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Versions: (draft-yasukawa-mpls-p2mp-lsp-ping) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 RFC 6425

Network Working Group                                 A. Farrel (Editor)
Internet-Draft                                        Old Dog Consulting
Intended Status: Standards Track                             S. Yasukawa
Updates: RFC4379                                                     NTT
Created: September 10, 2008
Expires: March 10, 2009


     Detecting Data Plane Failures in Point-to-Multipoint Multiprotocol
             Label Switching (MPLS) - Extensions to LSP Ping

                  draft-ietf-mpls-p2mp-lsp-ping-07.txt

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Abstract

   Recent proposals have extended the scope of Multiprotocol Label
   Switching (MPLS) Label Switched Paths (LSPs) to encompass
   point-to-multipoint (P2MP) LSPs.

   The requirement for a simple and efficient mechanism that can be
   used to detect data plane failures in point-to-point (P2P) MPLS LSPs
   has been recognized and has led to the development of techniques
   for fault detection and isolation commonly referred to as "LSP Ping".

   The scope of this document is fault detection and isolation for P2MP
   MPLS LSPs. This documents does not replace any of the mechanisms of
   LSP Ping, but clarifies their applicability to MPLS P2MP LSPs, and
   extends the techniques and mechanisms of LSP Ping to the MPLS P2MP
   environment.

Yasukawa and Farrel                                             [Page 1]

Internet Draft     draft-ietf-mpls-p2mp-lsp-ping-07.txt   September 2008

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 [RFC2119].

Contents

   1. Introduction ................................................... 4
   1.1 Design Considerations ......................................... 5
   2. Notes on Motivation ............................................ 6
   2.1. Basic Motivations for LSP Ping ............................... 6
   2.2. Motivations for LSP Ping for P2MP LSPs ....................... 8
   2.3 Bootstrapping Other OAM Procedures Using LSP Ping ............. 9
   3. Operation of LSP Ping for a P2MP LSP ........................... 9
   3.1. Identifying the LSP Under Test ............................... 9
   3.1.1. Identifying a P2MP MPLS TE LSP ............................. 9
   3.1.1.1. RSVP P2MP IPv4 Session Sub-TLV ........................... 9
   3.1.1.2. RSVP P2MP IPv6 Session Sub-TLV .......................... 10
   3.1.2. Identifying a Multicast LDP LSP ........................... 10
   3.1.2.1. Multicast LDP FEC Stack Sub-TLV ......................... 11
   3.2. Ping Mode Operation ......................................... 12
   3.2.1. Controlling Responses to LSP Pings ........................ 12
   3.2.2. Ping Mode Egress Procedures ............................... 12
   3.2.3. Jittered Responses ........................................ 13
   3.2.4. P2MP Responder Identifier TLV and Sub-TLVs ................ 14
   3.2.5. Echo Jitter TLV ........................................... 15
   3.2.6. Echo Response Reporting ................................... 15
   3.3. Traceroute Mode Operation ................................... 16
   3.3.1. Traceroute Responses at Non-Branch Nodes .................. 17
   3.3.1.1. Correlating Traceroute Responses ........................ 17
   3.3.2.  Traceroute Responses at Branch Nodes ..................... 18
   3.3.2.1. Node Properties TLV ..................................... 18
   3.3.2.2. Branching Properties Sub-TLV ............................ 19
   3.3.2.3. Egress Address Sub-TLV .................................. 20
   3.3.2.4. Correlating Traceroute Responses ........................ 21
   3.3.3. Traceroute Responses at Bud Nodes ......................... 21
   3.3.4. Non-Response to Traceroute Echo Requests .................. 22
   3.3.5. Additions to Downstream Mapping Multipath Information ..... 22
   3.3.6. Echo Response Reporting ................................... 24
   3.3.6.1. Reporting Multiple Conditions Using The DDM TLV ......... 24
   4. Operation of LSP Ping for Bootstrapping Other OAM Mechanisms .. 25
   5. Non-compliant Routers ......................................... 26
   6. OAM Considerations ............................................ 26
   7. IANA Considerations ........................................... 27
   7.1. New Sub-TLV Types ........................................... 27
   7.2. New Multipath Type .......................................... 27
   7.3. New TLVs .................................................... 28
   7.4. New Return Code ............................................. 28
   7.5. New Sub-TLV Value for the Downstream Detailed Mapping TLV ... 28

Yasukawa and Farrel                                             [Page 2]

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   8. Security Considerations ....................................... 29
   9. Acknowledgements .............................................. 29
   10. Intellectual Property Considerations ......................... 29
   11. Normative References ......................................... 30
   12. Informative References ....................................... 30
   13. Authors' Addresses ........................................... 31
   14. Full Copyright Statement ..................................... 32

0. Change Log

   This section to be removed before publication as an RFC.

0.1 Changes from 00 to 01

   - Update references.
   - Fix boilerplate.

0.2 Changes from 01 to 02

   - Update entire document so that it is not specific to MPLS-TE, but
     also includes multicast LDP LSPs.
   - Move the egress identifier sub-TLVs from the FEC Stack TLV to a new
     egress identifier TLV.
   - Include Multicast LDP FEC Stack sub-TLV definition from [MCAST-CV].
   - Add brief section on use of LSP Ping for bootstrapping.
   - Add new references to References section.
   - Add details of two new authors.

0.3 Changes from 02 to 03

   - Update references.
   - Update boilerplate.
   - Fix typos.
   - Clarify in 3.2.2 that a recipient of an echo request must reply
     only once it has applied incoming rate limiting.
   - Tidy references to bootstrapping for [MCAST-CV] in 1.1.
   - Allow multiple sub-TLVs in the P2MP Egress Identifier TLV in
     sections 3.2.1, 3.2.2, 3.2.4, 3.3.1, and 3.3.4.
   - Clarify how to handle a P2MP Egress Identifier TLV with no sub-TLVs
     in sections 3.2.1 and 3.2.2.

0.4 Changes from 03 to 04

   - Revert to previous text in sections 3.2.1, 3.2.2, 3.2.4, 3.3.1, and
     3.3.4 with respect to multiple sub-TLVs in the P2MP Egress
     Identifier TLV.





Yasukawa and Farrel                                             [Page 3]

Internet Draft     draft-ietf-mpls-p2mp-lsp-ping-07.txt   September 2008

0.5 Changes from 04 to 05

   - Change coordinates for Tom Nadeau. Section 13.
   - Fix typos.
   - Update references.
   - Resolve all acronym expansions.

0.6 Changes from 05 to 06

   - New section, 3.2.6, to explain echo response reporting in the Ping
     case.
   - New section, 3.3.7, to explain echo response reporting in the
     Traceroute case.
   - Sections 3.3.2, 3.3.5, and 5. Retire the E-flag for identification
     of bud nodes. Use the B-flag in a Downstream Mapping TLV with a
     zero address to provide the necessary indication.
   - Section 3.3.4. Note the use of ALLROUTERS address as per RFC 4379
   - Section 7. Suggest values for IANA assignment.
   - Rename "P2MP Responder Identifier TLV" to "P2MP Responder
     Identifier TLV", "Egress Identifier sub-TLV" to "Responder
     Identifier sub-TLV", and "P2MP egresses" multipath type to "P2MP
     responder". This allows any LSR on the P2MP LSP to be the target
     of, or responder to, an echo request.

