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rfc:rfc6426

Internet Engineering Task Force (IETF) E. Gray Request for Comments: 6426 Ericsson Updates: 4379 N. Bahadur Category: Standards Track Juniper Networks, Inc. ISSN: 2070-1721 S. Boutros

                                                   Cisco Systems, Inc.
                                                           R. Aggarwal
                                                         November 2011
     MPLS On-Demand Connectivity Verification and Route Tracing

Abstract

 Label Switched Path Ping (LSP ping) is an existing and widely
 deployed Operations, Administration, and Maintenance (OAM) mechanism
 for Multi-Protocol Label Switching (MPLS) Label Switched Paths
 (LSPs).  This document describes extensions to LSP ping so that LSP
 ping can be used for on-demand connectivity verification of MPLS
 Transport Profile (MPLS-TP) LSPs and pseudowires.  This document also
 clarifies procedures to be used for processing the related OAM
 packets.  Further, it describes procedures for using LSP ping to
 perform connectivity verification and route tracing functions in
 MPLS-TP networks.  Finally, this document updates RFC 4379 by adding
 a new address type and creating an IANA registry.

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/rfc6426.

Gray, et al. Standards Track [Page 1] RFC 6426 MPLS On-Demand Connectivity Verification 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.

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.1.  Conventions Used in This Document  . . . . . . . . . . . .  3
   1.2.  On-Demand CV for MPLS-TP LSPs Using IP Encapsulation . . .  4
   1.3.  On-Demand CV for MPLS-TP LSPs Using Non-IP
         Encapsulation  . . . . . . . . . . . . . . . . . . . . . .  4
 2.  LSP Ping Extensions  . . . . . . . . . . . . . . . . . . . . .  5
   2.1.  New Address Type for Downstream Mapping TLV  . . . . . . .  5
     2.1.1.  DSMAP/DDMAP Non-IP Address Information . . . . . . . .  5
   2.2.  Source/Destination Identifier TLV  . . . . . . . . . . . .  7
     2.2.1.  Source/Destination Identifier TLV Format . . . . . . .  7
     2.2.2.  Source Identifier TLV  . . . . . . . . . . . . . . . .  7
     2.2.3.  Destination Identifier TLV . . . . . . . . . . . . . .  8
   2.3.  Identifying Statically Provisioned LSPs and PWs  . . . . .  8
     2.3.1.  Static LSP Sub-TLV . . . . . . . . . . . . . . . . . .  9
     2.3.2.  Static Pseudowire Sub-TLV  . . . . . . . . . . . . . . 10
 3.  Performing On-Demand CV over MPLS-TP LSPs  . . . . . . . . . . 10
   3.1.  LSP Ping with IP Encapsulation . . . . . . . . . . . . . . 11
   3.2.  On-Demand CV with IP Encapsulation, over ACH . . . . . . . 11
   3.3.  Non-IP-Based On-Demand CV, Using ACH . . . . . . . . . . . 12
   3.4.  Reverse-Path Connectivity Verification . . . . . . . . . . 13
     3.4.1.  Requesting Reverse-Path Connectivity Verification  . . 13
     3.4.2.  Responder Procedures . . . . . . . . . . . . . . . . . 13
     3.4.3.  Requester Procedures . . . . . . . . . . . . . . . . . 14
   3.5.  P2MP Considerations  . . . . . . . . . . . . . . . . . . . 14
   3.6.  Management Considerations for Operation with Static
         MPLS-TP  . . . . . . . . . . . . . . . . . . . . . . . . . 14
   3.7.  Generic Associated Channel Label (GAL) Processing  . . . . 14
 4.  Performing On-Demand Route Tracing over MPLS-TP LSPs . . . . . 15
   4.1.  On-Demand LSP Route Tracing with IP Encapsulation  . . . . 15

Gray, et al. Standards Track [Page 2] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

   4.2.  Non-IP-Based On-Demand LSP Route Tracing, Using ACH  . . . 15
     4.2.1.  Requester Procedure for Sending Echo Request
             Packets  . . . . . . . . . . . . . . . . . . . . . . . 16
     4.2.2.  Requester Procedure for Receiving Echo Response
             Packets  . . . . . . . . . . . . . . . . . . . . . . . 16
     4.2.3.  Responder Procedure  . . . . . . . . . . . . . . . . . 16
   4.3.  P2MP Considerations  . . . . . . . . . . . . . . . . . . . 16
   4.4.  ECMP Considerations  . . . . . . . . . . . . . . . . . . . 16
 5.  Applicability  . . . . . . . . . . . . . . . . . . . . . . . . 16
 6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
 7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   7.1.  New Source and Destination Identifier TLVs . . . . . . . . 17
   7.2.  New Target FEC Stack Sub-TLVs  . . . . . . . . . . . . . . 17
   7.3.  New Reverse-Path Target FEC Stack TLV  . . . . . . . . . . 18
   7.4.  New Pseudowire Associated Channel Type . . . . . . . . . . 18
   7.5.  New Downstream Mapping Address Type Registry . . . . . . . 18
 8.  Contributing Authors and Acknowledgements  . . . . . . . . . . 19
 9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
   9.1.  Normative References . . . . . . . . . . . . . . . . . . . 20
   9.2.  Informative References . . . . . . . . . . . . . . . . . . 20

