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Versions: 00 01 02 03 04 draft-ietf-mpls-entropy-lsp-ping

Internet Engineering Task Force                                 N. Akiya
Internet-Draft                                                G. Swallow
Updates: 4379,6790 (if approved)                            C. Pignataro
Intended status: Standards Track                           Cisco Systems
Expires: April 24, 2014                                 October 21, 2013


         Label Switched Path (LSP) Ping/Trace over MPLS Network
                       using Entropy Labels (EL)
                  draft-akiya-mpls-entropy-lsp-ping-00

Abstract

   The Multiprotocol Label Switching (MPLS) Label Switched Path (LSP)
   Ping and Traceroute are used to exercise specific paths of Equal Cost
   Multipath (ECMP).  This ability has been lost on some scenarios which
   makes use of [RFC6790]: Entropy Labels (EL).

   This document extends the MPLS LSP Ping and Traceroute mechanisms to
   restore the ability of exercising specific paths of ECMP over LSP
   which make use of Entropy Label.  This document updates [RFC4379] and
   [RFC6790].

Requirements Language

   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].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 24, 2014.

Copyright Notice




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   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Multipath Type 9  . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Initiating LSR Procedures . . . . . . . . . . . . . . . . . .   6
   5.  Responder LSR Procedures  . . . . . . . . . . . . . . . . . .   7
     5.1.  IP Based Load Balancer & Not Imposing ELI/EL  . . . . . .   7
     5.2.  IP Based Load Balancer & Imposing ELI/EL  . . . . . . . .   8
     5.3.  Label Based Load Balancer & Not Imposing ELI/EL . . . . .   8
     5.4.  Label Based Load Balancer & Imposing ELI/EL . . . . . . .   9
     5.5.  FAT MS-PW Stitching LSR . . . . . . . . . . . . . . . . .   9
   6.  Entropy Label FEC . . . . . . . . . . . . . . . . . . . . . .  10
   7.  DS Flags: L and E . . . . . . . . . . . . . . . . . . . . . .  10
   8.  New Multipath Information Type: 10  . . . . . . . . . . . . .  11
   9.  Unsupported Cases . . . . . . . . . . . . . . . . . . . . . .  13
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  13
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     11.1.  DS Flags . . . . . . . . . . . . . . . . . . . . . . . .  13
     11.2.  Multipath Information Types  . . . . . . . . . . . . . .  13
     11.3.  Entropy Label FEC  . . . . . . . . . . . . . . . . . . .  13
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   13. Contributing Authors  . . . . . . . . . . . . . . . . . . . .  14
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     14.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction









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   Section 3.3.1 of [RFC4379] specifies multipath information encoding
   which can be used by LSP Ping initiator to trace and validate all
   ECMP paths between ingress and egress.  These encodings are
   sufficient when all the LSRs along the path(s), between ingress and
   egress, consider same set of "keys" as input for load balancing
   algorithm: all IP based or all label based.

   With introduction of [RFC6790], it is quite normal to see set of LSRs
   performing load balancing based on EL/ELI while others still follow
   the traditional way (IP based).  This results in LSP Ping initiator
   not be able to trace and validate all ECMP paths in following
   scenarios:

   o  One or more transit LSRs along ELI/EL imposed LSP do not perform
      ECMP load balancing based on EL (hashes based on "keys" including
      IP destination address).  This scenario is not only possible but
      quite common due transit LSRs not implementing [RFC6790] or
      transit LSRs implementing [RFC6790] but not implementing suggested
      transit LSR behavior in Section 4.3 of [RFC6790].

   o  Two or more LSPs stitched together with at least one LSP being ELI
      /EL imposing LSP.  Such scenarios are described in
      [I-D.ravisingh-mpls-el-for-seamless-mpls].

   These scenarios will be quite common because every deployment of
   [RFC6790] will invariably end up with nodes that support ELI/EL and
   nodes that do not.  There will typically be areas that support ELI/EL
   and areas that do not.

