                      Cisco Systems, Inc

                                                          John Drake Ed.

                                                           July 12, 2010

      Proactive Connection Verification, Continuity Check and Remote
               Defect indication for MPLS Transport Profile


   Continuity Check (CC), Proactive Connectivity Verification (CV) and
   Remote Defect Indication (RDI) functionalities required for are MPLS-
   TP OAM.

   Continuity Check monitors the integrity of the continuity of the path
   for any loss of continuity defect. Connectivity verification monitors
   the integrity of the routing of the path between sink and source for
   any connectivity issues. RDI enables an End Point to report, to its
   associated End Point, a fault or defect condition that it detects on
   a PW, LSP or Section.

   This document specifies methods for proactive CV, CC, and RDI for
   MPLS-TP Label Switched Path (LSP), PWs and Sections using
   Bidirectional Forwarding Detection (BFD).

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC2119 [1].

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance
   with the provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet
   Engineering Task Force (IETF), its areas, and its working

Allan et al.,          Expires January 12, 2011                [Page 1]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

   groups.  Note that other groups may also distribute working
   documents as Internet-Drafts.

   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".

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on November 28, 2010.

Copyright Notice

   Copyright (c) 2010 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
   1.1. Authors......................................................4
   2. Conventions used in this document..............................4
   2.1. Terminology..................................................4
   2.2. Issues for discussion........................................4
   3. MPLS CC, proactive CV and RDI Mechanism using BFD..............5
   3.1. ACH code points for CC and proactive CV......................5
   3.2. MPLS BFD CC Message format...................................6
   3.3. MPLS BFD proactive CV Message format.........................6
   3.4. BFD Session in MPLS-TP terminology...........................7
   3.5. BFD Profile for MPLS-TP......................................7
   3.5.1. Session initiation.........................................8
   3.5.2. Defect entry criteria......................................8

Allan et al.,          Expires January 12, 2011                [Page 2]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

   3.5.3. Defect entry consequent action............................10
   3.5.4. Defect exit criteria......................................10
   3.5.5. State machines............................................10
   3.5.6. Configuration of MPLS-TP BFD sessions.....................13
   3.5.7. Discriminator values......................................13
   4. Acknowledgments...............................................13
   5. IANA Considerations...........................................14
   6. Security Considerations.......................................14
   7. References....................................................14
   7.1. Normative References........................................14
   7.2. Informative References......................................15

1. Introduction

   In traditional transport networks, circuits are provisioned on two or
   more switches. Service Providers (SP) need OAM tools to detect mis-
   connectivity and loss of continuity of transport circuits. Both PWs
   and MPLS-TP LSPs [7] emulating traditional transport circuits need to
   provide the same CC and proactive CV capabilities as required in
   draft-ietf-mpls-tp-oam-requirements[3]. This document describes the
   use of BFD for CC, proactive CV, and RDI of a PW, LSP or PST between
   two Maintenance Entity Group End Points (MEPs).

   As described in [9], Continuity Check (CC) and Proactive Connectivity
   Verification (CV) functions are used to detect loss of continuity
   (LOC), and unintended connectivity between two MEPs (e.g. mismerging
   or misconnection or unexpected MEP).

   The Remote Defect Indication (RDI) is an indicator that is
   transmitted by a MEP to communicate to its peer MEP that a signal
   fail condition exists. RDI is only used for bidirectional connections
   and is associated with proactive CC & CV packet generation.

   This document specifies the BFD extension and behavior to satisfy the
   CC, proactive CV monitoring and the RDI functional requirements for
   bi-directional paths. Procedures for uni-directional paths are for
   further study.

   The mechanisms specified in this document are restricted to BFD
   asynchronous mode.

Allan et al.,          Expires January 12, 2011                [Page 3]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

1.1. Authors

David Allan, John Drake, George Swallow, Annamaria Fulignoli, Sami
Boutros, Siva Sivabalan, David Ward, Martin Vigoureux.

2. Conventions used in this document

2.1. Terminology

ACH: Associated Channel Header

BFD: Bidirectional Forwarding Detection

CV: Connection Verification

GAL: Generalized Alert Label

LSR: Label Switching Router

MEG: Maintenance Entity Group

MEP: Maintenance Entity Group End Point

MIP: Maintenance Entity Group Intermediate Point

MPLS-OAM: MPLS Operations, Administration and Maintenance

MPLS-TP: MPLS Transport Profile

MPLS-TP LSP: Uni-directional or Bidirectional Label Switch Path
representing a circuit

MS-PW: Multi-Segment PseudoWire

NMS: Network Management System

PW: Pseudo Wire

RDI: Remote Defect Indication.