1. Introduction

 Label Switched Path Ping (LSP ping) [RFC4379] is an Operations,
 Administration, and Maintenance (OAM) mechanism for Multi-Protocol
 Label Switching (MPLS) Label Switched Paths (LSPs).  This document
 describes extensions to LSP ping so that LSP ping can be used for
 on-demand monitoring of MPLS Transport Profile (MPLS-TP) LSPs and
 pseudowires.  It also clarifies the procedures to be used for
 processing the related OAM packets.  This document describes how LSP
 ping can be used for on-demand connectivity verification (Section 3)
 and route tracing (Section 4) functions required in [RFC5860] and
 specified in [RFC6371].

1.1. Conventions Used in This Document

 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
 [RFC2119].
 There is considerable opportunity for confusion in use of the terms
 "on-demand connectivity verification" (CV), "on-demand route tracing"
 and "LSP ping."  In this document, we try to use the terms
 consistently as follows:
 o  LSP ping: refers to the mechanism - particularly as defined and
    used in referenced material;

Gray, et al. Standards Track [Page 3] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

 o  On-demand CV: refers to on-demand connectivity verification and --
    where both apply equally -- on-demand route tracing, as
    implemented using the LSP ping mechanism extended for support of
    MPLS-TP;
 o  On-demand route tracing: used in those cases where the LSP ping
    mechanism (as extended) is used exclusively for route tracing.
 From the perspective of on-demand CV and route tracing, we use the
 concepts of "Requester" and "Responder" as follows:
 o  Requester: Originator of an OAM Request message,
 o  Responder: Entity responding to an OAM Request message.
 Since, in this document, all messages are assumed to be carried in an
 LSP, all Request messages would be injected at the ingress to an LSP.
 A Responder might or might not be at the egress of this same LSP,
 given that it could receive Request messages as a result of time-to-
 live (TTL) expiry.  If a Reply is to be delivered via a reverse-path
 LSP, the message would again be inserted at the ingress of that LSP.

1.2. On-Demand CV for MPLS-TP LSPs Using IP Encapsulation

 LSP ping requires IP addressing on responding Label Switching Routers
 (LSRs) for performing OAM on MPLS-signaled LSPs and pseudowires.  In
 particular, in these cases, LSP ping packets generated by a Requester
 are encapsulated in an IP/UDP header with the destination address
 from the 127/8 range and then encapsulated in the MPLS label stack
 ([RFC4379] , [RFC5884]).  A Responder uses the presence of the 127/8
 destination address to identify OAM packets and relies further on the
 UDP port number to determine whether the packet is an LSP ping
 packet.  It is to be noted that this determination does not require
 IP forwarding capabilities.  It requires the presence of an IP host
 stack, which enables responding LSRs to process packets with a
 destination address from the 127/8 range.  [RFC1122] allocates the
 127/8 range as "Internal host loopback address" and [RFC1812] states
 that "a router SHOULD NOT forward, except over a loopback interface,
 any packet that has a destination address on network 127".

1.3. On-Demand CV for MPLS-TP LSPs Using Non-IP Encapsulation

 In certain MPLS-TP deployment scenarios, IP addressing might not be
 available or use some form of non-IP encapsulation might be preferred
 for on-demand CV, route tracing, and BFD packets.  In such scenarios,
 on-demand CV and/or route tracing SHOULD be run without IP
 addressing, using the Associated Channel (ACH) channel type specified
 in Section 3.

Gray, et al. Standards Track [Page 4] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

 Section 3.3 and Section 4.2 describe the theory of operation for
 performing on-demand CV over MPLS-TP LSPs with any non-IP
 encapsulation.

