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Versions: 00 01 02 03 04 05 06 07                                       
Network Working Group                                     George Swallow
Internet Draft                                       Cisco Systems, Inc.
Category: Standards Track
Expiration Date: April 2006
                                                        Kireeti Kompella
                                                  Juniper Networks, Inc.

                                                              Dan Tappan
                                                     Cisco Systems, Inc.

                                                            October 2005


                    Label Switching Router Self-Test


                  draft-ietf-mpls-lsr-self-test-06.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

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   Abstract

      This document defines a means for a Label-Switching Router (LSR)
      to verify that its data plane is functioning for certain key
      Multi-Protocol Label Switching (MPLS) applications, including
      unicast forwarding and traffic engineering tunnels.  A new



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      Loopback FEC type is defined to allow an upstream neighbor to
      assist in the testing at very low cost.  MPLS Verification Request
      and MPLS Verification Reply messages are defined to do the actual
      probing.



Contents

 1      Introduction  ..............................................   3
 1.1    Conventions  ...............................................   3
 2      Loopback FEC  ..............................................   4
 2.1    Loopback FEC Element  ......................................   4
 2.2    LDP Procedures  ............................................   5
 3      Data Plane Self Test  ......................................   6
 3.1    Data Plane Verification Request / Reply Messages  ..........   7
 3.2    UDP Port  ..................................................   8
 3.3    Reply-To Address Object  ...................................   8
 3.3.1  IPv4 Reply-To Address Object  ..............................   8
 3.3.2  IPv6 Reply-To Address Object  ..............................   9
 3.4    Sending procedures  ........................................   9
 3.5    Receiving procedures  ......................................  10
 3.6    Upstream Neighbor Verification  ............................  11
 4      Security Considerations  ...................................  12
 5      IANA Considerations  .......................................  12
 6      Acknowledgments  ...........................................  12
 7      References  ................................................  12
 7.1    Normative References  ......................................  12
 7.2    Informative References  ....................................  13
 8      Authors' Addresses  ........................................  13




















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1. Introduction

   This document defines a means for a Label-Switching Router (LSR) to
   verify that its data plane is functioning for certain key Multi-Pro-
   tocol Label Switching (MPLS) applications, including unicast forward-
   ing based on LDP [LDP] and traffic engineering tunnels based on
   [RSVP-TE].  MPLS Verification Request and MPLS Verification Reply
   messages are defined to do the actual probing.  The pings are sent to
   an upstream neighbor, looped back through the LSR under test and
   intercepted, by means of TTL expiration by a downstream neighbor.

   In order to minimize the load on upstream LSRs a loopback FEC Type is
   defined. Labels advertised with this FEC Type are referred to as
   loopback labels.  Receipt of a packet labeled with a loopback label
   will cause the advertising LSR to pop the label off the label stack
   and send the packet out the advertised interface.

   Use of a loopback mechnism allows an LSR to test label entries which
   are not currently in use.  For example many LSRs advertise label map-
   pings for all IPv4 routes to all of their neighbors.  For some por-
   tion of these their neighbor LSR is not currently upstream and the
   label entry is not used.  But if the neighbors best path to a desti-
   nation changes, that route and the associated label entry will be
   used.  An LSR can loop traffic through a "non-upstream" LSR because
   that LSR is acting only on the loopback label and not on the underly-
   ing label associated with the actual FEC being tested.  In this way
   label entries can be verified prior to the occurrence of a routing
   change.

   Some routing protocols, most notably OSPF have no means of exchanging
   the "Link Local Identifiers" used to identify unnumbered links and
   components of bundled links.  These test procedures can be used to
   associate the neighbor's interfaces with the probing LSRs interfaces.
   This is achieved by simply having the TTL of the MPLS Ping expire one
   hop sooner, i.e. at the testing LSR itself.



1.1. Conventions

   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 [KEYWORDS].








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2. Loopback FEC

   The Loopback FEC type is defined to enable an upstream neighbor to
   assist in LSR self-testing at very low cost.  This FEC causes the
   loopback to occur in the data plane without control plane involvement
   beyond the initial LDP exchange and data-plane setup.  The FEC also
   carries information to indicate the desired encapsulation should it
   be the only label in a received label stack.  Values are defined for
   IPv4 and IPv6.