TTL: Time To Live

TLV: Type Length Value

2.2. Issues for discussion

   1) Requirement for additional BFD diagnostic codes?

Allan et al.,          Expires January 12, 2011                [Page 4]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

              1. When periodicity of CV cannot be supported

3. MPLS CC, proactive CV and RDI Mechanism using BFD

   This document proposes distinct encapsulations and code points for
   BFD depending on whether the mode of operation is CC or CV:

  o  CC mode: defines a new code point in the Associated Channel Header
     (ACH) described in [2].In this mode Continuity Check and RDI
     functionalities are supported.

  o  CV mode: defines a new code point in the Associated Channel Header
     (ACH) described in [2]. Under MPLS label stack, the ACH with "MPLS
     Proactive CV" code point indicates that the message is an MPLS BFD
     proactive CV and CC message.

  o  RDI: is communicated via the BFD state field in BFD CC and CV
     messages. It is not a distinct PDU.

3.1. ACH code points for CC and proactive CV

    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     |0xHH   BFD CC/CV Code Point    |

       Figure 1: ACH Indication of MPLS-TP Connection Verification

   The first nibble (0001b) indicates the ACH.

   The version and the flags are set to 0 as specified in [2].

   The code point is either

   - BFD CC code point = 0xHH. [HH to be assigned by IANA from the PW
   Associated Channel Type registry.] or,

   - BFD proactive CV code point = 0xHH. [HH to be assigned by IANA from
   the PW Associated Channel Type registry.]

   Both CC and CV modes apply to PWs, MPLS LSPs (including tandem
   connection monitoring), and Sections.

   It's possible to run BFD in CC mode on some transport paths and BFD
   in CV mode on other transport paths. For a given Maintenance Entity
   Group (MEG) only one mode can be used.  A MEP that is configured to

Allan et al.,          Expires January 12, 2011                [Page 5]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

   support CC mode and receives CV BFD packets, or vice versa, MUST
   consider them as an unexpected packet, i.e. detect a mis-connectivity

3.2. MPLS BFD CC Message format

   The format of an MPLS CC Message format 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|     Flags     |    0xHH BFD CC Code point     |
   |                                                               |
   ~                  BFD Control Packet                           ~
   |                                                               |
                     Figure 2: MPLS CC Message

3.3. MPLS BFD proactive CV Message format

   The format of an MPLS CV Message format is shown below, ACH TLVs [5]
   MUST precede the BFD control packet.

    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     |    0xHH  BFD CV Code Point    |
   |                    ACH TLV Header                             |
   |                                                               |
   ~          Unique MEP-ID of source of the BFD packet            ~
   |                                                               |
   |                                                               |
   ~                  BFD Control Packet                           ~
   |                                                               |

                     Figure 3: MPLS CV Message

   As shown in Figure 3, BFD Control packet as defined in [4] is
   transmitted as MPLS labeled packets along with ACH, ACH TLV Header

Allan et al.,          Expires January 12, 2011                [Page 6]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

   defined in Section 3 of RFC 5586 and one ACH TLV object carrying the
   unique MEP Identifier of the source of the BFD packet defined in [8].

   When GAL label is used, the TTL field of the GAL MUST be set to at
   least 1, and the GAL will be the end of stack label (S=1).

3.4. BFD Session in MPLS-TP terminology

   A BFD session corresponds to a CC or a proactive CV OAM instance in
   MPLS-TP terminology.

   A BFD session is enabled when the CC or proactive CV functionality is
   enabled on a configured Maintenance Entity (ME) or in the case of an
   associated bi-directional path, pair of Maintenance Entities.

   On a Sink MEP, a BFD session can be in DOWN, INIT or UP state as
   detailed in [4].

   When on a ME the CC or proactive CV functionality is disabled, the
   BFD session transitions to the ADMIN DOWN State and the BFD session

   A new BFD session is initiated when the operator enables or re-
   enables the CC or CV functionality on the same ME.