2. LSP Ping Extensions

2.1. New Address Type for Downstream Mapping TLV

 [RFC4379] defines the Downstream Mapping (DSMAP) TLV.  [RFC6424]
 further defines the Downstream Detailed Mapping (DDMAP) TLV.  This
 document defines the following new address type, which MAY be used in
 any DSMAP or DDMAP TLV included in an on-demand CV message:
             Type #        Address Type           K Octets
             ------        --------------         --------
                 5         Non IP                       12
             Figure 1: New Downstream Mapping Address Type
 The new address type indicates that no address is present in the
 DSMAP or DDMAP TLV.  However, IF_Num information (see definition of
 "IF_Num" in [RFC6370]) for both ingress and egress interfaces, as
 well as Multipath Information, is included in the format and MAY be
 present.
 IF_Num values of zero indicate that no IF_Num applies in the field in
 which this value appears.
 The Multipath Type SHOULD be set to zero (no multipath) when using
 this address type.
 When this address type is used, on receipt of an LSP ping echo
 request, interface verification MUST be bypassed.  Thus, the
 receiving node SHOULD only perform MPLS label control-plane/
 data-plane consistency checks.  Note that these consistency checks
 include checking the included identifier information.
 The new address type is also applicable to the Detailed Downstream
 Mapping (DDMAP) TLV defined in [RFC6424].

2.1.1. DSMAP/DDMAP Non-IP Address Information

 If the DSMAP (or DDMAP) TLV is included when sending on-demand CV
 packets using ACH, without IP encapsulation, the following
 information MUST be included in any DSMAP or DDMAP TLV that is
 included in the packet.  This information forms the address portion
 of the DSMAP TLV (as defined in [RFC4379]) or DDMAP TLV (as defined
 in [RFC6424] using one of the address information fields defined in

Gray, et al. Standards Track [Page 5] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

 [RFC4379] and extended to include non-IP identifier types in this
 document).
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               MTU             | Address Type  |    DS Flags   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               Ingress IF_Num (4 octets)                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                Egress IF_Num (4 octets)                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Multipath Type| Depth Limit   |        Multipath Length       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 2: New DSMAP/DDMAP Address Format
 Address Type will be 5 (as shown in Section 2.1 above).
 Ingress IF_Num identifies the ingress interface on the target node.
 A value of zero indicates that the interface is not part of the
 identifier.
 Egress IF_Num identifies the egress interface on the target node.  A
 value of zero indicates that the interface is not part of the
 identifier.
 The Multipath Type SHOULD be set to zero (no multipath) when using
 this address type.
 Including this TLV, with one or the other IF_Num (but not both) set
 to a non-zero value, in a request message that also includes a
 Destination Identifier TLV (as described in Section 2.2), is
 sufficient to identify the "per-interface" MIP in Section 7.3 of
 [RFC6370].
 Inclusion of this TLV with both IF_Num fields set to zero would be
 interpreted as specifying neither an ingress, nor an egress,
 interface.  Note that this is the same as not including the TLV;
 hence, including this TLV with both IF_Num values set to zero is NOT
 RECOMMENDED.
 Including this TLV with both IF_NUM fields set to a non-zero value
 will result in the responder sending a Return Code of 5 ("Downstream
 Mapping Mis-match") if either IF_Num is incorrect for this LSP or PW.

Gray, et al. Standards Track [Page 6] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

2.2. Source/Destination Identifier TLV

2.2.1. Source/Destination Identifier TLV Format

 The format for the identifier TLV is the same for both Source and
 Destination Identifier TLVs (only the type is different).  The format
 is as specified in the figure 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             Type              | Length = 8                    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Global_ID   (4 Octets)                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                   Node_ID   (4 Octets)                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          Figure 3: New Source/Destination Identifier Format
 Type will be one of either 13 or 14, depending on whether the TLV in
 question is a Source or Destination Identifier TLV.
 Global_ID is as defined in [RFC6370].
 Node_ID is as defined in [RFC6370].

2.2.2. Source Identifier TLV

 When sending on-demand CV packets using ACH, without IP
 encapsulation, there MAY be a need to identify the source of the
 packet.  This source identifier (Source ID) will be specified via the
 Source Identifier TLV, using the Identifier TLV defined in
 Section 2.2.1, containing the information specified above.
 An on-demand CV packet MUST NOT include more than one Source
 Identifier TLV.  The Source Identifier TLV MUST specify the
 identifier of the originator of the packet.  If more than one such
 TLV is present in an on-demand CV request packet, then error 1
 (Malformed echo request received; see Section 3.1 of [RFC4379]) MUST
 be returned, if it is possible to unambiguously identify the source
 of the packet.

Gray, et al. Standards Track [Page 7] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

2.2.3. Destination Identifier TLV

 When sending on-demand CV packets using ACH, without IP
 encapsulation, there MAY be a need to identify the destination of the
 packet.  This destination identifier (Destination ID) will be
 specified via the Destination Identifier TLV, using the Identifier
 TLV defined in Section 2.2.1, containing the information specified
 above.
 An on-demand CV packet MUST NOT include more than one Destination
 Identifier TLV.  The Destination Identifier TLV MUST specify the
 destination node for the packet.  If more than 1 such TLV is present
 in an on-demand CV Request packet, then error 1 (Malformed echo
 request received; see Section 3.1 of [RFC4379]) MUST be returned, if
 it is possible to unambiguously identify the source of the packet.