0.7 Changes from 06 to 07

   - Sections 3.3.2 and 3.3.3. Delete section 3.3.5. New sections
     3.3.2.1 through 3.3.2.3: Retire B-flag from Downstream Mapping TLV.
     Introduce new Node Properties TLV with Branching Properties and
     Egress Address sub-TLVs.
   - Section 3.3.2.4: Clarify rules on presence of Multipath Information
     in Downstream Mapping TLVs.
   - Section 3.3.5: Clarify padding rules.
   - Section 3.3.6: Updated to use Downstream Detailed Mapping TLVs for
     multiple return conditions reported by a single echo response.
   - Section 7: Update IANA values and add new sub-sections.
   - Section 11: Add reference draft-ietf-mpls-lsp-ping-enhanced-dsmap.
   - Section 13: Update Bill Fenner's coordinates.

1. Introduction

   Simple and efficient mechanisms that can be used to detect data plane
   failures in point-to-point (P2P) Multiprotocol Label Switching (MPLS)
   Label Switched Paths (LSP) are described in [RFC4379]. The techniques
   involve information carried in an MPLS "echo request" and "echo
   reply", and mechanisms for transporting the echo reply. The echo
   request and reply messages provide sufficient information to check
   correct operation of the data plane, as well as a mechanism to verify
   the data plane against the control plane, and thereby localize
   faults. The use of reliable channels for echo reply messages as

Yasukawa and Farrel                                             [Page 4]

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   described in [RFC4379] enables more robust fault isolation. This
   collection of mechanisms is commonly referred to as "LSP Ping".

   The requirements for point-to-multipoint (P2MP) MPLS traffic
   engineered (TE) LSPs are stated in [RFC4461]. [RFC4875] specifies a
   signaling solution for establishing P2MP MPLS TE LSPs.

   The requirements for point-to-multipoint extensions to the Label
   Distribution Protocol (LDP) are stated in [P2MP-LDP-REQ]. [P2MP-LDP]
   specifies extensions to LDP for P2MP MPLS.

   P2MP MPLS LSPs are at least as vulnerable to data plane faults or to
   discrepancies between the control and data planes as their P2P
   counterparts. Mechanisms are, therefore, desirable to detect such
   data plane faults in P2MP MPLS LSPs as described in [RFC4687].

   This document extends the techniques described in [RFC4379] such
   that they may be applied to P2MP MPLS LSPs and so that they can be
   used to bootstrap other Operations and Management (OAM) procedures
   such as [MCAST-CV]. This document stresses the reuse of existing LSP
   Ping mechanisms used for P2P LSPs, and applies them to P2MP MPLS LSPs
   in order to simplify implementation and network operation.

1.1 Design Considerations

   An important consideration for designing LSP Ping for P2MP MPLS LSPs
   is that every attempt is made to use or extend existing mechanisms
   rather than invent new mechanisms.

   As for P2P LSPs, a critical requirement is that the echo request
   messages follow the same data path that normal MPLS packets traverse.
   However, it can be seen this notion needs to be extended for P2MP
   MPLS LSPs, as in this case an MPLS packet is replicated so that it
   arrives at each egress (or leaf) of the P2MP tree.

   MPLS echo requests are meant primarily to validate the data plane,
   and they can then be used to validate data plane state against the
   control plane. They may also be used to bootstrap other OAM
   procedures such as [MPLS-BFD] and [MCAST-CV]. As pointed out in
   [RFC4379], mechanisms to check the liveness, function, and
   consistency of the control plane are valuable, but such mechanisms
   are not a feature of LSP Ping and are not covered in this document.

   As is described in [RFC4379], to avoid potential Denial of Service
   attacks, it is RECOMMENDED to regulate the LSP Ping traffic passed to
   the control plane. A rate limiter should be applied to the well-known
   UDP port defined for use by LSP Ping traffic.




Yasukawa and Farrel                                             [Page 5]

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2. Notes on Motivation

2.1. Basic Motivations for LSP Ping

   The motivations listed in [RFC4379] are reproduced here for
   completeness.

   When an LSP fails to deliver user traffic, the failure cannot always
   be detected by the MPLS control plane. There is a need to provide a
   tool that enables users to detect such traffic "black holes" or
   misrouting within a reasonable period of time. A mechanism to isolate
   faults is also required.

   [RFC4379] describes a mechanism that accomplishes these goals. This
   mechanism is modeled after the ping/traceroute paradigm: ping (ICMP
   echo request [RFC792]) is used for connectivity checks, and
   traceroute is used for hop-by-hop fault localization as well as path
   tracing. [RFC4379] specifies a "ping mode" and a "traceroute" mode
   for testing MPLS LSPs.

   The basic idea as expressed in [RFC4379] is to test that the packets
   that belong to a particular Forwarding Equivalence Class (FEC)
   actually end their MPLS path on an LSR that is an egress for that
   FEC. [RFC4379] achieves this test by sending a packet (called an
   "MPLS echo request") along the same data path as other packets
   belonging to this FEC. An MPLS echo request also carries information
   about the FEC whose MPLS path is being verified. This echo request is
   forwarded just like any other packet belonging to that FEC. In "ping"
   mode (basic connectivity check), the packet should reach the end of
   the path, at which point it is sent to the control plane of the
   egress LSR, which then verifies that it is indeed an egress for the
   FEC. In "traceroute" mode (fault isolation), the packet is sent to
   the control plane of each transit LSR, which performs various checks
   that it is indeed a transit LSR for this path; this LSR also returns
   further information that helps to check the control plane against the
   data plane, i.e., that forwarding matches what the routing protocols
   determined as the path.

   One way these tools can be used is to periodically ping a FEC to
   ensure connectivity. If the ping fails, one can then initiate a
   traceroute to determine where the fault lies. One can also
   periodically traceroute FECs to verify that forwarding matches the
   control plane; however, this places a greater burden on transit LSRs
   and should be used with caution.

2.2. Motivations for LSP Ping for P2MP LSPs

   As stated in [RFC4687], MPLS has been extended to encompass P2MP
   LSPs. As with P2P MPLS LSPs, the requirement to detect, handle, and
   diagnose control and data plane defects is critical. For operators

Yasukawa and Farrel                                             [Page 6]

Internet Draft     draft-ietf-mpls-p2mp-lsp-ping-07.txt   September 2008

   deploying services based on P2MP MPLS LSPs, the detection and
   specification of how to handle those defects is important because
   such defects may affect the fundamentals of an MPLS network, but also
   because they may impact service level specification commitments for
   customers of their network.

   P2MP LDP [P2MP-LDP] uses the Label Distribution Protocol to establish
   multicast LSPs. These LSPs distribute data from a single source to
   one or more destinations across the network according to the next
   hops indicated by the routing protocols. Each LSP is identified by an
   MPLS multicast FEC.

   P2MP MPLS TE LSPs [RFC4875] may be viewed as MPLS tunnels with a
   single ingress and multiple egresses. The tunnels, built on P2MP
   LSPs, are explicitly routed through the network. There is no concept
   or applicability of a FEC in the context of a P2MP MPLS TE LSP.

   MPLS packets inserted at the ingress of a P2MP LSP are delivered
   equally (barring faults) to all egresses. In consequence, the basic
   idea of LSP Ping for P2MP MPLS TE LSPs may be expressed as an
   intention to test that packets that enter (at the ingress) a
   particular P2MP LSP actually end their MPLS path on the LSRs that are
   the (intended) egresses for that LSP. The idea may be extended to
   check selectively that such packets reach specific egresses.

