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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 2011MPLS Transport Profile Lock Instruct and Loopback FunctionsAbstract   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 Sections7.1.1 and7.1.2 ofRFC 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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6435.Boutros, et al.              Standards Track                    [Page 1]

RFC 6435           MPLS-TP Lock Instruct and Loopback      November 2011Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.   -  The lock function enables an operator to lock a transport path      such that it does not carry client traffic.  As perRFC 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 inRFC 5960 [9]).   -  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 20111.1.  UpdatesRFC 6371   This document updates Sections7.1.1 and7.1.2 ofRFC 6371 [6].   The framework inRFC 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 Conventions2.1.  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 inRFC 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 Live3.  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.  LockBoutros, 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 inSection4.  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 inSection 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 inSection 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:   -  There must be a return path, so the transport path under test must      be bidirectional.   -  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.   -  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   -  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.   -  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.   -  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 Message5.1.  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 Function6.1.  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   inSection 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:   -  If no matching label binding exists, then there is no      corresponding transport path and the received LI message is in      error.   -  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   -  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 (seeSection 6.2 for an explanation of unlocking a MEP).   Note that in some scenarios (such as the use of loopback as described   inSection 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 inSection6.1, 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 Considerations8.1.  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 201110.  References10.1.  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",RFC6371, 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 2011Contributing 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.cnBoutros, et al.              Standards Track                   [Page 11]

RFC 6435           MPLS-TP Lock Instruct and Loopback      November 2011Editors' 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.cnBoutros, et al.              Standards Track                   [Page 12]