2.3. Identifying Statically Provisioned LSPs and PWs

 [RFC4379] specifies how an MPLS LSP under test is identified in an
 echo request.  A Target FEC Stack TLV is used to identify the LSP.
 In order to identify a statically provisioned LSP and PW, new target
 FEC Stack sub-TLVs are being defined.  The new sub-TLVs are assigned
 sub-type identifiers as follows and are described in the following
 sections.
       Type #   Sub-Type #       Length        Value Field
       ------   ----------       ------        -----------
         1         22              24          Static LSP
         1         23              32          Static Pseudowire
                  Figure 4: New Target FEC Sub-Types

Gray, et al. Standards Track [Page 8] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

2.3.1. Static LSP Sub-TLV

 The format of the Static LSP sub-TLV value field is specified in the
 following figure.  The value fields are taken from the definitions in
 [RFC6370].
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Source Global ID                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Source Node ID                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Source Tunnel Number      |        LSP Number             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    Destination Global ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Destination Node ID                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Destination Tunnel Number   |        Must be Zero           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 5: Static LSP FEC Sub-TLV
 The Source Global ID and Destination Global ID MAY be set to zero.
 When set to zero, the field is not applicable.

Gray, et al. Standards Track [Page 9] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

2.3.2. Static Pseudowire Sub-TLV

 The format of the Static PW sub-TLV value field is specified in the
 following figure.
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 +                      Service Identifier                       +
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Source Global ID                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Source Node ID                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Source AC-ID                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    Destination Global ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Destination Node ID                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Destination AC-ID                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    Figure 6: Static PW FEC Sub-TLV
 The Service Identifier is a 64-bit unsigned integer that is included
 in the first two words, as shown.  The Service Identifier identifies
 the service associated with the transport path under test.  The value
 MAY, for example, be an Attachment Group Identifier (AGI), type 0x01,
 as defined in [RFC4446].
 The Source Global ID and Destination Global ID MAY be set to zero.
 When either of these fields is set to zero, the corresponding Global
 ID is not applicable.  This might be done in a scenario where local
 scope is sufficient for uniquely identifying services.
 The Global ID and Node ID fields are defined in [RFC6370].  The AC-ID
 fields are defined in [RFC5003].

3. Performing On-Demand CV over MPLS-TP LSPs

 This section specifies how on-demand CV can be used in the context of
 MPLS-TP LSPs.  The on-demand CV function meets the on-demand
 connectivity verification requirements specified in [RFC5860],
 Section 2.2.3.  This function SHOULD NOT be performed except in the
 on-demand mode.  This function SHOULD be performed between

Gray, et al. Standards Track [Page 10] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

 Maintenance Entity Group End Points (MEPs) and Maintenance Entity
 Group Intermediate Points (MIPs) of PWs and LSPs, and between End
 Points of PWs, LSPs, and Sections.  In order for the on-demand CV
 packet to be processed at the desired MIP, the TTL of the MPLS label
 MUST be set such that it expires at the MIP to be probed.
 [RFC5586] defines an ACH mechanism for MPLS LSPs.  The mechanism is a
 generalization of the Associated Channel mechanism that [RFC4385]
 defined for use with pseudowires.  As a result, it is possible to use
 a single Associated Channel Type for either an LSP or pseudowire.
 A new Pseudowire Associated Channel Type (0x0025) is defined for use
 in performing on-demand connectivity verification.  Its use is
 described in the following sections.
 ACH TLVs SHALL NOT be associated with this channel type.
 Except as specifically stated in the sections below, message and TLV
 construction procedures for on-demand CV messages are as defined in
 [RFC4379].

3.1. LSP Ping with IP Encapsulation

 LSP ping packets, as specified in [RFC4379], are sent over the MPLS
 LSP for which OAM is being performed and contain an IP/UDP packet
 within them.  The IP header is not used for forwarding (since LSP
 forwarding is done using MPLS).  The IP header is used mainly for
 addressing and can be used in the context of MPLS-TP LSPs.  This form
 of on-demand CV OAM MUST be supported for MPLS-TP LSPs when IP
 addressing is in use.
 The on-demand CV echo response message MUST be sent on the reverse
 path of the LSP.  The reply MUST contain IP/UDP headers followed by
 the on-demand CV payload.  The destination address in the IP header
 MUST be set to that of the sender of the echo request message.  The
 source address in the IP header MUST be set to a valid address of the
 replying node.