   The technique in this document makes this test by sending an LSP Ping
   echo request message along the same data path as the MPLS packets. An
   echo request also carries the identification of the P2MP MPLS LSP
   (multicast LSP or P2MP TE LSP) that it is testing. The echo request
   is forwarded just as any other packet using that LSP, and so is
   replicated at branch points of the LSP and should be delivered to all
   egresses. In "ping" mode (basic connectivity check), the echo request
   should reach the end of the path, at which point it is sent to the
   control plane of the egress LSRs, which verify that they are indeed
   an egress (leaf) of the P2MP LSP. An echo response message is sent by
   an egress to the ingress to confirm the successful receipt (or
   announce the erroneous arrival) of the echo request.

   In "traceroute" mode (fault isolation), the echo request is sent to
   the control plane at each transit LSR, and the control plane checks
   that it is indeed a transit LSR for this P2MP MPLS LSP. The transit
   LSR also returns information on an echo response that helps verify
   the control plane against the data plane. That is, the information
   is used by the ingress to check that the data plane forwarding
   matches what is signaled by the control plane.

   P2MP MPLS LSPs may have many egresses, and it is not necessarily the
   intention of the initiator of the ping or traceroute operation to
   collect information about the connectivity or path to all egresses.
   Indeed, in the event of pinging all egresses of a large P2MP MPLS

Yasukawa and Farrel                                             [Page 7]

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   LSP, it might be expected that a large number of echo responses would
   arrive at the ingress independently but at approximately the same
   time. Under some circumstances this might cause congestion at or
   around the ingress LSR. Therefore, the procedures described in this
   document provide a mechanism that allows the responders to randomly
   delay (or jitter) their responses so that the chances of swamping the
   ingress are reduced.

   Further, the procedures in this document allow the initiator to limit
   the scope of an LSP Ping echo request (ping or traceroute mode) to
   one specific intended egress.

   The scalability issues surrounding LSP Ping for P2MP MPLS LSPs may be
   addressed by other mechanisms such as [MCAST-CV] that utilize the LSP
   Ping procedures in this document to provide bootstrapping mechanisms
   as described in Section 2.3.

   LSP Ping can be used to periodically ping a P2MP MPLS LSP to ensure
   connectivity to any or all of the egresses. If the ping fails,
   the operator or an automated process can then initiate a traceroute
   to determine where the fault is located within the network. A
   traceroute may also be used periodically to verify that data plane
   forwarding matches the control plane state; however, this places an
   increased burden on transit LSRs and should be used infrequently and
   with caution.

2.3 Bootstrapping Other OAM Procedures Using LSP Ping

   [MPLS-BFD] describes a process where LSP Ping [RFC4379] is used to
   bootstrap the Bidirectional Forwarding Detection (BFD) mechanism
   [BFD] for use to track the liveliness of an MPLS LSP. In particular
   BFD can be used to detect a data plane failure in the forwarding
   path of an MPLS LSP.

   Requirements for MPLS P2MP LSPs extend to hundreds or even thousands
   of endpoints. If a protocol required explicit acknowledgments to
   each probe for connectivity verification, the response load at the
   root would be overwhelming.

   A more scalable approach to monitoring P2MP LSP connectivity is
   described in [MCAST-CV]. It relies on using the MPLS echo request and
   echo response messages of LSP Ping [RFC4379] to bootstrap the
   monitoring mechanism in a manner similar to [MPLS-BFD]. The actual
   monitoring is done using a separate process defined in [MCAST-CV].

   Note that while the approach described in [MCAST-CV] was developed in
   response to the multicast scalability problem, it can be applied to
   P2P LSPs as well.



Yasukawa and Farrel                                             [Page 8]

Internet Draft     draft-ietf-mpls-p2mp-lsp-ping-07.txt   September 2008

3. Operation of LSP Ping for a P2MP LSP

   This section describes how LSP Ping is applied to P2MP MPLS LSPs.
   It covers the mechanisms and protocol fields applicable to both ping
   mode and traceroute mode. It explains the responsibilities of the
   initiator (ingress), transit nodes, and receivers (egresses).

3.1. Identifying the LSP Under Test

3.1.1. Identifying a P2MP MPLS TE LSP

   [RFC4379] defines how an MPLS TE LSP under test may be identified in
   an echo request. A Target FEC Stack TLV is used to carry either an
   RSVP IPv4 Session or an RSVP IPv6 Session sub-TLV.

   In order to identify the P2MP MPLS TE LSP under test, the echo
   request message MUST carry a Target FEC Stack TLV, and this MUST
   carry exactly one of two new sub-TLVs: either an RSVP P2MP IPv4
   Session sub-TLV or an RSVP P2MP IPv6 Session sub-TLV. These sub-TLVs
   carry fields from the RSVP-TE P2MP Session and Sender-Template
   objects [RFC4875] and so provide sufficient information to uniquely
   identify the LSP.

   The new sub-TLVs are assigned sub-type identifiers as follows, and
   are described in the following sections.

      Sub-Type #       Length              Value Field
      ----------       ------              -----------
             TBD         20                RSVP P2MP IPv4 Session
             TBD         56                RSVP P2MP IPv6 Session

3.1.1.1. RSVP P2MP IPv4 Session Sub-TLV

   The format of the RSVP P2MP IPv4 Session sub-TLV value field is
   specified in the following figure. The value fields are taken from
   the definitions of the P2MP IPv4 LSP Session Object and the P2MP
   IPv4 Sender-Template Object in [RFC4875]. Note that the Sub-Group
   ID of the Sender-Template is not required.













Yasukawa and Farrel                                             [Page 9]

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       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           P2MP ID                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Must Be Zero         |     Tunnel ID                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Extended Tunnel ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   IPv4 tunnel sender address                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Must Be Zero         |            LSP ID             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.1.1.2. RSVP P2MP IPv6 Session Sub-TLV

   The format of the RSVP P2MP IPv6 Session sub-TLV value field is
   specified in the following figure. The value fields are taken from
   the definitions of the P2MP IPv6 LSP Session Object, and the
   P2MP IPv6 Sender-Template Object in [RFC4875]. Note that the
   Sub-Group ID of the Sender-Template is not required.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                           P2MP ID                             |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Must Be Zero         |     Tunnel ID                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                       Extended Tunnel ID                      |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                   IPv6 tunnel sender address                  |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Must Be Zero         |            LSP ID             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.1.2. Identifying a Multicast LDP LSP

   [RFC4379] defines how a P2P LDP LSP under test may be identified in
   an echo request. A Target FEC Stack TLV is used to carry one or more
   sub-TLVs (for example, an IPv4 Prefix FEC sub-TLV) that identify the
   LSP.

   In order to identify a multicast LDP LSP under test, the echo request

Yasukawa and Farrel                                            [Page 10]

Internet Draft     draft-ietf-mpls-p2mp-lsp-ping-07.txt   September 2008

   message MUST carry a Target FEC Stack TLV, and this MUST carry
   exactly one new sub-TLV: the Multicast LDP FEC Stack sub-TLV. This
   sub-TLV uses fields from the multicast LDP messages [P2MP-LDP] and so
   provides sufficient information to uniquely identify the LSP.

   The new sub-TLV is assigned a sub-type identifier as follows, and
   is described in the following section.

