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rfc:rfc6435

Internet Engineering Task Force (IETF) S. Boutros, Ed. Request for Comments: 6435 S. Sivabalan, Ed. Updates: 6371 Cisco Systems, Inc. Category: Standards Track R. Aggarwal, Ed. ISSN: 2070-1721 Arktan, Inc.

                                                     M. Vigoureux, Ed.
                                                        Alcatel-Lucent
                                                           X. Dai, Ed.
                                                       ZTE Corporation
                                                         November 2011
    MPLS Transport Profile Lock Instruct and Loopback Functions

Abstract

 Two useful Operations, Administration, and Maintenance (OAM)
 functions in a transport network are "lock" and "loopback".  The lock
 function enables an operator to lock a transport path such that it
 does not carry client traffic, but can continue to carry OAM messages
 and may carry test traffic.  The loopback function allows an operator
 to set a specific node on the transport path into loopback mode such
 that it returns all received data.
 This document specifies the lock function for MPLS networks and
 describes how the loopback function operates in MPLS networks.
 This document updates Sections 7.1.1 and 7.1.2 of RFC 6371.

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 5741.
 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/rfc6435.

Boutros, et al. Standards Track [Page 1] RFC 6435 MPLS-TP Lock Instruct and Loopback November 2011

Copyright Notice

 Copyright (c) 2011 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.

1. Introduction

 Two useful Operations, Administration, and Maintenance (OAM)
 functions in a transport network are "lock" and "loopback".  This
 document discusses these functions in the context of MPLS networks.
  1. The lock function enables an operator to lock a transport path

such that it does not carry client traffic. As per RFC 5860 [1],

    lock is an administrative state in which it is expected that no
    client traffic may be carried.  However, test traffic and OAM
    messages can still be mapped onto the locked transport path.  The
    lock function may be applied to the Label Switched Paths (LSPs),
    Pseudowires (PWs) (including multi-segment Pseudowires) (MS-PWs),
    and bidirectional MPLS Sections as defined in RFC 5960 [9]).
  1. The loopback function allows an operator to set a specific node on

a transport path into loopback mode such that it returns all

    received data.  Loopback can be applied at a Maintenance Entity
    Group End Point (MEP) or a Maintenance Entity Group Intermediate
    Point (MIP) on a co-routed bidirectional LSP, on a PW, or on a
    bidirectional MPLS Section.  It can also be applied at a MEP on an
    associated bidirectional LSP.
    Loopback is used to test the integrity of the transport path to
    and from the node that is performing loopback.  It requires that
    the transport path be locked and that a MEP on the transport path
    send test data that it also validates on receipt.
 This document specifies the lock function for MPLS networks and
 describes how the loopback function operates in MPLS networks.

Boutros, et al. Standards Track [Page 2] RFC 6435 MPLS-TP Lock Instruct and Loopback November 2011

1.1. Updates RFC 6371

 This document updates Sections 7.1.1 and 7.1.2 of RFC 6371 [6].
 The framework in RFC 6371 makes the assumption that the Lock Instruct
 message is used to independently enable locking and requires a
 response message.
 The mechanism defined in this document requires that when a lock
 instruction is sent by management to both ends of the locked
 transport path, the Lock Instruct message does not require a
 response.

2. Terminology and Conventions

2.1. Conventions Used in This Document

 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 [2].

2.2. Acronyms and Terms

 ACH: Associated Channel Header
 LI: Lock Instruct
 MEG: Maintenance Entity Group
 MEP: Maintenance Entity Group End Point
 MIP: Maintenance Entity Group Intermediate Point
 MPLS-TP: MPLS Transport Profile
 NMS: Network Management System
 TLV: Type Length Value
 Transport path: MPLS-TP LSP or PW
 TTL: Time To Live

3. Lock Function

 Lock is used to request that a MEP take a transport path out of
 service for administrative reasons.  For example, Lock can be used to
 allow some form of maintenance to be done for a transport path.  Lock

Boutros, et al. Standards Track [Page 3] RFC 6435 MPLS-TP Lock Instruct and Loopback November 2011

 is also a prerequisite of the loopback function described in Section
 4.  The NMS or a management process initiates a Lock by sending a
 Lock command to a MEP.  The MEP takes the transport path out of
 service, that is, it stops injecting or forwarding traffic onto the
 transport path.
 To properly lock a transport path (for example, to ensure that a
 loopback test can be performed), both directions of the transport
 path must be taken out of service; therefore, a Lock command is sent
 to the MEPs at both ends of the path.  This ensures that no traffic
 is sent in either direction.  Thus, the lock function can be realized
 entirely using the management plane.
 However, dispatch of messages in the management plane to the two MEPs
 may present coordination challenges.  It is desirable that the lock
 be achieved in a coordinated way within a tight window, and this may
 be difficult with a busy management plane.  In order to provide
 additional coordination, an LI OAM message can also be sent.  A MEP
 locks a transport path when it receives a command from a management
 process or when it receives an LI message as described in Section 6.
 This document defines an LI message for MPLS OAM.  The LI message is
 based on a new ACH Type as well as an existing TLV.  This is a common
 mechanism applicable to lock LSPs, PWs, and bidirectional MPLS
 Sections.