3.2. On-Demand CV with IP Encapsulation, over ACH

 IP encapsulated on-demand CV packets MAY be sent over the MPLS LSP
 using the control channel (ACH).  The IP ACH type specified in
 [RFC4385] MUST be used in such a case.  The IP header is used mainly
 for addressing and can be used in the context of MPLS-TP LSPs.
 Note that the application-level control channel in this case is the
 reverse path of the LSP (or Pseudowire) using ACH.

Gray, et al. Standards Track [Page 11] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

 The on-demand CV echo response message MUST be sent on the reverse
 path of the LSP.  The response in this case SHOULD use ACH and SHOULD
 be IP encapsulated.
 If IP encapsulated, the destination address in the IP header MUST be
 set to that of the sender of the echo request message, and the source
 address in the IP header MUST be set to a valid address of the
 replying node.

3.3. Non-IP-Based On-Demand CV, Using ACH

 The OAM procedures defined in [RFC4379] require the use of IP
 addressing, and in some cases IP routing, to perform OAM functions.
 When the ACH header is used, IP addressing and routing is not needed.
 This section describes procedures for performing on-demand CV without
 a dependency on IP addressing and routing.
 In the non-IP case, when using on-demand CV via LSP ping with the ACH
 header, the on-demand CV request payload MUST directly follow the ACH
 header, and the LSP ping Reply mode [RFC4379] in the LSP ping echo
 request SHOULD be set to 4 (Reply via application level control
 channel).
 Note that the application-level control channel in this case is the
 reverse path of the LSP (or pseudowire) using ACH.
 The requesting node MAY attach a Source Identifier TLV (Section 2.2)
 to identify the node originating the request.
 If the Reply mode indicated in an on-demand CV Request is 4 (Reply
 via application level control channel), the on-demand CV reply
 message MUST be sent on the reverse path of the LSP using ACH.  The
 on-demand CV payload MUST directly follow the ACH header, and IP
 and/or UDP headers MUST NOT be attached.  The responding node MAY
 attach a Source Identifier TLV to identify the node sending the
 response.
 If a node receives an MPLS echo request packet over ACH, without IP/
 UDP headers, with a reply mode of 4, and if that node does not have a
 return MPLS LSP path to the echo request source, then the node SHOULD
 drop the echo request packet and not attempt to send a response.
 If a node receives an MPLS echo request with a reply mode other than
 4 (Reply via application level control channel), and if the node
 supports that reply mode, then it MAY respond using that reply mode.
 If the node does not support the reply mode requested, or is unable
 to reply using the requested reply mode in any specific instance, the

Gray, et al. Standards Track [Page 12] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

 node MUST drop the echo request packet and not attempt to send a
 response.

3.4. Reverse-Path Connectivity Verification

3.4.1. Requesting Reverse-Path Connectivity Verification

 A new Global flag, Validate Reverse Path (R), is being defined in the
 LSP ping packet header.  When this flag is set in the echo request,
 the Responder SHOULD return reverse-path FEC information, as
 described in Section 3.4.2.
 The R flag MUST NOT be set in the echo response.
 The Global Flags field is now a bit vector with the following format:
                     0                   1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    |             MBZ         |R|T|V|
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     Figure 7: Global Flags Field
 The V flag is defined in [RFC4379].  The T flag is defined in
 [RFC6425].  The R flag is defined in this document.
 The Validate FEC Stack (V) flag MAY be set in the echo response when
 reverse-path connectivity verification is being performed.

3.4.2. Responder Procedures

 When the R flag is set in the echo request, the responding node
 SHOULD attach a Reverse-path Target FEC Stack TLV in the echo
 response.  The requesting node (on receipt of the response) can use
 the Reverse-path Target FEC Stack TLV to perform reverse-path
 connectivity verification.  For co-routed bidirectional LSPs, the
 Reverse-path Target FEC Stack used for the on-demand CV will be the
 same in both the forward and reverse path of the LSP.  For associated
 bidirectional LSPs, the Target FEC Stack MAY be different for the
 reverse path.
 The format of the Reverse-path Target FEC Stack TLV is the same as
 that of the Target FEC Stack TLV defined in [RFC4379].  The rules for
 creating a Target FEC Stack TLV also apply to the Reverse-path Target
 FEC Stack TLV.