      Sub-Type #       Length              Value Field
      ----------       ------              -----------
             TBD       Variable            Multicast LDP FEC Stack

3.1.2.1. Multicast LDP FEC Stack Sub-TLV

   The format of the Multicast LDP FEC Stack sub-TLV 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Address Family         | Address Length| Root LSR Addr |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                   Root LSR Address (Cont.)                    ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Opaque Length          |         Opaque Value ...      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   ~                                                               ~
   |                                                               |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Address Family

      A two octet quantity containing a value from ADDRESS FAMILY
      NUMBERS in [IANA-PORT] that encodes the address family for the
      Root LSR Address.

   Address Length

      The length of the Root LSR Address in octets.

   Root LSR Address

      An address of the LSR at the root of the P2MP LSP encoded
      according to the Address Family field.




Yasukawa and Farrel                                            [Page 11]

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   Opaque Length

       The length of the Opaque Value, in octets.

   Opaque Value

      An opaque value elements of which uniquely identifies the P2MP LSP
      in the context of the Root LSR.

   If the Address Family is IPv4, the Address Length MUST be 4. If the
   Address Family is IPv6, the Address Length MUST be 16. No other
   Address Family values are defined at present.

3.2. Ping Mode Operation

3.2.1. Controlling Responses to LSP Pings

   As described in Section 2.2, it may be desirable to restrict the
   operation of LSP Ping to a single egress. Since echo requests are
   forwarded through the data plane without interception by the control
   plane (compare with traceroute mode), there is no facility to limit
   the propagation of echo requests, and they will automatically be
   forwarded to all (reachable) egresses.

   However, the intended egress under test can be identified by the
   inclusion of a P2MP Responder Identifier TLV containing an IPv4 P2MP
   Responder Identifier sub-TLV or an IPv6 P2MP Responder Identifier
   sub-TLV. The P2MP Responder Identifier TLV SHOULD contain precisely
   one sub-TLV. If the TLV contains no sub-TLVs it SHOULD be processed
   as if the whole TLV were absent (causing all egresses to respond as
   described below). If the TLV contains more than one sub-TLV, the
   first MUST be processed as described in this document, and subsequent
   sub-TLVs SHOULD be ignored.

   An initiator may indicate that it wishes all egresses to respond to
   an echo request by omitting the P2MP Responder Identifier TLV.

   Note that the ingress of a multicast LDP LSP will not know the
   identities of the egresses of the LSP except by some external means
   such as running P2MP LSP Ping to all egresses.

3.2.2. Ping Mode Egress Procedures

   An egress node is RECOMMENDED to rate limit its receipt of echo
   request messages as described in [RFC4379]. After rate limiting, an
   egress node that receives an echo request carrying an RSVP P2MP IPv4
   Session sub-TLV, an RSVP P2MP IPv6 Session sub-TLV, or a Multicast
   LDP FEC Stack sub-TLV MUST determine whether it is an intended egress
   of the P2MP LSP in question by checking with the control plane. If it
   is not supposed to be an egress, it MUST respond according to the

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   setting of the Response Type field in the echo message following the
   rules defined in [RFC4379].

   If the egress node that receives an echo request and allows it
   through its rate limiting is an intended egress of the P2MP LSP, the
   node MUST check to see whether it is an intended Ping recipient. If a
   P2MP Responder Identifier TLV is present and contains an address that
   indicates any address that is local to the node, the node MUST
   respond according to the setting of the Response Type field in the
   echo message following the rules defined in [RFC4379]. If the P2MP
   Responder Identifier TLV is present, but does not identify the egress
   node, it MUST NOT respond to the echo request. If the P2MP Responder
   Identifier TLV is not present (or, in the error case, is present, but
   does not contain any sub-TLVs), but the egress node that received the
   echo request is an intended egress of the LSP, the node MUST respond
   according to the setting of the Response Type field in the echo
   message following the rules defined in [RFC4379].

3.2.3. Jittered Responses

   The initiator (ingress) of a ping request MAY request the responding
   egress to introduce a random delay (or jitter) before sending the
   response. The randomness of the delay allows the responses from
   multiple egresses to be spread over a time period. Thus this
   technique is particularly relevant when the entire LSP tree is being
   pinged since it helps prevent the ingress (or nearby routers) from
   being swamped by responses, or from discarding responses due to rate
   limits that have been applied.

   It is desirable for the ingress to be able to control the bounds
   within which the egress delays the response. If the tree size is
   small, only a small amount of jitter is required, but if the tree is
   large, greater jitter is needed. The ingress informs the egresses of
   the jitter bound by supplying a value in a new TLV (the Echo Jitter
   TLV) carried on the echo request message. If this TLV is present,
   the responding egress MUST delay sending a response for a random
   amount of time between zero seconds and the value indicated in the
   TLV. If the TLV is absent, the responding egress SHOULD NOT introduce
   any additional delay in responding to the echo request.

   LSP ping SHOULD NOT be used to attempt to measure the round-trip
   time for data delivery. This is because the LSPs are unidirectional,
   and the echo response is often sent back through the control plane.
   The timestamp fields in the echo request/response MAY be used to
   deduce some information about delivery times and particularly the
   variance in delivery times.

   The use of echo jittering does not change the processes for gaining
   information, but note that the responding egress MUST set the value
   in the Timestamp Received fields before applying any delay.

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   It is RECOMMENDED that echo response jittering is not used except in
   the case of P2MP LSPs. If the Echo Jitter TLV is present in an echo
   request for any other type of TLV, the responding egress MAY apply
   the jitter behavior described here.

3.2.4. P2MP Responder Identifier TLV and Sub-TLVs

   A new TLV is defined for inclusion in the Echo request message.

   The P2MP Responder Identifier TLV is assigned the TLV type value TBD
   and is encoded as follows.

       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=TBD(P2MP Responder ID TLV)|       Length = Variable       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                          Sub-TLVs                             ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Sub-TLVs:

        Zero, one or more sub-TLVs as defined below.

        If no sub-TLVs are present, the TLV MUST be processed as if it
        were absent. If more than one sub-TLV is present the first MUST
        be processed as described in this document, and subsequent
        sub-TLVs SHOULD be ignored.

   The P2MP Responder Identifier TLV only has meaning on an echo request
   message. If present on an echo response message, it SHOULD be
   ignored.

   Two sub-TLVs are defined for inclusion in the P2MP Responder
   Identifier TLV carried on the echo request message. These are:

      Sub-Type #       Length             Value Field
      ----------       ------             -----------
              1             4             IPv4 P2MP Responder Identifier
              2            16             IPv6 P2MP Responder Identifier

   The value of an IPv4 P2MP Responder Identifier consists of four
   octets of an IPv4 address. The IPv4 address is in network byte order.

   The value of an IPv6 P2MP Responder Identifier consists of sixteen
   octets of an IPv6 address. The IPv6 address is in network byte order.





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3.2.5. Echo Jitter TLV

   A new TLV is defined for inclusion in the Echo request message.

   The Echo Jitter TLV is assigned the TLV type value TBD and is encoded
   as follows.

       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 = TBD (Jitter TLV)  |          Length = 4           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Jitter time                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Jitter time:

        This field specifies the upper bound of the jitter period that
        should be applied by a responding node to determine how long to
        wait before sending an echo response. A responding node SHOULD
        wait a random amount of time between zero seconds and the value
        specified in this field.

        Jitter time is specified in milliseconds.

   The Echo Jitter TLV only has meaning on an echo request message. If
   present on an echo response message, it SHOULD be ignored.

3.2.6. Echo Response Reporting

   Echo response messages carry return codes and subcodes to indicate
   the result of the LSP Ping (when the ping mode is being used) as
   described in [RFC4379].