   As pointed out in [RFC6790] the procedures of [RFC4379] with respect
   to multipath information type {9} are incomplete.  However [RFC6790]
   does not actually update [RFC4379].  Further the specific EL location
   is not clearly defined, particularly in the case of FAT Pseudowires
   [RFC6391].  Herein is defined a new FEC Stack sub-TLV for the Entropy
   Label.  Section 3 of this document updates the procedures for
   multipath information type {9}.

2.  Overview

   [RFC4379] describes LSP traceroute as an operation performed through
   initiating LSR sending LSP Ping packet (LSP echo request) with
   incrementing TTL, starting with TTL of one.  Initiating LSR discovers
   and exercises ECMP by obtaining multipath information from each
   transit LSR and using specific destination IP address or specific
   entropy label.

   LSP Ping initiating LSR sends LSP echo request with multipath
   information.  This multipath information is described in DSMAP/DDMAP



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   TLV of echo request, and can contain set of IP addresses or set of
   labels today.  Multipath information types {2, 4, 8} carry set of IP
   addresses and multipath information type {9} carries set of labels.
   Responder LSR (receiver of LSP echo request) is to determine subset
   of initiator specified multipath information which load balances to
   each downstream (outgoing interface).  Responder LSR sends LSP echo
   reply with resulting multipath information per downstream (outgoing
   interface) back to the initiating LSR.  Initiating LSR is then able
   to use specific IP destination address or specific label to exercise
   specific ECMP path on the responder LSR.

   Current behavior is problematic in following scenarios:

   o  Initiating LSR sends IP multipath information, but responder LSR
      load balances on labels.

   o  Initiating LSR sends label multipath information, but responder
      LSR load balances on IP addresses.

   o  Initiating LSR sends any of existing multipath information to ELI/
      EL imposing LSR, but initiating LSR can only continue to discover
      and exercise specific path of ECMP if ELI/EL imposing LSR responds
      with both IP addresses and associated EL corresponding to each IP
      address.  This is because:

      *  ELI/EL imposing LSR that is a stitching point will load balance
         based on IP address.

      *  Downstream LSR(s) of ELI/EL imposing LSR may load balance based
         on ELs.

   o  Initiating LSR sends any of existing multipath information to ELI/
      EL imposing LSR, but initiating LSR can only continue to discover
      and exercise specific path of ECMP if ELI/EL imposing LSR responds
      with both labels and associated EL corresponding to label.  This
      is because:

      *  ELI/EL imposing LSR that is a stitching point will load balance
         based on EL from previous LSP and imposes new EL.

      *  Downstream LSR(s) of ELI/EL imposing LSR may load balance based
         on new ELs.

   The above scenarios point to how the existing multipath information
   is insufficient when LSP traceroute is operated on an LSP with
   Entropy Labels described by [RFC6790].  Therefore, this document
   defines a multipath information type to be used in the DSMAP/DDMAP of
   LSP echo request/reply packets in Section 8.



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   In addition, responder LSR can reply with empty multipath information
   if no IP address set or label set from received multipath information
   matched load balancing to a downstream.  Empty return is also
   possible if initiating LSR sends multipath information of one type,
   IP address or label, but responder LSR load balances on the other
   type.  To disambiguate between the two results, this document
   introduces new flags in the DSMAP/DDMAP TLV to allow responder LSR to
   describe the load balance technique being used.

   It is required that all LSRs along the LSP understand new flags as
   well as new multipath information type.  It is also required that
   initiating LSR can select both IP destination address and label to
   use on transmitting LSP echo request packets.  Two additional DS
   Flags are defined for the DSMAP and DDMAP TLVs in Section 7.

3.  Multipath Type 9

   [RFC4379] defined multipath type {9} for tracing of LSPs where label
   based load-balancing is used.  However, as pointed out in [RFC6790],
   the procedures for using this type are incomplete.  First, the
   specific location of the label was not defined.  What was assumed,
   but not spelled out, was that the presence of multipath type {9}
   meant the responder should act as if the payload of the received
   packet were non-IP and that the bottom-of-stack label should be
   replaced by the values indicated by multipath type {9} to determine
   their respective out-going interfaces.

   Further, with the introduction of [RFC6790], entropy labels may now
   appear anywhere in a label stack.