Gray, et al. Standards Track [Page 13] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

           Type         Meaning
           --------     ------------------------------------
              16        Reverse-path Target FEC Stack
           Figure 8: Reverse-Path Target FEC Stack TLV Type

3.4.3. Requester Procedures

 On receipt of the echo response, the requesting node MUST perform the
 following checks:
 1.  Perform interface and label-stack validation to ensure that the
     packet is received on the reverse path of the bidirectional LSP.
 2.  If the Reverse-path Target FEC Stack TLV is present in the echo
     response, then perform FEC validation.
 The verification in this case is performed as described for the
 Target FEC Stack in Section 3.6 of [RFC4379].
 If any of the validations fail, then the requesting node MUST drop
 the echo response and SHOULD log and/or report an error.

3.5. P2MP Considerations

 [RFC6425] describes how LSP ping can be used for OAM on P2MP LSPs
 with IP encapsulation.  This MUST be supported for MPLS-TP P2MP LSPs
 when IP addressing is used.  When IP addressing is not used, then the
 procedures described in Section 3.3 can be applied to P2MP MPLS-TP
 LSPs as well.

3.6. Management Considerations for Operation with Static MPLS-TP

 Support for on-demand CV on a static MPLS-TP LSP or pseudowire MAY
 require manageable objects to allow, for instance, configuring
 operating parameters such as identifiers associated with the
 statically configured LSP or PW.
 The specifics of this manageability requirement are out-of-scope in
 this document and SHOULD be addressed in appropriate management
 specifications.

3.7. Generic Associated Channel Label (GAL) Processing

 At the Requester, when encapsulating the LSP echo request (LSP ping)
 packet (with the IP ACH, or the Non IP ACH, codepoint), a GAL MUST be
 added before adding the MPLS LSP label, and sending the LSP Ping echo
 request packet in-band in the MPLS LSP.

Gray, et al. Standards Track [Page 14] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

 The GAL MUST NOT be considered as part of the MPLS label stack that
 requires verification by the Responder.  For this reason, a Nil FEC
 TLV MUST NOT be added or associated with the GAL.
 The GAL MUST NOT be included in DSMAP or DDMAP TLVs.
 Interface and Label Stack TLVs MUST include the whole label stack
 including the GAL.

4. Performing On-Demand Route Tracing over MPLS-TP LSPs

 This section specifies how on-demand CV route tracing can be used in
 the context of MPLS-TP LSPs.  The on-demand CV route tracing function
 meets the route tracing requirement specified in [RFC5860], Section
 2.2.3.
 This function SHOULD be performed on-demand.  This function SHOULD be
 performed between End Points and Intermediate Points of PWs and LSPs,
 and between End Points of PWs, LSPs and Sections.
 When performing on-demand CV route tracing, the requesting node
 inserts a Downstream Mapping TLV to get the downstream node
 information and to enable LSP verification along the transit nodes.
 The Downstream Mapping TLV can be used as is for performing route
 tracing.  If IP addressing is not in use, then the Address Type field
 in the Downstream Mapping TLV can be set to "Non IP" (Section 2.1).
 The Downstream Mapping TLV address type field can be extended to
 include other address types as needed.

4.1. On-Demand LSP Route Tracing with IP Encapsulation

 The mechanics of on-demand CV route tracing are similar to those
 described for ping in Section 3.1.  On-demand route tracing packets
 sent by the Requester MUST follow procedures described in [RFC4379].
 This form of on-demand CV OAM MUST be supported for MPLS-TP LSPs,
 when IP addressing is used.

4.2. Non-IP-Based On-Demand LSP Route Tracing, Using ACH

 This section describes procedures for performing LSP route tracing
 when using LSP ping with the ACH header and without any dependency on
 IP addressing.  The procedures specified in Section 3.3 with regards
 to the Source Identifier TLV apply to LSP route tracing as well.

Gray, et al. Standards Track [Page 15] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

4.2.1. Requester Procedure for Sending Echo Request Packets

 On-demand route tracing packets sent by the Requester MUST adhere to
 the format described in Section 3.3.  MPLS-TTL expiry (as described
 in [RFC4379]) will be used to direct the packets to specific nodes
 along the LSP path.

4.2.2. Requester Procedure for Receiving Echo Response Packets

 The on-demand CV route tracing responses will be received on the LSP
 itself, and the presence of an ACH header with channel type of on-
 demand CV is an indicator that the packet contains an on-demand CV
 payload.

4.2.3. Responder Procedure

 When an echo request reaches the Responder, the presence of the ACH
 channel type of on-demand CV will indicate that the packet contains
 on-demand CV data.  The on-demand CV data, the label stack, and the
 destination identifier are sufficient to identify the LSP associated
 with the echo request packet.  If there is an error and the node is
 unable to identify the LSP on which the echo response would be sent,
 the node MUST drop the echo request packet and not send any response
 back.  All responses MUST always be sent on an LSP path using the ACH
 header and ACH channel type of on-demand CV.