   When the responding node reports that it is an egress, it is clear
   that the echo response applies only to the reporting node. Similarly,
   when a node reports that it does not form part of the LSP described
   by the FEC (i.e. their is a misconnection) then the echo response
   applies to the reporting node.

   However, it should be noted that an echo response message that
   reports an error from a transit node may apply to multiple egress
   nodes (i.e. leaves) downstream of the reporting node. In the case of
   the Ping mode of operation, it is not possible to correlate the
   reporting node to the affected egresses unless the shape of the P2MP
   tree is already known, and it may be necessary to use the Traceroute
   mode of operation (see Section 3.3) to further diagnose the LSP.

   Note also that a transit node may discover an error but also
   determine that while it does lie on the path of the LSP under test,

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   it does not lie on the path to the specific egress being tested. In
   this case, the node SHOULD NOT generate an echo response.

   A reporting node that is a branch node may need to report multiple
   different errors (for different downstream branches). This is
   discussed further in Section 3.3.6.

3.3. Traceroute Mode Operation

   The traceroute mode of operation is described in [RFC4379]. Like
   other traceroute operations, it relies on the expiration of the TTL
   of the packet that carries the echo request. Echo requests may
   include a Downstream Mapping TLV, and when the TTL expires the echo
   request is passed to the control plane on the transit node which
   responds according to the Response Type in the message. A responding
   node fills in the fields of the Downstream Mapping TLV to indicate
   the downstream interfaces and labels used by the reported LSP from
   the responding node. In this way, by successively sending out echo
   requests with increasing TTLs, the ingress may gain a picture of the
   path and resources used by an LSP up to the point of failure when no
   response is received, or an error response is generated by a node
   where the control plane does not expect to be handling the LSP.

   This mode of operation is equally applicable to P2MP MPLS TE LSPs
   as described in the following sections.

   The traceroute mode can be applied to all destinations of the P2MP
   tree just as in the ping mode. In the case of P2MP MPLS TE LSPs, the
   traceroute mode can also be applied to individual traceroute targets
   identified by the presence of a P2MP Responder Identifier TLV. These
   targets may be egresses or transit nodes. However, since a transit
   node of a multicast LDP LSP is unable to determine whether it lies on
   the path to any one destination or any other transit node, the
   traceroute mode limited to specific nodes of such an LSP MUST NOT be
   used.

   Note that the addresses specified in the P2MP Responder Identifier
   TLV need not be egresses: they could be transit nodes on the LSP. The
   processing rules here and in the following sections apply equally to
   egress and transit nodes.

   In the absence of a P2MP Responder Identifier TLV, the echo request
   is asking for traceroute information applicable to all egresses.

   The echo response jitter technique described for the ping mode is
   equally applicable to the traceroute mode and is not additionally
   described in the procedures below.




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3.3.1. Traceroute Responses at Non-Branch Nodes

   When the TTL for the MPLS packet carrying an echo request expires the
   packet MUST be passed to the control plane as specified in [RFC4379].
   If the LSP under test is a multicast LDP LSP and if the echo request
   carries a P2MP Responder Identifier TLV the node MUST treat the echo
   request as malformed and MUST process it according to the rules
   specified in [RFC4379].

   Otherwise, the node MUST NOT return an echo response unless the
   responding node lies on the path of the P2MP LSP to the node (egress
   or transit) identified by the P2MP Responder Identifier TLV carried
   on the request, or if no such sub-TLV is present.

   If sent, the echo response MUST identify the next hop of the path of
   the LSP in the data plane by including a Downstream Mapping TLV as
   described in [RFC4379].

3.3.1.1. Correlating Traceroute Responses

   When traceroute is being simultaneously applied to multiple
   responders (e.g., egresses), it is important that the ingress should
   be able to correlate the echo responses with the branches in the P2MP
   tree. Without this information the ingress will be unable to
   determine the correct ordering of transit nodes. One possibility is
   for the ingress to poll the path to each responder in turn, but this
   may be inefficient, undesirable, or (in the case of multicast LDP
   LSPs) illegal.

   The Downstream Mapping TLV that MUST be included in the echo response
   indicates the next hop from each responding node, and this
   information supplied by a non-branch node can be pieced together by
   the ingress to reconstruct the P2MP tree although it may be necessary
   to refer to the routing information distributed by the IGP to
   correlate next hop addresses and node reporting addresses in
   subsequent echo responses.

   In order to facilitate more easy correlation of echo responses, the
   Downstream Mapping TLV can also contain Multipath Information as
   described in [RFC4379] to identify to which responders (transit
   nodes or egresses) the echo response applies. This information:

   - Cannot be present when the information is not known by the
     responding node. For example, for a multicast LDP LSP, the branch
     node will not know through normal LDP signaling which leaf nodes
     lie on which downstream branch.

   - SHOULD be present when the information is known by the responding
     node. That is for P2MP MPLS TE LSPs when the echo request applies
     to all egresses or to a specific single transit node or egress.

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   The format of the information in the Downstream Mapping TLV for
   P2MP MPLS LSPs is described in section 3.3.5.

3.3.2.  Traceroute Responses at Branch Nodes

   A branch node may need to identify more than one downstream interface
   in a traceroute echo response if some of the nodes identified in the
   P2MP Responder Identifier TLV that are being traced lie on different
   branches. This will always be the case for any branch node if all
   egresses are being traced.

   [RFC4379] describes how multiple Downstream Mapping TLVs should be
   included in an echo response, each identifying exactly one downstream
   interface that is applicable to the LSP.

   A branch node MUST follow the procedures described in Section 3.3.1
   to determine whether it should respond to an echo request. The branch
   node MUST add a Downstream Mapping TLV (or Downstream Detailed
   Mapping TLV - see Section 3.3.7) to the echo response for each
   outgoing branch that it reports, but it MUST NOT report branches that
   do not lie on the path to one of the destinations being traced. Thus
   a branch node may sometimes only need to respond with a single
   Downstream Mapping TLV; for example, consider the case where the
   traceroute is directed to only a single egress node. Therefore,
   the presence of only one Downstream Mapping TLV in an echo response
   does not guarantee that the reporting node is not a branch node.

   To report on its branching properties on a particular LSP, the
   responding node MAY include an optional TLV called the Node
   Properties TLV. This new TLV (see Section 3.3.2.1) can carry sub-
   TLVs, one of which (the Branching Properties sub-TLV - see Section
   3.3.2.2) allows the reporting node to describe the branching
   characteristics of the LSP at the reporting node.

3.3.2.1. Node Properties TLV

   A new TLV has been added to the set of optional TLVs that may be
   carried on an echo response message.

        Type #   Value Field
        ------   ------------

        TBD      Node properties

   The Node Properties TLV MAY be included in an echo response message.
   If more than one such TLV is present, the first MUST be processed and
   subsequent instances SHOULD be ignored.

   The Node Properties TLV is used to report characteristics of the
   reporting node, and the LSP at that node. This distinguishes it from

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   the Downstream Mapping TLV [RFC4379] and the Downstream Detailed
   Mapping TLV [DDMT] used to report characteristics of specific out-
   segments an LSP.

   The Node Properties TLV is a standard LSP Ping TLV as defined in
   [RFC4379]. It has the following format.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     :                                                               :
     :                        First Sub-TLV                          :
     :                                                               :
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                                                               ~
     ~                       Further Sub-TLVs                        ~
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The content of the Node Properties TLV is a series of one or more
   sub-TLVs. The Nore Properties TLV SHOULD contain one or more sub-TLVs
   and MUST be ignored if there are no sub-TLVs present.