   This section defines to which labels multipath type {9} can apply.
   Additionally it defines procedures for tracing pseudowires and flow-
   aware pseudowires.  These procedures pertain to the use of multipath
   information type {9} as well as type {10}.

   Section 6 defines a new FEC-Stack sub-TLV to indicate and entropy
   label.  Multipath type {9} applies exclusively to this sub-TLV.  Any
   LSP Ping message containing a DD-MAP or DS-MAP with multipath type
   {9} MUST include an EL_FEC at the bottom of the FEC-Stack.

   When an MPLS echo request message is received containing a FEC-Stack
   with an EL-FEC at the bottom of the FEC stack and is not preceded by
   an entropy label, the responder must behave (for load balancing
   purposes) as if the first word of the message were a Pseudowire
   Control Word.

   In order to trace a non-FAT pseudowire, instead of including the
   appropriate PW-FEC in the FEC-Stack, an EL-FEC is included.  Tracing



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   in this way will cause compliant routers to return the proper
   outgoing interface.  Note that this procedure only traces to the end
   of the MPLS transport LSP (e.g. LDP and/or RSVP).  To actually verify
   the PW-FEC or in the case of a MS-PW, to determine the next
   pseudowire label value, the initiator MUST repeat that step of the
   trace, (i.e., repeating the TTL value used) but with the FEC-Stack
   modified to contain the appropriate PW-FEC.

   In order to trace a FAT pseudowire, the initiator includes an EL-FEC
   at the bottom of the FEC-Stack and pushes the appropriate PW-FEC onto
   the FEC-Stack.

4.  Initiating LSR Procedures

   In order to facilitate the flow of the following text we speak in
   terms of a boolean called EL_LSP maintained by the initiating LSR.
   This value controls the multipath information type to be used in
   transmitted echo request packets.  When the initiating LSR is
   transmitting an echo request packet with DSMAP/DDMAP with a non-zero
   multipath information type, then EL_LSP boolean MUST be consulted to
   determine the multipath information type to use.

   In addition to procedures described in [RFC4379] as updated by
   Section 3 and [RFC6424], initiating LSR MUST operate with following
   procedures.

   o  When initiating LSR is IP based load balancer (not imposing ELI/
      EL), initialize EL_LSP=False.

   o  When initiating LSR imposes ELI/EL, initialize EL_LSP=True.

   o  When initiating LSR is transmitting non-zero multipath information
      type:

         If (EL_LSP) initiating LSR MUST use multipath information type
         {10}.

         Else initiating LSR MUST use multipath information type {2, 4,
         8, 9}.

   o  When initiating LSR is transmitting multipath information type
      {10}, both "IP Multipath Information" and "Label Multipath
      Information" MUST be included, and "IP Associated Label Multipath
      Information" MUST be omitted (NULL).

   o  When initiating LSR receives echo reply with {L=0, E=1} in DS
      flags with valid contents, set EL_LSP=True.




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   In following conditions, initiating LSR may have lost the ability to
   exercise specific ECMP paths.  Initiating LSR MAY continue with "best
   effort".

   o  Received echo reply contains empty multipath information.

   o  Received echo reply contains {L=0, E=<any>} DS flags, but does not
      contain IP multipath information.

   o  Received echo reply contains {L=1, E=<any>} DS flags, but does not
      contain label multipath information.

   o  Received echo reply contains {L=<any>, E=1} DS flags, but does not
      contain associated label multipath information.

   o  IP multipath information types {2, 4, 8} sent, and received echo
      reply with {L=1, E=0} in DS flags.

   o  Multipath information type {10} sent, and received echo reply with
      multipath information type other than {10}.

5.  Responder LSR Procedures

   Common Procedures: Responder LSR receiving LSP echo request packet
   with multipath information type {10} MUST validate following
   contents.  Any deviation MUST result in responder LSR to consider the
   packet as malformed and return code 1 (Malformed echo request
   received) in LSP echo reply packet.

   o  IP multipath information MUST be included.

   o  Label multipath information MUST be included.

   o  IP associated label multipath information MUST be omitted (NULL).