4. Loopback Function

 This section provides a description of the loopback function within
 an MPLS network.  This function is achieved through management
 commands, so there is no protocol specification necessary.  However,
 the loopback function is dependent on the lock function, so it is
 appropriate to describe it in this document.
 The loopback function is used to test the integrity of a transport
 path from a MEP up any other node in the same MEG.  This is achieved
 by setting the target node into loopback mode, and transmitting a
 pattern of test data from the MEP.  The target node loops all
 received data back toward the originator, and the MEP extracts the
 test data and compares it with what it sent.
 Loopback is a function that enables a receiving MEP or MIP to return
 traffic to the sending MEP when in the loopback state.  This state
 corresponds to the situation where, at a given node, a forwarding
 plane loop is configured, and the incoming direction of a transport
 path is cross-connected to the outgoing reverse direction.
 Therefore, except in the case of early TTL expiry, traffic sent by
 the source will be received by that source.

Boutros, et al. Standards Track [Page 4] RFC 6435 MPLS-TP Lock Instruct and Loopback November 2011

 Data-plane loopback is an out-of-service function, as required in
 Section 2.2.5 of RFC 5860 [1].  This function loops back all traffic
 (including user data and OAM).  The traffic can be originated from
 one internal point at the ingress of a transport path within an
 interface or inserted from an input port of an interface using
 external test equipment.  The traffic is looped back unmodified
 (other than normal per-hop processing such as TTL decrement) in the
 direction of the point of origin by an interface at either an
 intermediate node or a terminating node.
 It should be noted that the data-plane loopback function itself is
 applied to data-plane loopback points residing on different
 interfaces from MIPs/MEPs.  All traffic (including both payload and
 OAM) received on the looped back interface is sent on the reverse
 direction of the transport path.
 For data-plane loopback at an intermediate point in a transport path,
 the loopback needs to be configured to occur at either the ingress or
 egress interface.  This is done using management.
 The management plane can be used to configure the loopback function.
 The management plane must ensure that the two MEPs are locked before
 it requests setting MEP or MIP in the loopback state.
 The nature of test data and the use of loopback traffic to measure
 packet loss, delay, and delay variation are outside the scope of this
 document.

4.1. Operational Prerequisites

 Obviously, for the loopback function to operate, there are several
 prerequisites:
  1. There must be a return path, so the transport path under test must

be bidirectional.

  1. The node in loopback mode must be on both the forward and return

paths. This is possible for all MEPs and MIPs on a co-routed

    bidirectional LSP, on a PW, or on a bidirectional MPLS Section,
    but it is only possible for MEPs on associated bidirectional LSPs.
  1. The transport path cannot deliver client data when one of its

nodes is in loopback mode, so it is important that the transport

    path be locked before loopback is enabled.

Boutros, et al. Standards Track [Page 5] RFC 6435 MPLS-TP Lock Instruct and Loopback November 2011

  1. Management-plane coordination between the node in loopback mode

and the MEP sending test data is required. The MEP must not send

    test data until loopback has been properly configured because this
    would result in the test data continuing toward the destination.
  1. The TTL of the test packets must be set sufficiently large to

account for both directions of the transport path under test;

    otherwise, the packets will not be returned to the originating
    MEP.
  1. OAM messages intended for delivery to nodes along the transport

path under test can be delivered by correct TTL expiry. However,

    OAM messages cannot be delivered to points beyond the loopback
    node until the loopback condition is lifted.

5. Lock Instruct Message

5.1. Message Identification

 The Lock Instruct message is carried in the Generic ACH described in
 [4].  It is identified by a new PW ACH Type of 0x0026.

5.2. LI Message Format

 The format of an LI 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Vers  | Reserved                              | Refresh Timer |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        MEP Source ID TLV                      |
 ~                                                               ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          Figure 1: MPLS Lock Instruct Message Format
 Version: The Version number is currently 1.  (Note: the version
 number is to be incremented whenever a change is made that affects
 the ability of an implementation to correctly parse or process the
 message.  These changes include any syntactic or semantic changes
 made to any of the fixed fields, or to any Type-Length-Value (TLV) or
 sub- TLV assignment or format that is defined at a certain version
 number.  The version number may not need to be changed if an optional
 TLV or sub-TLV is added.)
 Reserved: The Reserved field MUST be set to zero on transmission and
 SHOULD be ignored on receipt.