   Each sub-TLV consists of the following fields as per [RFC4379]:

   - Two octet Type field: A value indicating the sub-TLV type.

   - Two octet Length field: A value indicating the total length of the
     Value field.

   - A Value field carrying the data of the sub-TLV. The content of the
     Value field is padded to a four byte boundary with zero-filled
     octets so that the Length field is always a multiple of 4.

3.3.2.2. Branching Properties Sub-TLV

   This document defines the Branching Properties sub-TLV carried in the
   Node Properties TLV. The Branching Properties sub-TLV is optional. If
   more than one such sub-TLV is found in a Node Properties TLV, the
   first MUST be processed and subsequent instances SHOULD be ignored.
   The sub-TLV may be used for P2MP and P2P LSPs.

   The Branching Properties sub-TLV is formed as described in Section
   3.3.2.1. The Value field has the following format.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Downstream Branch Count    |         Egress Count          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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   Downstream Branch Count

     This field reports the number of downstream branches from the
     reporting node for this LSP. The number may be zero for an egress,
     one for a non-branch node, and more than one for a branch node.
     Note that the value reported here may be greater than the number
     of Downstream Mapping TLVs present in the echo response message
     since those TLVs only report on the specific egresses queried. This
     value may be of use in detecting faults caused by delay introduced
     by the data replication mechanism at branch nodes.

   Egress Count

     This field reports the number of egresses local to the reporting
     node. Thus, for non-zero values the reporting node is either a leaf
     or a bud. When the value reported is non-zero, the reporting node
     MAY also include an Egress Address Sub-TLV for each local egress
     (see Section 3.3.2.3).

   For example, a branch node that has two downstream next hops on the
   LSP and that also delivers payload data to one local egress would set
   the two fields to 2 and 1 respectively.

3.3.2.3. Egress Address Sub-TLV

   This document defines the IPv4 and IPv6 Egress Address sub-TLVs
   carried in the Node Properties TLV. These TLVs are optional, and more
   than one instance of the sub-TLVs may legitimately be present.

   The Egress Address sub-TLVs are formed as described in Section
   3.3.2.1. The Value field has the following formats.

   IPv4 Egress Address Sub-TLV

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       IPv4 Egress Address                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IPv6 Egress Address Sub-TLV

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       IPv6 Egress Address                     |
     |                          (16 octets)                          |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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   The Egress Address sub-TLVs are optional. They MAY be included in a
   Node Properties TLV when reporting node is an egress (leaf or bud)
   for the LSP being tested. The sub-TLV may be used for P2MP and P2P
   LSPs.

   When one or more Egress Address sub-TLVs are present and the Branch
   Properties sub-TLV is also present, the value of the Egress Count
   field in the Branch Properties sub-TLV SHOULD be the same as the
   number of Egress Address sub-TLVs.

   The address contained in an Egress Address sub-TLV is the egress
   address to which the data is delivered. If there is just one egress
   and if the egress address is the same as the local node address
   carried in the main echo response message, both the Branching
   Properties sub-TLV and the Egress Address sub-TLV MAY be omitted as
   in legacy LSP Ping implementations.

3.3.2.4. Correlating Traceroute Responses

   Just as with non-branches, it is important that the echo responses
   from branch nodes provide correlation information that will allow the
   ingress to work out to which branch of the LSP the response applies.

   The P2MP tree can be determined by the ingress using the identity of
   the reporting node and the next hop information from the previous
   echo response, just as with echo responses from non-branch nodes.

   As with non-branch nodes, in order to facilitate more easy
   correlation of echo responses, the Downstream Mapping TLV can also
   contain Multipath Information as described in [RFC4379] to identify
   to which nodes the echo response applies. This information:

   - Cannot be present when the information is not known by the
     responding node. For example, for a multicast LDP LSP, the branch
     node will not know through normal LDP signaling which leaf nodes
     lie on which downstream branch.

   - SHOULD be present when the information is known by the responding
     node. That is for P2MP MPLS TE LSPs when the echo request applies
     to all egresses or to a specific single transit node or egress.

   The format of the information in the Downstream Mapping TLV for
   P2MP MPLS LSPs is described in section 3.3.5.

3.3.3. Traceroute Responses at Bud Nodes

   Some nodes on a P2MP MPLS LSP may be egresses, but also have
   downstream node. Such nodes are known as bud nodes [RFC4461].

   A bud node MUST respond to a traceroute echo request just as a branch

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   node would, but it MUST also indicate to the ingress that it is an
   egress in its own right. The issue to be resolved here is how to
   indicate that the reporting node is an egress when it is also
   providing one or more Downstream Mapping TLVs that indicate that it
   has downstream neighbors.

   This is achieved by the inclusion of a Node Properties TLV with a
   Branch Properties sub-TLV indicating the number of local egresses and
   the number of downstream branches. The bud node MAY also include one
   or more Egress Address sub-TLVs in the Node Properties TLV to report
   on the local egresses.

3.3.4. Non-Response to Traceroute Echo Requests

   The nature of P2MP MPLS TE LSPs in the data plane means that
   traceroute echo requests may be delivered to the control plane of
   nodes that must not reply to the request because, although they lie
   on the P2MP tree, they do not lie on the path to the node that is
   being traced.

   Thus, a node on a P2MP MPLS LSP MUST NOT respond to an echo request
   when the TTL has expired if any of the following applies:

   - The Reply Type indicates that no reply is required [RFC4379]

   - There is a P2MP Responder Identifier TLV present on the echo
     request (which means that the LSP is a P2MP MPLS TE LSP), but the
     address does not identify a node that is reached through this node
     for this particular P2MP MPLS LSP.

   Note that when no response to an echo request is received by the
   ingress (perhaps because the transit node has failed, or perhaps
   because the transit node does not support LSP Ping), then as per
   [RFC4379] the subsequent echo request (with a larger TTL) SHOULD be
   sent with Downstream Mapping TLV "Downstream IP Address" field set to
   the ALLROUTERs multicast address until a reply is received with a
   Downstream Mapping TLV.

3.3.5. Additions to Downstream Mapping Multipath Information

   A new value for the Multipath Type is defined to indicate that the
   reported Multipath Information applies to a P2MP MPLS TE LSP and may
   contain a list of node identifiers that indicate the egress nodes and
   (in the case where the P2MP Responder Identifier TLV was used on the
   echo request to identify non-egress nodes) transit nodes that can be
   reached through the reported interface. This Multipath Type MUST NOT
   be used for a multicast LDP LSP.




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      Type #    Address Type          Multipath Information
      ---       ----------------      ------------------------------
      TBD       P2MP responders       List of reachable P2MP nodes

   Note that a list of nodes may include IPv4 and IPv6 identifiers since
   these may be mixed in the P2MP MPLS TE LSP.

   The Multipath Length field continues to identify the length of the
   Multipath Information just as in [RFC4379] (that is, not including
   the downstream labels), and the downstream label (or potential stack
   thereof) is also handled just as in [RFC4379]. The format of the
   Multipath Information for a Multipath Type of P2MP responders is as
   follows.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Address Type  |   Responder Address  (4 or 16 octets)         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | (continued)   |                                               :
      +-+-+-+-+-+-+-+-+                                               :
      :              Further Address Types and Responder Addresses    :
      :                                                               :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Address Type

        This field indicates whether the address that follows is an IPv4
        or IPv6 address, and so implicitly encodes the length of the
        address.