   Following subsections describe expected responder LSR procedures when
   echo reply is to include DSMAP/DDMAP TLVs, based on local load
   balance technique being employed.  In case responder LSR performs
   deviating load balance techniques per downstream basis, appropriate
   procedures matching to each downstream load balance technique MUST be
   operated.

5.1.  IP Based Load Balancer & Not Imposing ELI/EL

   o  Responder MUST set {L=0, E=0} in DS flags.

   o  If multipath information type {2, 4, 8} is received, responder
      MUST comply with [RFC4379]/[RFC6424].



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   o  If multipath information type {9} is received, responder MUST
      reply with multipath type {0}.

   o  If multipath information type {10} is received, responder MUST
      reply with multipath information type {10}. "Label Multipath
      Information" and "Associated Label Multipath Information" sections
      MUST be omitted (NULL).  If no matching IP address is found, then
      "IPMultipathType" field MUST be set to multipath information type
      {0} and "IP Multipath Information" section MUST also be omitted
      (NULL).  If at least one matching IP address is found, then
      "IPMultipathType" field MUST be set to appropriate multipath
      information type {2, 4, 8} and "IP Multipath Information" section
      MUST be included.

5.2.  IP Based Load Balancer & Imposing ELI/EL

   o  Responder MUST set {L=0, E=1} in DS flags.

   o  If multipath information type {9} is received, responder MUST
      reply with multipath type {0}.

   o  If multipath type {2, 4, 8, 10} is received, responder MUST
      respond with multipath type {10}. "Label Multipath Information"
      section MUST be omitted (NULL).  IP address set specified in
      received IP multipath information MUST be used to determine the
      returning IP/Label pairs.  If received multipath information type
      was {10}, received "Label Multipath Information" sections MUST NOT
      be used to determine the associated label portion of returning IP/
      Label pairs.  If no matching IP address is found, then
      "IPMultipathType" field MUST be set to multipath information type
      {0} and "IP Multipath Information" section MUST be omitted (NULL).
      In addition, "Assoc Label Multipath Length" MUST be set to 0, and
      "Associated Label Multipath Information" section MUST also be
      omitted (NULL).  If at least one matching IP address is found,
      then "IPMultipathType" field MUST be set to appropriate multipath
      information type {2, 4, 8} and "IP Multipath Information" section
      MUST be included.  In addition, "Associated Label Multipath
      Information" section MUST be populated with list of labels
      corresponding to each IP address specified in "IP Multipath
      Information" section.  "Assoc Label Multipath Length" MUST be set
      to appropriate value.

5.3.  Label Based Load Balancer & Not Imposing ELI/EL

   o  Responder MUST set {L=1, E=0} in DS flags.

   o  If multipath information type {2, 4, 8} is received, responder
      MUST reply with multipath type {0}.



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   o  If multipath information type {9} is received, responder MUST
      comply with [RFC4379] /[RFC6424] as updated by Section 3.

   o  If multipath information type {10} is received, responder MUST
      reply with multipath information type {10}. "IP Multipath
      Information" and "Associated Label Multipath Information" sections
      MUST be omitted (NULL).  If no matching label is found, then
      "LbMultipathType" field MUST be set to multipath information type
      {0} and "Label Multipath Information" section MUST also be omitted
      (NULL).  If at least one matching label is found, then
      "LbMultipathType" field MUST be set to appropriate multipath
      information type {9} and "Label Multipath Information" section
      MUST be included.

5.4.  Label Based Load Balancer & Imposing ELI/EL

   o  Responder MUST set {L=1, E=1} in DS flags.

   o  If multipath information type {2, 4, 8} is received, responder
      MUST reply with multipath type {0}.

   o  If multipath type {9, 10} is received, responder MUST respond with
      multipath type {10}. "IP Multipath Information" section MUST be
      omitted (NULL).  Label set specified in received label multipath
      information MUST be used to determine the returning Label/Label
      pairs.  If received multipath information type was {10}, received
      "Label Multipath Information" sections MUST NOT be used to
      determine the associated label portion of returning Label/Label
      pairs.  If no matching label is found, then "LbMultipathType"
      field MUST be set to multipath information type {0} and "Label
      Multipath Information" section MUST be omitted (NULL).  In
      addition, "Assoc Label Multipath Length" MUST be set to 0, and
      "Associated Label Multipath Information" section MUST also be
      omitted (NULL).  If at least one matching label is found, then
      "LbMultipathType" field MUST be set to appropriate multipath
      information type {9} and "Label Multipath Information" section
      MUST be included.  In addition, "Associated Label Multipath
      Information" section MUST be populated with list of labels
      corresponding to each label specified in "Label Multipath
      Information" section.  "Assoc Label Multipath Length" MUST be set
      to appropriate value.