4.3. P2MP Considerations

 [RFC6425] describes how LSP ping can be used for OAM on P2MP LSPs.
 This MUST be supported for MPLS-TP P2MP LSPs when IP addressing is
 used.  When IP addressing is not used, then the procedures described
 in Section 4.2 can be applied to P2MP MPLS-TP LSPs as well.

4.4. ECMP Considerations

 On-demand CV using ACH SHOULD NOT be used when there is ECMP (Equal
 Cost Multi-Path) for a given LSP.  The inclusion of the additional
 ACH header can modify the hashing behavior for OAM packets that could
 result in incorrect monitoring of the path taken by data traffic.

5. Applicability

 The procedures specified in this document for non-IP encapsulation
 apply to MPLS-TP transport paths.  This includes LSPs and PWs when IP
 encapsulation is not desired.  However, when IP addressing is used,
 as in non MPLS-TP LSPs, procedures specified in [RFC4379] MUST be
 used.

Gray, et al. Standards Track [Page 16] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

6. Security Considerations

 This document does not itself introduce any new security
 considerations.  Those discussed in [RFC4379] are applicable to this
 document.
 Unlike typical deployment scenarios identified in [RFC4379], however,
 likely deployments of on-demand CV for transport paths involves a
 strong possibility that the techniques in this document may be used
 across MPLS administrative boundaries.  Where this may occur, it is
 RECOMMENDED that on-demand OAM is configured as necessary to ensure
 that Source Identifier TLVs are included in on-demand CV messages.
 This will allow implementations to filter OAM messages arriving from
 an unexpected or unknown source.

7. IANA Considerations

7.1. New Source and Destination Identifier TLVs

 IANA has assigned the following TLV types from the "Multi-Protocol
 Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
 registry, "TLVs and sub-TLVs" sub-registry (from the "Standards
 Action" TLV type range):
                                 Length
     Type #   TLV Name           Octets   Reference
     ------   -----------------  ------   ---------------------------
         13   Source ID            8      this document (Section 2.2)
         14   Destination ID       8      this document (Section 2.2)
       Figure 9: New Source and Destination Identifier TLV Types

7.2. New Target FEC Stack Sub-TLVs

 Section 2.3 defines 2 new sub-TLV types for inclusion within the LSP
 ping [RFC4379] Target FEC Stack TLV (1).
 IANA has assigned sub-type values to the following sub-TLVs from the
 "Multi-Protocol Label Switching Architecture (MPLS) Label Switched
 Paths (LSPs) Ping Parameters" registry, "TLVs and sub-TLVs" sub-
 registry.
 Value    Meaning                 Reference
 -----    -------------------     -----------------------------
 22       Static LSP              this document (Section 2.4.1)
 23       Static Pseudowire       this document (Section 2.4.2)

Gray, et al. Standards Track [Page 17] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

7.3. New Reverse-Path Target FEC Stack TLV

 Section 3.4.2 defines a new TLV type for inclusion in the LSP ping
 packet.
 IANA has assigned a type value to the TLV from the "Multi-Protocol
 Label Switching Architecture (MPLS) Label Switched Paths (LSPs) Ping
 Parameters" registry, "TLVs and sub-TLVs" sub-registry.
 Type     Meaning                        Reference
 -----    --------------------------     ---------------------------
    16    Reverse-path Target FEC        this document (Section 3.4)
          Stack TLV
 The sub-TLV space and assignments for this TLV will be the same as
 that for the Target FEC Stack TLV.  Sub-types for the Target FEC
 Stack TLV and the Reverse-path Target FEC Stack TLV MUST be kept the
 same.  Any new sub-type added to the Target FEC Stack TLV MUST apply
 to the Reverse-path Target FEC Stack TLV as well.

7.4. New Pseudowire Associated Channel Type

 On-demand connectivity verification requires a unique Associated
 Channel Type.  IANA has assigned a PW ACH Type from the "Pseudowire
 Associated Channel Types" registry as described below:
   Value     Description     TLV Follows  Reference
   ------    -------------   -----------  -------------------------
   0x0025    On-Demand CV         No      this document (Section 3)
 ACH TLVs SHALL NOT be associated with this channel type.