        Two values are defined and mirror the values used in the Address
        Type field of the Downstream Mapping TLV itself.

          Type #        Address Type
          ------        ------------
               1        IPv4
               3        IPv6

      Responder Address

        An egress or transit node of this P2MP MPLS TE LSP that is
        reached through the interface indicated by the Downstream
        Mapping TLV and for which the traceroute echo request was
        enquiring.

   Note that padding to ensure that the whole Multipath information is
   aligned to a four-octet boundary is applied only after the last
   responder address in the list. That is, each successive Address Type
   follows on immediately after the previous Responder Address.

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3.3.6. Echo Response Reporting

   Echo responses are generated in response to traceroute echo requests
   at transit, branch, and bud nodes as described in Sections 3.3.1,

   3.3.2, and 3.3.3, while egress responses are as described in
   [RFC4379].

   Note, however, that a branch or bud node may have multiple downstream
   branches, and a transit node may have multiple downstream egresses
   (reached on the same branch). It may be the case that different
   conditions need to be reported for different branches or egresses.
   The echo response message defined in [RFC4379] has space for only a
   single return code and subcode pair, so where more than one return
   condition is reported by a single node it acts as follows.

   - It SHOULD use the Downstream Detailed Mapping TLV [DDMT] in place
     of the Downstream Mapping TLV, and encode the return code as
     described in Section 3.3.6.1.

   - It MAY report each condition in a separate echo response in which
     case MUST limit the downstream mapping information on each echo
     response to those branches/egresses to which the response applies.
     The use of multiple echo response messages to report errors might
     cause issues for an initiator that does not know how many responses
     it should wait for. For that reason, multiple messages should be
     used with care.

3.3.6.1. Reporting Multiple Conditions Using The DDM TLV

   When multiple different return codes are indicated on a single echo
   response message they MUST be carried in separate instances on the
   Downstream Detailed Mapping (DDM) TLV [DDMT]. That is, each instance
   of a DDM TLV carries one return code, and all information carried in
   that TLV MUST be limited to branches/egresses to which that return
   code applies. However, more than one DDM TLV on the same echo
   response MAY carry the same return code.

   The echo response message still carries a Return Code and a Return
   Subcode field. In order to clearly indicate that the relevant return
   codes are carried in the DDM TLV, a new return code is defined to be
   carried in the Return Code field of the echo response message as
   follows:

          Value    Meaning
          -----    -------
           TBD      See DDM TLV for more details

   The Return Subcode for this Return Code MUST be set to zero and
   MUST be ignored.

Yasukawa and Farrel                                            [Page 24]

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   The DDM TLV is defined as carrying a set of sub-TLVs. A new sub-TLV,
   the Return Code sub-TLV, is defined here to carry a return code and
   return subcode.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Return Code  | Return Subcode|           Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The length of the Return Code sub-TLV is 8.

   Return Code
     As defined for inclusion in the echo response message in [RFC4379].

   Return Subcode
     As defined for inclusion in the echo response message in [RFC4379].

   Reserved
     SHOULD be set to zero on transmission and MUST be ignored on
     receipt.

   If the Return Code of the echo response message is not set to "See
   DDM TLV for more details" then any Return Code sub-TLV present in a
   DDM TLV SHOULD be ignored.

   If the Return Code of the echo response message is set to "See DDM
   TLV for more details" then a Return Code sub-TLV MUST be present in
   each DDM TLV. Subsequent Return Code sub-TLVs present in the same DDM
   TLV SHOULD be ignored.

4. Operation of LSP Ping for Bootstrapping Other OAM Mechanisms

   Bootstrapping of other OAM procedures can be achieved using the
   MPLS Echo Request/Response messages. The LSP(s) under test are
   identified using the RSVP P2MP IPv4 or IPv6 Session sub-TLVs
   (see Section 3.1.1) or the Multicast LDP FEC Stack sub-TLV
   (see Section 3.1.2).

   Other sub-TLVs may be defined in other specifications to indicate
   the OAM procedures being bootstrapped, and to describe the bootstrap
   parameters. Further details of the bootstrapping processes and the
   bootstrapped OAM processes are described in other documents. For
   example, see [MPLS-BFD] and [MCAST-CV].







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5. Non-compliant Routers

   If an egress for a P2MP LSP does not support MPLS LSP ping, then no
   reply will be sent, resulting in a "false negative" result. There is
   no protection for this situation, and operators may wish to ensure
   that end points for P2MP LSPs are all equally capable of supporting
   this function. Alternatively, the traceroute option can be used to
   verify the LSP nearly all the way to the egress, leaving the final
   hop to be verified manually.

   If, in "traceroute" mode, a transit node does not support LSP ping,
   then no reply will be forthcoming from that node for some TTL, say n.
   The node originating the echo request SHOULD continue to send echo
   request with TTL=n+1, n+2, ..., n+k to probe nodes further down the
   path. In such a case, the echo request for TTL > n SHOULD be sent
   with Downstream Mapping TLV "Downstream IP Address" field set to the
   ALLROUTERs multicast address as described in Section 3.3.4 until a
   reply is received with a Downstream Mapping TLV.

6. OAM Considerations

   The procedures in this document provide OAM functions for P2MP MPLS
   LSPs and may be used to enable bootstrapping of other OAM procedures.

   In order to be fully operational several considerations must be made.

   - Scaling concerns dictate that only cautious use of LSP Ping should
     be made. In particular, sending an LSP Ping to all egresses of a
     P2MP MPLS LSP could result in congestion at or near the ingress
     when the responses arrive.

     Further, incautious use of timers to generate LSP Ping echo
     requests either in ping mode or especially in traceroute may lead
     to significant degradation of network performance.

   - Management interfaces should allow an operator full control over
     the operation of LSP Ping. In particular, it SHOULD provide the
     ability to limit the scope of an LSP Ping echo request for a P2MP
     MPLS LSP to a single egress.

     Such an interface SHOULD also provide the ability to disable all
     active LSP Ping operations to provide a quick escape if the network
     becomes congested.

   - A MIB module is required for the control and management of LSP Ping
     operations, and to enable the reported information to be inspected.

     There is no reason to believe this should not be a simple extension
     of the LSP Ping MIB module used for P2P LSPs.


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7. IANA Considerations

7.1. New Sub-TLV Types

   Three new sub-TLV types are defined for inclusion within the LSP Ping
   [RFC4379] Target FEC Stack TLV (TLV type 1).

   IANA is requested to assign sub-type values to the following
   sub-TLVs from the "Multiprotocol Label Switching Architecture (MPLS)
   Label Switched Paths (LSPs) Parameters - TLVs" registry, "TLVs and
   sub-TLVs" sub-registry.

     RSVP P2MP IPv4 Session (see Section 3.1.1). Suggested value 17.
     RSVP P2MP IPv6 Session (see Section 3.1.1). Suggested value 18.
     Multicast LDP FEC Stack (see Section 3.1.2). Suggested value 19.

7.2. New Multipath Type

   Section 3.3 of [RFC4379] defines a set of values for the LSP Ping
   Multipath Type. These values are currently not tracked by IANA.

   A new value for the LSP Ping Multipath Type is defined in Section
   3.3.5 of this document to indicate that the reported Multipath
   Information applies to a P2MP MPLS TE LSP.