3.5. BFD Profile for MPLS-TP

   BFD MUST operate in asynchronous mode. In this mode, the BFD Control
   packets are periodically sent at configurable time rate. This rate is
   typically a fixed value for the lifetime of the session. In the rare
   circumstance where an operator has a reason to change session
   parameters, poll/final discipline is used.

   The transport profile is designed to operate independent of the
   control plane; hence the C bit SHOULD be set.

   This document specifies bi-directional BFD for p2p transport paths,
   hence the M bit MUST be clear.

   There are two modes of operation for bi-directional paths. One in
   which the session state of both directions of the path is coordinated
   and one constructed from BFD sessions in such a way that the two
   directions operate independently. A single bi-directional BFD session
   is used for coordinated operation. Two independent BFD sessions are
   used for independent operation.

   Coordinated operation is as described in [4]. Independent operation
   requires clarification of two aspects of [4]. Independent operation

Allan et al.,          Expires January 12, 2011                [Page 7]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

   is characterized by the setting of MinRxInterval to zero by the MEP
   that is typically the session originator (referred to as the source
   MEP), and there will be a session originator at either end of the bi-
   directional path. Each source MEP will have a corresponding sink MEP
   that has been configured to a Tx interval of zero.

   The base spec is unclear on aspects of how a MEP with a BFD transmit
   rate set to zero behaves. One interpretation is that no periodic
   messages originate with that MEP, it will only originate messages on
   a state change.

   The first clarification is that when a state change occurs a MEP set
   to a transmit rate of zero sends BFD control messages with a one
   second period until such time that the state change is confirmed by
   the session peer. At this point the MEP set to a transmit rate of
   zero can resume quiescent behavior. This adds robustness to all state
   transitions in the RxInterval=0 case.

   The second is that the originating MEP (the one with a non-zero
   TxInterval) will ignore a DOWN state received from a zero interval
   peer. This means that the zero interval peer will continue to send
   DOWN state messages as the state change is never confirmed. This adds
   robustness to the exchange of RDI indication on a uni-directional
   failure (for both session types DOWN with a diagnostic of control
   detection period expired offering RDI functionality).

   A further extension to the base specification is that there are
   additional OAM protocol exchanges that act as inputs to the BFD state
   machine; these are the Link Down Indication [6] and the Lock
   Instruct/Lock Report transactions.

3.5.1. Session initiation

   In all scenarios a BFD session starts with both ends in the DOWN
   state. DOWN state messages exchanged include the desired Tx and Rx
   rates for the session. If a node cannot support the Min Tx rate
   desired by a peer MEP it does not transition from down to the INIT
   state and sends a diagnostic code (TBD) indicating that the requested
   Tx rate cannot be supported.

   Otherwise once a transition from DOWN to INIT has occurred, the
   session progresses as per [4].

3.5.2. Defect entry criteria

   There are further defect criteria beyond that defined in [4] to
   consider given the possibility of mis-connectivity and mis-
   configuration defects. The result is the criteria for a path

Allan et al.,          Expires January 12, 2011                [Page 8]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

   direction to transition from the defect free state to a defect state
   is a superset of that in the BFD base specification [4].
   The following conditions cause a MEP to enter the defect state for CC
   of CV:
     1. BFD session times out (Loss of Continuity defect),
     2. Receipt of a link down indication.
     3. Receipt of an unexpected M bit (Session Mis-configuration

   And the following will cause the MEP to enter the defect state for CV
     1. BFD control packets are received with an unexpected
        encapsulation (Mis-connectivity defect), these include
          - a PW receiving a packet with a GAL
          - an LSP receiving an IP header instead of a GAL
          (note there are other possibilities but these can also alias
     2. Receipt of an unexpected globally unique Source MEP identifier
        (Mis-connectivity defect),
     3. Receipt of an unexpected session discriminator in the your
        discriminator field (Mis-connectivity defect),
     4. Receipt of an expected session discriminator with an unexpected
        label (mis-connectivity defect),

   The effective defect hierarchy (order of checking) is

     1. Receiving nothing

     2. Receiving link down indication

     3. Receiving from an incorrect source (determined by whatever

     4. Receiving from a correct source (as near as can be determined),
        but with incorrect session information)

     5. Receiving control packets in all discernable ways correct.

Allan et al.,          Expires January 12, 2011                [Page 9]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

3.5.3. Defect entry consequent action

   Upon defect entry a sink MEP will assert signal fail into any client
   (sub-)layers. It will also communicate session DOWN to its session

   The blocking of traffic as consequent action MUST be driven only by a
   defect's consequent action as specified in draft-ietf-mpls-tp-oam-
   framework [9] section
   When the defect is mis-branching, the transport path termination will
   silently discard all non-oam traffic received.