7.5. New Downstream Mapping Address Type Registry

 [RFC4379] defined several registries.  It also defined some value
 assignments without explicitly asking for IANA to create a registry
 to support additional value assignments.  One such case is in
 defining address types associated with the Downstream Mapping (DSMAP)
 TLV.
 This document extends RFC 4379 by defining a new address type for use
 with the Downstream Mapping and Downstream Detailed Mapping TLVs.
 Recognizing that the absence of a registry makes it possible to have
 collisions of "address-type" usages, IANA has established a new
 registry -- associated with both [RFC4379] and this document -- that
 initially allocates the following assignments:

Gray, et al. Standards Track [Page 18] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

 Type #     Address Type      K Octets    Reference
 ------     ------------      --------    --------------------------
      1     IPv4 Numbered           16    RFC 4379
      2     IPv4 Unnumbered         16    RFC 4379
      3     IPv6 Numbered           40    RFC 4379
      4     IPv6 Unnumbered         28    RFC 4379
      5     Non IP                  12    this document (Sect. 2.1.1)
               Downstream Mapping Address Type Registry
 Because the field in this case is an 8-bit field, the allocation
 policy for this registry is "Standards Action."

8. Contributing Authors and Acknowledgements

 The following individuals contributed materially to this document:
 o  Thomas D. Nadeau, CA Technologies
 o  Nurit Sprecher, Nokia Siemens Networks
 o  Yaacov Weingarten, Nokia Siemens Networks
 In addition, we would like to thank the following individuals for
 their efforts in reviewing and commenting on the document:
 o  Adrian Farrel
 o  Alexander Vaishtein
 o  David Sinicrope (Routing Directorate)
 o  Greg Mirsky
 o  Hideki Endo
 o  Huub van Helvoort
 o  Joel Halpern (Routing Directorate)
 o  Loa Andersson
 o  Mach Chen
 o  Mahesh Akula
 o  Sam Aldrin

Gray, et al. Standards Track [Page 19] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

 o  Sandra Murphy (Security Directorate)
 o  Yaacov Weingarten
 o  Yoshinori Koike
 o  Zhenlong Cui

9. References

9.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol
            Label Switched (MPLS) Data Plane Failures", RFC 4379,
            February 2006.
 [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, February 2006.
 [RFC5586]  Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
            Associated Channel", RFC 5586, June 2009.
 [RFC6370]  Bocci, M., Swallow, G., and E. Gray, "MPLS Transport
            Profile (MPLS-TP) Identifiers", RFC 6370, September 2011.
 [RFC6424]  Bahadur, N., Kompella, K., and G. Swallow, "Mechanism for
            Performing Label Switched Path Ping (LSP Ping) over MPLS
            Tunnels", RFC 6424, November 2011.
 [RFC6425]  Saxena, S., Swallow, G., Ali, Z., Farrel, A., Yasukawa,
            S., and T. Nadeau, "Detecting Data-Plane Failures in
            Point-to-Multipoint MPLS - Extensions to LSP Ping",
            RFC 6425, November 2011.

9.2. Informative References

 [RFC1122]  Braden, R., "Requirements for Internet Hosts -
            Communication Layers", STD 3, RFC 1122, October 1989.
 [RFC1812]  Baker, F., "Requirements for IP Version 4 Routers",
            RFC 1812, June 1995.
 [RFC4446]  Martini, L., "IANA Allocations for Pseudowire Edge to Edge
            Emulation (PWE3)", BCP 116, RFC 4446, April 2006.

Gray, et al. Standards Track [Page 20] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

 [RFC5003]  Metz, C., Martini, L., Balus, F., and J. Sugimoto,
            "Attachment Individual Identifier (AII) Types for
            Aggregation", RFC 5003, September 2007.
 [RFC5860]  Vigoureux, M., Ward, D., and M. Betts, "Requirements for
            Operations, Administration, and Maintenance (OAM) in MPLS
            Transport Networks", RFC 5860, May 2010.
 [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
            "Bidirectional Forwarding Detection (BFD) for MPLS Label
            Switched Paths (LSPs)", RFC 5884, June 2010.
 [RFC6371]  Busi, I. and D. Allan, "Operations, Administration, and
            Maintenance Framework for MPLS-Based Transport Networks",
            RFC 6371, September 2011.

Gray, et al. Standards Track [Page 21] RFC 6426 MPLS On-Demand Connectivity Verification November 2011

Authors' Addresses

 Eric Gray
 Ericsson
 900 Chelmsford Street
 Lowell, MA  01851
 US
 Phone: +1 978 275 7470
 EMail: eric.gray@ericsson.com
 Nitin Bahadur
 Juniper Networks, Inc.
 1194 N. Mathilda Avenue
 Sunnyvale, CA  94089
 US
 Phone: +1 408 745 2000
 EMail: nitinb@juniper.net
 URI:   www.juniper.net
 Sami Boutros
 Cisco Systems, Inc.
 3750 Cisco Way
 San Jose, CA  95134
 US
 EMail: sboutros@cisco.com
 Rahul Aggarwal
 EMail: raggarwa_1@yahoo.com

Gray, et al. Standards Track [Page 22]

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