   IANA is requested to create a new registry as follows:

   "Multiprotocol Label Switching Architecture (MPLS) Label Switched
   Paths (LSPs) - Multipath Types"

   Key   Type                  Multipath Information
   ---   ----------------      ---------------------
     0    no multipath          Empty (Multipath Length = 0)   [RFC4379]
     2    IP address            IP addresses                   [RFC4379]
     4    IP address range      low/high address pairs         [RFC4379]
     8    Bit-masked IP         IP address prefix and bit mask [RFC4379]
            address set
     9    Bit-masked label set  Label prefix and bit mask      [RFC4379]
    xx    P2MP responder IP     List of P2MP responders        [thisDoc]
            addresses

    A suggested value of xx is 16.

    New values from this registry are to be assigned only by Standards
    Action.






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7.3. New TLVs

   Three new LSP Ping TLV types are defined for inclusion in LSP Ping
   messages.

   IANA is requested to assign a new value from the "Multi-Protocol
   Label Switching Architecture (MPLS) Label Switched Paths (LSPs)
   Parameters - TLVs" registry, "TLVs and sub-TLVs" sub-registry as
   follows using a Standards Action value.
     P2MP Responder Identifier TLV (see Section 3.2.4) is a mandatory
     TLV. Suggested value 11.

       Two sub-TLVs are defined
       - Type 1: IPv4 P2MP Responder Identifier (see Section 3.2.4)
       - Type 2: IPv6 P2MP Responder Identifier (see Section 3.2.4)

     Echo Jitter TLV (see Section 3.2.5) is a mandatory TLV. Suggested
     value 12.

     Node Properties TLV (see Section 3.2.2.1) is an optional TLV.
     Suggested value 32768.
       Three sub-TLVs are defined
       - Type 1: IPv4 Egress Address
       - Type 2: IPv6 Egress Address
       - Type 3: Branch Properties

7.4. New Return Code

   A new Return Code is defined in Section 3.3.6.1.

   IANA is requested to assign a new Return Code value for the "Multi-
   Protocol Label Switching (MPLS) Label Switched Paths (LSPs)
   Parameters" registry, "Return Codes" sub-registry as follows using a
   Standards Action value.

          Value    Meaning
          -----    -------
           TBD      See DDM TLV for more details

   Suggested value 14.

7.5. New Sub-TLV Value for the Downstream Detailed Mapping TLV

   [DDMT] defines a TLV called the Downstream Detailed Mapping TLV and
   requests IANA to maintain a registry of sub-TLVs that it can carry.

   Section 3.3.6.1 of this document defines a new sub-TLV.

   IANA is requested to assign a TLV type value as follows using a
   Standards Action value from the range 0-32767.

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Internet Draft     draft-ietf-mpls-p2mp-lsp-ping-07.txt   September 2008

        Sub-Type    Value Field
        ---------   ------------
        TBD         Return Code

8. Security Considerations

   This document does not introduce security concerns over and above
   those described in [RFC4379]. Note that because of the scalability
   implications of many egresses to P2MP MPLS LSPs, there is a
   stronger concern to regulate the LSP Ping traffic passed to the
   control plane by the use of a rate limiter applied to the LSP Ping
   well-known UDP port. Note that this rate limiting might lead to
   false positives.

9. Acknowledgements

   The authors would like to acknowledge the authors of [RFC4379] for
   their work which is substantially re-used in this document. Also
   thanks to the members of the MBONED working group for their review
   of this material, to Daniel King and Mustapha Aissaoui for their
   review, and to Yakov Rekhter for useful discussions.

   The authors would like to thank Vanson Lim, Danny Prairie, Reshad
   Rahman, Ben Niven-Jenkins, Hannes Gredler, Nitin Bahadur, Tetsuya
   Murakami and Michael Hua for their comments and suggestions.

10. Intellectual Property Considerations

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard. Please address the information to the IETF at ietf-
   ipr@ietf.org.


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11. 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 Swallow, G., "Detecting Multi-Protocol
               Label Switched (MPLS) Data Plane Failures", RFC 4379,
               February 2006.

   [DDMT]      Bahadur, N., Kompella, K., and Swallow, G., "Mechanism
               for Performing LSP-Ping over MPLS Tunnels", draft-ietf-
               mpls-lsp-ping-enhanced-dsmap, work in progress.

12. Informative References

   [RFC792]    Postel, J., "Internet Control Message Protocol", RFC 792.

   [RFC4461]   Yasukawa, S., "Signaling Requirements for Point to
               Multipoint Traffic Engineered Multiprotocol Label
               Switching (MPLS) Label Switched Paths (LSPs)",
               RFC 4461, April 2006.

   [RFC4687]   Yasukawa, S., Farrel, A., King, D., and Nadeau, T.,
               "Operations and Management (OAM) Requirements for
               Point-to-Multipoint MPLS Networks", RFC 4687, September
               2006.

   [RFC4875]   Aggarwal, R., Papadimitriou, D., and Yasukawa, S.,
               "Extensions to Resource Reservation Protocol - Traffic
               Engineering (RSVP-TE) for Point-to-Multipoint TE Label
               Switched Paths (LSPs)", RFC 4875, May 2007.

   [P2MP-LDP-REQ] J.-L. Le Roux, et al., "Requirements for
               point-to-multipoint extensions to the Label Distribution
               Protocol", draft-ietf-mpls-mp-ldp-reqs, work in progress.

   [P2MP-LDP]  Minei, I., and Wijnands, I., "Label Distribution Protocol
               Extensions for Point-to-Multipoint and
               Multipoint-to-Multipoint Label Switched Paths",
               draft-ietf-mpls-ldp-p2mp, work in progress.

   [MCAST-CV]  Swallow, G., and Nadeau, T., "Connectivity Verification
               for Multicast Label Switched Paths",
               draft-swallow-mpls-mcast-cv, work in progress.

   [BFD]       Katz, D., and Ward, D., "Bidirectional Forwarding
               Detection", draft-ietf-bfd-base, work in progress.




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Internet Draft     draft-ietf-mpls-p2mp-lsp-ping-07.txt   September 2008

   [MPLS-BFD]  Aggarwal, R., Kompella, K., Nadeau, T., and Swallow, G.,
               "BFD For MPLS LSPs", draft-ietf-bfd-mpls, work in
               progress.

   [IANA-PORT] IANA Assigned Port Numbers, http://www.iana.org

13. Authors' Addresses

   Seisho Yasukawa
   NTT Corporation
   (R&D Strategy Department)
   3-1, Otemachi 2-Chome Chiyodaku, Tokyo 100-8116 Japan
   Phone: +81 3 5205 5341
   Email: s.yasukawa@hco.ntt.co.jp

   Adrian Farrel
   Old Dog Consulting
   EMail: adrian@olddog.co.uk

   Zafar Ali
   Cisco Systems Inc.
   2000 Innovation Drive
   Kanata, ON, K2K 3E8, Canada.
   Phone: 613-889-6158
   Email: zali@cisco.com

   Bill Fenner
   Arastra, Inc.
   275 Middlefield Rd.
   Suite 50
   Menlo Park, CA 94025
   Email: fenner@fenron.com

   George Swallow
   Cisco Systems, Inc.
   1414 Massachusetts Ave
   Boxborough, MA 01719
   Email: swallow@cisco.com

   Thomas D. Nadeau
   British Telecom
   BT Centre
   81 Newgate Street
   EC1A 7AJ
   London
   Email: tom.nadeau@bt.com





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14. Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.




































Yasukawa and Farrel                                            [Page 32]


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