5.5.  FAT MS-PW Stitching LSR

   MS-PW stitching LSR that xconnects flow-aware pseudowires behaves in
   one of two ways:





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   o  Load balances on previous flow label, and carries over same flow
      label.  For this case, stitching LSR is to behave as procedures
      described in Section 5.3.

   o  Load balances on previous flow label, and replaces flow label with
      newly computed.  For this case, stitching LSR is to behave as
      procedures described in Section 5.4.

6.  Entropy Label FEC

   Entropy Label Indicator (ELI) is a reserved label that has no
   explicit FEC associated, and has label value 7 assigned from the
   reserved range.  Use Nil FEC as Target FEC Stack sub-TLV to account
   for ELI in a Target FEC Stack TLV.

   Entropy Label (EL) is a special purpose label with label value being
   discretionary (i.e. label value may not be from the reserved range).
   For LSP verification mechanics to perform its purpose, it is
   necessary for a Target FEC Stack sub-TLV to clearly describe EL,
   particularly in the scenario where label stack does not carry ELI
   (ex: FAT-PW [RFC6391]).  Therefore, this document defines a EL FEC to
   allow a Target FEC Stack sub-TLV to be added to the Target FEC Stack
   to account for EL.

   The Length is 4.  Labels are 20-bit values treated as numbers.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Label                 |          MBZ          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Label is the actual label value inserted in the label stack; the MBZ
   fields MUST be zero when sent and ignored on receipt.

7.  DS Flags: L and E

   Two flags, L and E, are added in DS Flags field of the DSMAP/DDMAP
   TLVs.  Both flags MUST NOT be set in echo request packets when
   sending, and ignored when received.  Zero, one or both new flags MUST
   be set in echo reply packets.

    DS Flags
    --------

        0 1 2 3 4 5 6 7
       +-+-+-+-+-+-+-+-+



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       |  MBZ  |L|E|I|N|
       +-+-+-+-+-+-+-+-+


    Flag  Name and Meaning
    ----  ----------------
       L  Label based load balance indicator
          This flag MUST be set to zero in the echo request. LSR
          which performs load balancing on a label MUST set this
          flag in the echo reply. LSR which performs load
          balancing on IP MUST NOT set this flag in the echo
          reply.

       E  ELI/EL imposer indicator
          This flag MUST be set to zero in the echo request. LSR
          which imposes ELI/EL MUST set this flag in the echo
          reply. LSR which does not impose ELI/EL MUST NOT set
          this flag in the echo reply.


   Two flags result in four load balancing techniques which echo reply
   generating LSR can indicate:

   o  {L=0, E=0} LSR load balances based on IP and does not impose ELI/
      EL.

   o  {L=0, E=1} LSR load balances based on IP and imposes ELI/EL.

   o  {L=1, E=0} LSR load balances based on label and does not impose
      ELI/EL.

   o  {L=1, E=1} LSR load balances based on label and imposes ELI/EL.

8.  New Multipath Information Type: 10

   One new multipath information type is added to be used in DSMAP/DDMAP
   TLVs.  New multipath type has value of 10.

   Key   Type                  Multipath Information
   ---   ----------------      ---------------------
    10   IP and label set      IP addresses and label prefixes


   Multipath type 10 is comprised of three sections.  One section to
   describe IP address set.  One section to describe label set.  One
   section to describe another label set which associates to either IP
   address set or label set specified in the other section.