   An LSR uses a Loopback FEC to selectively advertise loopback labels
   to its neighbor LSRs.  Each loopback label is bound to a particular
   interface.  For multi-access links, a unique label for each neighbor
   is required, since the link-level address is derived from the label
   lookup.  When an MPLS packet with its top label set to a loopback
   label is received from an interface over which that label was adver-
   tised, the loopback label is popped and the packet is sent on the
   interface to which the loopback label was bound.  If the label-stack
   only contains the one loopback label, the encapsulation of the packet
   is determined by the FEC Type.

   TTL treatment for loopback labels follows the Uniform model.  I.e.
   the TTL carried in the loopback label is decremented and copied to
   the exposed label or IP header as the case may be.



2.1. Loopback FEC Element

   FEC element type 130 is used.   The FEC element is encoded as fol-
   lows: (note: 130 is provisionally assigned, the actual value will be
   assigned by IANA.)


       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     130       |      Res      | If & Prot Type|   Id Length   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Interface Identifier                      |
      |                              "                                |
      |                              "                                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+








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      Reserved (Res)

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


      Interface & Protocol Type

            #     Type                 Interface Identifier
           ---    ----                 --------------------
            1     IPv4 Numbered        IPv4 Address
            2     IPv4 Unnumbered      A 32 bit Link Identifier as
                                         defined in [RFC3477]
            3     IPv6 Numbered        IPv6 Address
            4     IPv6 Unnumbered      A 32 bit Link Identifier as
                                         defined in [RFC3477]

         Note that these type values also indicate the encapsulation (IPv4 or
         IPv6) for payloads that have a label stack containing only a loopback
         label.



      Identifier Length

         Length of the interface identifier in octets.  The length is 4
         bytes for the unnumbered types and IPv4, 16 bytes for IPv6.

      Address

         An identifier encoded according to the Identifier Type field.


2.2. LDP Procedures

   It is RECOMMENDED that loopback labels only be distributed in
   response to a Label Request message, irrespective of the label adver-
   tisement mode of the LDP session.  However it is recognized that in
   certain cases such as OSPF with unnumbered links, the upstream LSR
   may not have sufficiently detailed information of the neighbor's link
   identifier to form the request.  In these cases, the downstream LSR
   MAY be configured to make unsolicited advertisements.










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3. Data Plane Self Test

   A self test operation involves three LSRs, the LSR doing the test, an
   upstream neighbor and a downstream LSR.  Upstream here is with
   respect to the flow of the test (which in some cases could be differ-
   ent than the normal sense of upstream in IP routing).  We refer to
   these as LSRs T, U, and D respectively.  In order to minimize the
   processing load on LSR-D, two new LSP Ping messages are defined,
   called the MPLS Data Plane Verification Request and the MPLS Data
   Plane Verification Reply.  These messages are used to allow LSR-T to
   obtain the label stack, address and interface information of LSR-D.

   The packet flow is shown below. Although the figure shows LSR-D adja-
   cent to LSR-T it may in some cases be an arbitrary number of hops
   away.


                 +-------+       +-------+       +-------+
                 |     ,-|-------|<DPVRq |       |       |
                 |     `-|-------|-------|-------|->     |
                 |       |       |       |       |       |
                 |       |       |     <-|-------|<DPVRp |
                 +-------+       +-------+       +-------+
                   LSR-U           LSR-T           LSR-D

               DPVRq: MPLS Data Plane Verification Request
               DPVRp: MPLS Data Plane Verification Reply

                    Figure 1: Self Test Message Flow


   In order to perform a test on an incoming label stack, LSR-T forms an
   MPLS Data Plane Verification Request.  LSR-T prepends the packet with
   the incoming label stack being tested and the loopback label received
   from LSR-U.  The TTL values are set such that they will expire at
   LSR-D.  LSR-T then forwards the packet to LSR-U.

   LSR-U receives the packet and performs normal MPLS forwarding.  That
   is, the loopback label is popped, the TTL is decremented and propa-
   gated (in this case) to the exposed label.

   LSR-T receives the packet and performs normal MPLS forwarding.  If
   everything is functioning as expected this will cause the packet to
   arrive at LSR-D with a TTL of 1.

   In this example, we assume that all is working properly.  The TTL
   expires at LSR-D causing it to receive the packet.   LSR-D notes the
   the interface and the label stack on which the packet was received



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   and records these in an Interface and Label Stack TLV.  This Object
   is sent to LSR-T in an MPLS Data Plane Verification Reply message.



3.1. Data Plane Verification Request / Reply Messages

   Two new LSP Ping messages are defined for LSR self test.  The purpose
   of the new messages is three fold.  First the timestamps are removed
   to minimize processing.  Second the message type allows simple recog-
   nition that minimal processing is necessary to service this request.
   Third, the Verification Request message itself conveys the the
   request, thus a Verification Request message with no Objects is both
   legal and normal.