3.5.4. Defect exit criteria

   Exit from a Loss of continuity defect

   For a coordinated session, exit from a loss of connectivity defect is
   as described in figure 4 which updates [4].

   For an independent session, exit from a loss of connectivity defect
   occurs upon receipt of a well formed control packet from the peer MEP
   as described in figures 5 and 6.

   Exit from a session mis-configuration defect

   [editors: for a future version of the document]

   Exit from a mis-connectivity defect

   The exit criteria for a mis-connectivity defect is determined by the
   maximum of the set of min Rx session time times the multiplier that
   have been received. A session can transition from DOWN to UP
   (independent mode) or DOWN to INIT (coordinated mode) when both
   correctly formed control packets are being exchanged, and no mis-
   connected control packets have been received in the specified

3.5.5. State machines

   The following state machines update [4]. They have been modified to
   include LDI and LKI as inputs to the state machine and to clarify the
   behavior for independent mode.

   The coordinated session state machine has been augmented to indicate
   LDI and LKR as inputs to the state machine. For a session that is in
   the UP state, receipt of LDI or LKR will transition the session into
   the DOWN state.

Allan et al.,          Expires January 12, 2011               [Page 10]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

   [Dave: I have to think that we do not need to consider LDI/LKR for
   transition from DOWN to INIT, I have to receive a BFD control packet
   to do that which means the condition is cleared, only funky case is
   when I'm getting both UP messages and LDI/LKR]

                             |  | UP, ADMIN DOWN, TIMER, LDI/LKR
                             |  V
               DOWN        +------+  INIT
              +------------|      |------------+
              |            | DOWN |            |
              |  +-------->|      |<--------+  |
              |  |         +------+         |  |
              |  |                          |  |
              |  |               ADMIN DOWN,|  |
              |  |ADMIN DOWN,          DOWN,|  |
              |  |TIMER               TIMER,|  |
              V  |LDI/LKR           LDI/LKR |  V
            +------+                      +------+
       +----|      |                      |      |----+
   DOWN|    | INIT |--------------------->|  UP  |    |INIT, UP
       +--->|      | INIT, UP             |      |<---+
            +------+                      +------+

       Figure 4: State machine for coordinated session operation

   For independent mode, there are two state machines. One for the
   source MEP (who requested MinRxInterval=0) and the sink MEP (who
   agreed to MinRxInterval=0).

   The source MEP will not transition out of the UP state once
   initialized except in the case of a forced ADMIN DOWN. Hence LDI/LKR
   do not enter into the state machine transition from the UP state, but
   do enter into the INIT and DOWN states.

Allan et al.,          Expires January 12, 2011               [Page 11]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

                             |  | UP, ADMIN DOWN, TIMER
                             |  V
               DOWN        +------+  INIT
              +------------|      |------------+
              |            | DOWN |            |
              |  +-------->|      |<--------+  |
              |  |         +------+         |  |
              |  |                          |  |
              |  |               ADMIN DOWN |  |
              |  |ADMIN DOWN,               |  |
              |  |TIMER,                    |  |
              V  |LDI/LKR                   |  V
            +------+                      +------+
       +----|      |                      |      |----+
   DOWN|    | INIT |--------------------->|  UP  |    | INIT, UP, DOWN,
       +--->|      | INIT, UP             |      |<---+ LDI/LKR
            +------+                      +------+

     Figure 5: State machine for source MEP for independent session

   The sink MEP state machine (for which the transmit interval has been
   set to zero) is modified to:

   1) Permit direct transition from DOWN to UP once the session has been
   initialized. With the exception of via the ADMIN DOWN state, the
   source MEP will never transition from the UP state, hence in normal
   unidirectional fault scenarios will never transition to the INIT

Allan et al.,          Expires January 12, 2011               [Page 12]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