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   Multipath information type 10 has 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |IPMultipathType| Reserved(MBZ) |     IP Multipath Length       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                                                               ~
   |                  (IP Multipath Information)                   |
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |LbMultipathType| Reserved(MBZ) |    Label Multipath Length     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                                                               ~
   |                 (Label Multipath Information)                 |
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Reserved(MBZ)         |  Assoc Label Multipath Length |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                                                               ~
   |            (Associated Label Multipath Information)           |
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   o  IP Multipath Information

         This section reuses IP multipath information from [RFC4379].
         Specifically, values {0, 2, 4, 8} can be used.

   o  Label Multipath Information

         This section reuses label multipath information from [RFC4379].
         Specifically, values {0, 9} can be used.

   o  Associated Label Multipath Information

         "Assoc Label Multipath Length" is a 16 bit field of multipath
         information which indicates length in octets of the associated
         label multipath information.

         "Associated Label Multipath Information" is a list of labels
         with each label described in 24 bits.  This section MUST be
         omitted (NULL) in an MPLS Echo Request message.  A midpoint
         which imposes ELI/EL labels SHOULD include "Assoc Label
         Multipath Information" in its MPLS Echo Reply message, along
         with either "IP Multipath Information" or "Label Multipath
         Information".  Each specified associated label described in



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         this section maps to specific IP address OR label described in
         the "IP Multipath Information" section or "Label Multipath
         Information" section.  For example, if 3 IP addresses are
         specified in the "IP Multipath Information" section, then there
         MUST be 3 labels described in this section.  First label maps
         to the lowest IP address specified, second label maps to the
         second lowest IP address specified and third label maps to the
         third lowest IP address specified.

9.  Unsupported Cases

   There are couple of scenarios where LSP path tracing mechanics are
   not supported in this draft revision.

   o  When one or more LSP transit node(s) performs label based load
      balancing on a label that is not bottom-of-stack label when
      Entropy Label Indicator is not included.

   o  When one or more LSP transit node(s) performs label based load
      balancing on a label other than Entropy Label when Entropy Label
      Indicator and Entropy Label pair is included.

10.  Security Considerations

   Beyond those specified in [RFC4379], [RFC6424] and [RFC6790], there
   are no further security measured required.

11.  IANA Considerations

11.1.  DS Flags

   DS flags ... not maintained by IANA.  Should it be?

11.2.  Multipath Information Types

   Multipath information types ... not maintained by IANA.  Should it
   be?

11.3.  Entropy Label FEC

   IANA is requested to assign a new sub-TLV from the "Sub-TLVs for TLV
   Types 1 and 16" section from "TLVs" sub-registry within the "Multi-
   Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping
   Parameters" registry.

   Following value appears to be next available sub-TLV value.
   Requesting IANA to allow specified value as early allocation.




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   Value   Meaning                            Reference
   -----   -------                            ---------
      26   Entropy Label FEC                  this document


12.  Acknowledgements

   TBD

13.  Contributing Authors

   Nagendra Kumar
   Cisco Systems
   Email: naikumar@cisco.com

14.  References

14.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol
              Label Switched (MPLS) Data Plane Failures", RFC 4379,
              February 2006.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, November 2012.

14.2.  Informative References

   [I-D.ravisingh-mpls-el-for-seamless-mpls]
              Singh, R., Shen, Y., and J. Drake, "Entropy label for
              seamless MPLS", draft-ravisingh-mpls-el-for-seamless-
              mpls-00 (work in progress), February 2013.

   [RFC6391]  Bryant, S., Filsfils, C., Drafz, U., Kompella, V., Regan,
              J., and S. Amante, "Flow-Aware Transport of Pseudowires
              over an MPLS Packet Switched Network", RFC 6391, November
              2011.

   [RFC6424]  Bahadur, N., Kompella, K., and G. Swallow, "Mechanism for
              Performing Label Switched Path Ping (LSP Ping) over MPLS
              Tunnels", RFC 6424, November 2011.

Authors' Addresses




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   Nobo Akiya
   Cisco Systems

   Email: nobo@cisco.com


   George Swallow
   Cisco Systems

   Email: swallow@cisco.com


   Carlos Pignataro
   Cisco Systems

   Email: cpignata@cisco.com



































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