   The definitions of all fields in the messages are identical to those
   found in [LSP-PING].

   The new message types are: (Provisionally; to be assigned)

      Type     Message
      ----     -------
        3      MPLS Data Plane Verification Request
        4      MPLS Data Plane Verification Reply

   The messages have 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Version Number        |         MUST Be Zero          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Message Type |   Reply mode  |  Return Code  | Return Subcode|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sender's Handle                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence Number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            TLVs ...                           |
   .                                                               .
   .                                                               .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+







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   The MPLS Data Plane Verification Request message MAY contain the fol-
   lowing objects:

          Type #                  Object
          ------                  -----------
               3                  Pad
              10                  Reply TOS Byte
              11 (provisional)    IPv4 Reply-to Address
              12 (provisional)    IPv6 Reply-to Address
           64512-65535            Vendor Private TLVs

   The MPLS Data Plane Verification Reply message MAY contain the fol-
   lowing objects:

          Type #                  Object
          ------                  -----------
               7                  Interface and Label Stack
               9                  Errored TLVs
           64512-65535            Vendor Private TLVs



3.2. UDP Port

   MPLS Data Plane Verification Request messages MAY be sent to port
   3503 as is used for [LSP-PING].  However to aid implementations that
   wish to handle these messages at a lower level than MPLS Echo Request
   messages another UDP port, <tbd>, is provided.  Port <tbd> SHOULD be
   used by default.  The source UDP port, as in [LSP-PING] is chosen by
   the sender.


3.3. Reply-To Address Object

   In order to perform detailed diagnostics of a particular failing flow
   in the face of ECMP, it is useful to be able to use the exact source
   and destination addresses of that flow.  The Reply-To Object is an
   optional TLV in a MPLS Data Plane Verification Request message.  The
   Object has two formats, type 11 for IPv4 and type 12 for IPv6 (to be
   assigned by IANA).


3.3.1. IPv4 Reply-To Address Object

   The length of an IPv4 Reply-to Address object is 4 octets; the value
   field has the following format:





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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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Reply-to IPv4 Address                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      Reply-to IPv4 Address

         The address to which the MPLS Data Plane Verification Reply
         message is to be sent.



3.3.2. IPv6 Reply-To Address Object

   The length of an IPv6 Reply-to Address object is 16 octets; 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Reply-to IPv6 Address                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Reply-to IPv6 Address (Cont.)                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Reply-to IPv6 Address (Cont.)                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Reply-to IPv6 Address (Cont.)                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Reply-to IPv6 Address

         The address to which the MPLS Data Plane Verification Reply
         message is to be sent.



3.4. Sending procedures

   In order to perform a test on an incoming labeled or unlabeled
   packet, an LSR first determines the expected outgoing label stack,
   next hop router and next hop interface.

   The LSR creates an MPLS Data Plane Verification Request message.

   In normal use, the source address is set to an address belonging to
   the LSR and the destination set to an address in the range of 127/8.



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   The incoming label stack (if any) is prepended to the packet.  The
   TTL of these labels and the packet header SHOULD be set to appropri-
   ate values - 2 for those labels and/or header which will be processed
   by this node when the packet is looped back; 1 for those labels
   and/or header which will be carried through.  Finally the loopback
   label bound to the incoming interface is prepended to the packet.  In
   the case of an otherwise unlabeled packet the label's FEC MUST indi-
   cate the appropriate IP version.  The TTL is set such that it will
   have the value of 3 on the wire.

   The packet is sent to the upstream neighbor on an interface for which
   the loopback label is valid.

   In diagnostic situations, the source and destination addresses MAY be
   set to any value.  In this case, a Reply-to IPv4 or IPv6 Address
   object MUST be included.  The IP TTL MUST be set to 1.  The TTL of
   labels other than the loopback label MUST be set to appropriate val-
   ues - 2 for those labels which will be process by this LSR when the
   packet is looped back; 1 for those labels which will be carried
   through.

   In some MPLS deployments TTL hiding is used to make a providers net-
   work appear as a single hop.  That is the TTL in the imposed label
   does not reflect the TTL of the received packet.  It is RECOMMENDED
   that testing of label imposition SHOULD NOT be performed in such cir-
   cumstances as the Verification Request will in most case travel mul-
   tiple hops.


3.5. Receiving procedures

   An LSR X that receives an MPLS Verification Request message formats a
   MPLS Verification Reply message.  The Sender's Handle and Sequence
   Number are copied from the Request message.