                             |  | ADMIN DOWN, TIMER, LDI/LKR
                             |  V
               DOWN        +------+  INIT, UP
              +------------|      |------------+
              |            | DOWN |            |
              |  +-------->|      |<--------+  |
              |  |         +------+         |  |
              |  |                          |  |
              |  |               ADMIN DOWN,|  |
              |  |ADMIN DOWN,    TIMER,     |  |
              |  |TIMER,         DOWN,      |  |
              V  |LDI/LKR        LDI/LKR    |  V
            +------+                      +------+
       +----|      |                      |      |----+
   DOWN|    | INIT |--------------------->|  UP  |    |INIT, UP
       +--->|      | INIT, UP             |      |<---+
            +------+                      +------+

     Figure 6: State machine for the sink MEP for independent session

3.5.6. Configuration of MPLS-TP BFD sessions

   [Editors note, for a future revision of the document]

3.5.7. Discriminator values

   In the BFD control packet the discriminator values have either local
   to the sink MEP or no significance (when not known).

   My Discriminator field MUST be set to a nonzero value (it can be a
   fixed value), the transmitted your discriminator value MUST reflect
   back the received value of My discriminator field or be set to 0 if
   that value is not known.

   Although the BFD base specification permits an implementation to
   change the my discriminator field at arbitrary times, this is not
   permitted for CV mode in order to avoid race conditions in mis-
   connectivity defects.

4. Acknowledgments

   To be added in a later version of this document

Allan et al.,          Expires January 12, 2011               [Page 13]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

5. IANA Considerations

   To be added in a later version of this document

6. Security Considerations

   The security considerations for the authentication TLV need further

   Base BFD foresees an optional authentication section (see [4]
   section 6.7); that can be extended also to the tool proposed in
   this document.

   Authentication methods that require checksum calculation on the
   outgoing packet must extend the checksum also on the ME
   Identifier Section. This is possible but seems uncorrelated with
   the solution proposed in this document: it could be better to
   use the simple password authentication method.

7. References

7.1. Normative References

  [1]   Bradner, S., "Key words for use in RFCs to Indicate
        Requirement Levels", BCP 14, RFC 2119, March 1997.

  [2]   Bocci, M. et al., " MPLS Generic Associated Channel ", RFC
        5586 , June 2009

  [3]   Vigoureux, M., Betts, M. and D. Ward, "Requirements for
        Operations Administration and Maintenance in MPLS
        Transport Networks", RFC5860, May 2010

  [4]   Katz, D. and D. Ward, "Bidirectional Forwarding
        Detection", RFC 5880, June 2010

  [5]   Boutros, S. et al., "Definition of ACH TLV Structure",
        draft-ietf-mpls-tp-ach-tlv-02 (work in progress), March

  [6]   Swallow, G. et al., "MPLS Fault Management OAM", draft-
        ietf-mpls-tp-fault-02 (work in progress), July 2010

Allan et al.,          Expires January 12, 2011               [Page 14]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

7.2. Informative References

  [7]   Bocci, M., et al., "A Framework for MPLS in Transport
        Networks", RFC5921, July 2010

  [8]   Bocci, M. and G. Swallow, "MPLS-TP Identifiers", draft-
        swallow-mpls-tp-identifiers-02 (work in progress), July

  [9]   Allan, D., Busi, I. and B. Niven-Jenkins, "MPLS-TP OAM
        Framework", draft-ietf-mpls-tp-oam-framework-06 (work in
        progress), April 2010

Allan et al.,          Expires January 12, 2011               [Page 15]

Internet-Draft     draft-ietf-mpls-tp-cc-cv-rdi-01            July 2010

   Authors' Addresses

   Dave Allan
   Email: david.i.allan@ericsson.com

   John Drake
   Email: jdrake@juniper.net

   George Swallow
   Cisco Systems, Inc.
   Email: swallow@cisco.com

   Annamaria Fulignoli
   Email: annamaria.fulignoli@ericsson.com

   Sami Boutros
   Cisco Systems, Inc.
   Email: sboutros@cisco.com

   Martin Vigoureux
   Email: martin.vigoureux@alcatel-lucent.com

   Siva Sivabalan
   Cisco Systems, Inc.
   Email: msiva@cisco.com

   David Ward
   Email: dward@juniper.net

Allan et al.,          Expires January 12, 2011               [Page 16]

Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/