Boutros, et al. Standards Track [Page 6] RFC 6435 MPLS-TP Lock Instruct and Loopback November 2011

 Refresh Timer: The Refresh Timer is the maximum time between
 successive LI messages specified in seconds.  The default value is 1.
 The value 0 is not permitted.  When a lock is applied, a refresh
 timer is chosen.  This value MUST NOT be changed for the duration of
 that lock.  A node receiving an LI message with a changed refresh
 timer MAY ignore the new value and continue to apply the old value.
 MEP Source ID TLV: This is one of the three MEP Source ID TLVs
 defined in [3] and identifies the MEP that originated the LI message.

6. Operation of the Lock Function

6.1. Locking a Transport Path

 When a MEP receives a Lock command from an NMS or through some other
 management process, it MUST take the transport path out of service.
 That is, it MUST stop injecting or forwarding traffic onto the LSP,
 PW, or bidirectional Section that has been locked.
 If rapid coordination of lock state is to be achieved (as described
 in Section 3) then as soon as the transport path has been locked, the
 MEP MUST send an LI message targeting the MEP at the other end of the
 locked transport path. In this case, the source MEP MUST set the
 Refresh Timer value in the LI message and MUST retransmit the LI
 message at the frequency indicated by the value set.
 When locking a transport path, the NMS or management process is
 required to send a Lock command to both ends of the transport path.
 Thus, a MEP may receive either the management command or an LI
 message first.  A MEP MUST take the transport path out of service
 immediately in either case, but sends LI messages itself after it has
 received a management Lock command.  Thus, a MEP is locked if either
 Lock was requested by management (and, as a result, the MEP is
 sending LI messages) or it is receiving LI messages from the remote
 MEP.
 Note that a MEP that receives an LI message MUST identify the correct
 transport path and validate the message.  The label stack on the
 received message is used to identify the transport path to be locked:
  1. If no matching label binding exists, then there is no

corresponding transport path and the received LI message is in

    error.
  1. If the transport path can be identified, but there is no return

path (for example, the transport path was unidirectional) then

    (obviously) the receiving MEP cannot apply a lock to the return
    path.

Boutros, et al. Standards Track [Page 7] RFC 6435 MPLS-TP Lock Instruct and Loopback November 2011

  1. If the transport path is suitable for locking but the Source MEP-

ID identifies an unexpected MEP for the MEG to which the receiving

    MEP belongs, the received LI message is in error.
 When an errored LI message is received, the receiving MEP MUST NOT
 apply a lock.  A MEP receiving errored LI messages SHOULD perform
 local diagnostic actions (such as counting the messages) and MAY log
 the messages.
 A MEP keeps a transport path locked as long as it is either receiving
 the periodic LI messages or has an in-force Lock command from
 management (see Section 6.2 for an explanation of unlocking a MEP).
 Note that in some scenarios (such as the use of loopback as described
 in Section 4), LI messages will not continue to be delivered on a
 locked transport path.  This is why a transport path is considered
 locked while there is an in-force Lock command from a management
 process regardless of whether LI messages are being received.

6.2. Unlocking a Transport Path

 Unlock is used to request that a MEP bring the previously locked
 transport path back in service.
 When a MEP receives an Unlock command from a management process, it
 MUST cease sending LI messages.  However, as described in Section
 6.1, if the MEP is still receiving LI messages, the transport path
 MUST remain out of service.  Thus, to unlock a transport path, the
 management process has to send an Unlock command to the MEPs at both
 ends.
 When a MEP has been unlocked and has not received an LI message for a
 multiple of 3.5 times the Refresh Timer on the LI message (or has
 never received an LI message), the MEP unlocks the transport path and
 puts it back into service.

7. Security Considerations

 MPLS-TP is a subset of MPLS and builds upon many of the aspects of
 the security model of MPLS.  MPLS networks make the assumption that
 it is very hard to inject traffic into a network, and it is equally
 hard to cause traffic to be directed outside the network.  For more
 information on the generic aspects of MPLS security, see [7].
 This document describes a protocol carried in the G-ACh [4], so it is
 dependent on the security of the G-ACh, itself.  The G-ACh is a
 generalization of the Pseudowire Associated Channel defined in [8].
 Thus, this document relies heavily on the security mechanisms
 provided for the Associated Channel as described in [4] and [8].