   X then parses the packet to ensure that it is a well-formed packet,
   and that the TLVs that are not marked "Ignore" are understood.  If
   not, X SHOULD set the Return Code set to "Malformed echo request
   received" or "TLV not understood" (as appropriate), and the Subcode
   set to zero.  In the latter case, the misunderstood TLVs (only) are
   included in the reply.

   If the Verification Request is good, X MUST note the interface and
   label stack of the received Verification Request and format this
   information as a Downstream Verification object.  This object is
   included in the MPLS Verification Reply message.  The Return Code and
   Subcode MUST be set to zero, indicating "No return code".




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   The source address of the Reply message MUST be an address of the
   replying LSR.  If the request included a Reply-to IPv4 or IPv6
   Address object, the MPLS Data Plane Verification Reply message MUST
   be sent to that address.  Otherwise the Reply message is sent to the
   source address of the Verification Request message.

   An LSR MUST be capable of filtering addresses that are to be replied
   to.  If a filter has been invoked (i.e. configured) and an address
   does not pass the filter, then a reply MUST NOT be sent, and the
   event SHOULD be logged.


3.6. Upstream Neighbor Verification

   To verify that an upstream neighbor is properly echoing packets an
   LSR may send an MPLS Data Plane Verification Request packet with the
   TTL set so that the packet will expire upon reaching reaching itself.
   This procedure not only tests that the neighbor is correctly process-
   ing the loopback label, it also allows the node to verify the neigh-
   bor's interface mapping.


                      +-------+       +-------+
                      |       |       |       |
                      |     ,-|-------|<DPVRq |
                      |     `-|-------|->     |
                      |       |       |       |
                      +-------+       +-------+
                        LSR-U           LSR-T

             DPVRq: MPLS Data Plane Verification Request


              Figure 2: Upstream Neighbor Verification

   No TLVs need to be included in the MPLS Data Plane Verification
   Request.  By noting the Sender's Handle and Sequence Number, as well
   as the loopback label, LSR-T is able to detect that a) the packet was
   looped, and b) determine (or verify) the interface on which the
   packet was received.











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4. Security Considerations

   Were loopback labels widely known, they might be subject to abuse.
   It is therefore RECOMMENDED that loopback labels only be shared
   between trusted neighbors.  Further, if the loopback labels are drawn
   from the Global Label Space, or any other label space shared across
   multiple LDP sessions, it is RECOMMENDED that all loopback labels be
   filtered from a session except those labels pertaining to interfaces
   directly connected to the neighbor participating in that session.



5. IANA Considerations

   This document makes the following codepoint assigments (pending IANA
   action):

       Registry             Codepoint    Purpose

       UDP Port                tbd       MPLS Verification Request

       LSP Ping Message Type    3        MPLS Data Plane Verification
                                           Request
       LSP Ping Message Type    4        MPLS Data Plane Verification
                                           Reply
       LSP Ping Object Type    11        IPv4 Reply-to Address
       LSP Ping Object Type    12        IPv6 Reply-to Address



6. Acknowledgments

   The authors would like to thank Vanson Lim, Tom Nadeau, and Bob
   Thomas for their comments and suggestions.



7. References

7.1. Normative References

   [RFC3036]  Andersson, L. et al., "LDP Specification", January 2001.

   [LSP-Ping] Bonica, R. et al., "Detecting MPLS Data Plane Liveness",
              work-in-progress.

   [RFC3477]  Kompella, K. & Y. Rekhter, "Signalling Unnumbered Links
              in Resource ReSerVation Protocol - Traffic Engineering



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              (RSVP-TE)", January 2003.

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


7.2. Informative References

   [RSVP-TE]  Awduche, D., et al, "RSVP-TE: Extensions to RSVP for LSP
              tunnels", RFC 3209, December 2001.



8. Authors' Addresses

      Kireeti Kompella
      Juniper Networks, Inc.
      1194 N. Mathilda Ave.
      Sunnyvale, CA 94089
      Email:  kireeti@juniper.net


      George Swallow
      Cisco Systems, Inc.
      1414 Massachusetts Ave
      Boxborough, MA 01719

      Email:  swallow@cisco.com


      Dan Tappan
      Cisco Systems, Inc.
      1414 Massachusetts Ave
      Boxborough, MA 01719

      Email:  tappan@cisco.com



Copyright Notice

   Copyright (C) The Internet Society (2005).  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.







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Expiration Date

   April 2006


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