Boutros, et al. Standards Track [Page 8] RFC 6435 MPLS-TP Lock Instruct and Loopback November 2011

 A specific concern for the G-ACh is that is can be used to provide a
 covert channel.  This problem is wider than the scope of this
 document and does not need to be addressed here, but it should be
 noted that the channel provides end-to-end connectivity and SHOULD
 NOT be policed by transit nodes.  Thus, there is no simple way to
 prevent traffic from being carried in the G-ACh between consenting
 nodes.
 A good discussion of the data-plane security of an associated channel
 may be found in [5].  That document also describes some mitigation
 techniques.
 It should be noted that the G-ACh is essentially connection-oriented,
 so injection or modification of control messages specified in this
 document requires the subversion of a transit node.  Such subversion
 is generally considered hard in MPLS networks, and impossible to
 protect against at the protocol level.  Management-level techniques
 are more appropriate.

8. IANA Considerations

8.1. Pseudowire Associated Channel Type

 LI OAM requires a unique Associated Channel Type that has been
 assigned by IANA in the "Pseudowire Associated Channel Types"
 registry.
 Registry:
    Value        Description              TLV Follows  Reference
    -----------  -----------------------  -----------  ---------
    0x0026       LI                       No           [RFC6435]

9. Acknowledgements

 The authors would like to thank Loa Andersson, Yoshinori Koike,
 Alessandro D'Alessandro Gerardo, Shahram Davari, Greg Mirsky, Yaacov
 Weingarten, Liu Guoman, Matthew Bocci, Adrian Farrel, and Jia He for
 their valuable comments.

Boutros, et al. Standards Track [Page 9] RFC 6435 MPLS-TP Lock Instruct and Loopback November 2011

10. References

10.1. Normative References

 [1] Vigoureux, M., Ed., Ward, D., Ed., and M. Betts, Ed.,
     "Requirements for Operations, Administration, and Maintenance
     (OAM) in MPLS Transport Networks", RFC 5860, May 2010.
 [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Levels", BCP 14, RFC 2119, March 1997.
 [3] Allan, D., Ed., Swallow, G., Ed., and J. Drake, Ed., "Proactive
     Connectivity Verification, Continuity Check, and Remote Defect
     Indication for the MPLS Transport Profile", RFC 6428, November
     2011.
 [4] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., "MPLS
     Generic Associated Channel", RFC 5586, June 2009.
 [5] Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire Virtual
     Circuit Connectivity Verification (VCCV): A Control Channel for
     Pseudowires", RFC 5085, December 2007.
 [6] Busi, I., Ed., and D. Allan, Ed., "Operations, Administration,
     and Maintenance Framework for MPLS-Based Transport Networks", RFC
     6371, September 2011.

10.2. Informative References

 [7] Fang, L., Ed., "Security Framework for MPLS and GMPLS Networks",
     RFC 5920, July 2010.
 [8] 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, February 2006.
 [9] Frost, D., Ed., Bryant, S., Ed., and M. Bocci, Ed., "MPLS
     Transport Profile Data Plane Architecture", RFC 5960, August
     2010.

Boutros, et al. Standards Track [Page 10] RFC 6435 MPLS-TP Lock Instruct and Loopback November 2011

Contributing Authors

 George Swallow
 Cisco Systems, Inc.
 EMail: swallow@cisco.com
 David Ward
 Juniper Networks.
 EMail: dward@juniper.net
 Stewart Bryant
 Cisco Systems, Inc.
 EMail: stbryant@cisco.com
 Carlos Pignataro
 Cisco Systems, Inc.
 EMail: cpignata@cisco.com
 Eric Osborne
 Cisco Systems, Inc.
 EMail: eosborne@cisco.com
 Nabil Bitar
 Verizon.
 EMail: nabil.bitar@verizon.com
 Italo Busi
 Alcatel-Lucent.
 EMail: italo.busi@alcatel-lucent.com
 Lieven Levrau
 Alcatel-Lucent.
 EMail: lieven.levrau@alcatel-lucent.com
 Laurent Ciavaglia
 Alcatel-Lucent.
 EMail: laurent.ciavaglia@alcatel-lucent.com
 Bo Wu
 ZTE Corporation.
 EMail: wu.bo@zte.com.cn
 Jian Yang
 ZTE Corporation.
 EMail: yang_jian@zte.com.cn

Boutros, et al. Standards Track [Page 11] RFC 6435 MPLS-TP Lock Instruct and Loopback November 2011

Editors' Addresses

 Sami Boutros
 Cisco Systems, Inc.
 EMail: sboutros@cisco.com
 Siva Sivabalan
 Cisco Systems, Inc.
 EMail: msiva@cisco.com
 Rahul Aggarwal
 Arktan, Inc
 EMail: raggarwa_1@yahoo.com
 Martin Vigoureux
 Alcatel-Lucent.
 EMail: martin.vigoureux@alcatel-lucent.com
 Xuehui Dai
 ZTE Corporation.
 EMail: dai.xuehui@zte.com.cn

Boutros, et al. Standards Track [Page 12]

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