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Versions: 00 01 02 03 04 05 draft-ietf-mpls-lsp-ping-lag-multipath

Internet Engineering Task Force                                 N. Akiya
Internet-Draft                                                G. Swallow
Updates: 4379,6424 (if approved)                           Cisco Systems
Intended status: Standards Track                            S. Litkowski
Expires: June 24, 2015                                       B. Decraene
                                                                  Orange
                                                                J. Drake
                                                        Juniper Networks
                                                       December 21, 2014


       Label Switched Path (LSP) Ping/Trace Multipath Support for
                Link Aggregation Group (LAG) Interfaces
               draft-akiya-mpls-lsp-ping-lag-multipath-05

Abstract

   This document defines an extension to the MPLS Label Switched Path
   (LSP) Ping and Traceroute as specified in RFC 4379.  The extension
   allows the MPLS LSP Ping and Traceroute to discover and exercise
   specific paths of Layer 2 (L2) Equal-Cost Multipath (ECMP) over Link
   Aggregation Group (LAG) interfaces.

   This document updates RFC4379 and RFC6424.

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 June 24, 2015.




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Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Background  . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  LSR Capability Discovery  . . . . . . . . . . . . . . . . . .   6
   4.  Mechanism to Discover L2 ECMP Multipath . . . . . . . . . . .   7
     4.1.  Initiator LSR Procedures  . . . . . . . . . . . . . . . .   7
     4.2.  Responder LSR Procedures  . . . . . . . . . . . . . . . .   7
     4.3.  Additional Initiator LSR Procedures . . . . . . . . . . .   9
   5.  Mechanism to Validate L2 ECMP Traversal . . . . . . . . . . .  10
     5.1.  Incoming LAG Member Links Verification  . . . . . . . . .  11
       5.1.1.  Initiator LSR Procedures  . . . . . . . . . . . . . .  11
       5.1.2.  Responder LSR Procedures  . . . . . . . . . . . . . .  11
       5.1.3.  Additional Initiator LSR Procedures . . . . . . . . .  12
     5.2.  Individual End-to-End Path Verification . . . . . . . . .  13
   6.  LSR Capability TLV  . . . . . . . . . . . . . . . . . . . . .  14
   7.  LAG Description Indicator Flag: G . . . . . . . . . . . . . .  15
   8.  Local Interface Index Sub-TLV . . . . . . . . . . . . . . . .  16
   9.  Remote Interface Index Sub-TLV  . . . . . . . . . . . . . . .  17
   10. Detailed Interface and Label Stack TLV  . . . . . . . . . . .  18
     10.1.  Sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . .  20
       10.1.1.  Incoming Label Stack Sub-TLV . . . . . . . . . . . .  20
       10.1.2.  Incoming Interface Index Sub-TLV . . . . . . . . . .  20
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  21
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
     12.1.  LSR Capability TLV . . . . . . . . . . . . . . . . . . .  22
       12.1.1.  LSR Capability Flags . . . . . . . . . . . . . . . .  22
     12.2.  Local Interface Index Sub-TLV  . . . . . . . . . . . . .  22
       12.2.1.  Interface Index Flags  . . . . . . . . . . . . . . .  23
     12.3.  Remote Interface Index Sub-TLV . . . . . . . . . . . . .  23
     12.4.  Detailed Interface and Label Stack TLV . . . . . . . . .  23



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       12.4.1.  Sub-TLVs for TLV Type TBD4 . . . . . . . . . . . . .  24
     12.5.  DS Flags . . . . . . . . . . . . . . . . . . . . . . . .  24
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  24
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  25
     14.2.  Informative References . . . . . . . . . . . . . . . . .  25
   Appendix A.  LAG with L2 Switch Issues  . . . . . . . . . . . . .  26
     A.1.  Equal Numbers of LAG Members  . . . . . . . . . . . . . .  26
     A.2.  Deviating Numbers of LAG Members  . . . . . . . . . . . .  26
     A.3.  LAG Only on Right . . . . . . . . . . . . . . . . . . . .  26
     A.4.  LAG Only on Left  . . . . . . . . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Introduction

1.1.  Terminology

   The following acronyms/terms are used in this document:

   o  MPLS - Multiprotocol Label Switching.

   o  LSP - Label Switched Path.

   o  LSR - Label Switching Router.

   o  ECMP - Equal-Cost Multipath.

   o  LAG - Link Aggregation Group.

   o  Initiator LSR - LSR which sends MPLS echo request.

   o  Responder LSR - LSR which receives MPLS echo request and sends
      MPLS echo reply.

1.2.  Background

   The MPLS Label Switched Path (LSP) Ping and Traceroute as specified
   in [RFC4379] are powerful tools designed to diagnose all available
   layer 3 (L3) paths of LSPs, i.e., provides diagnostic coverage of L3
   Equal-Cost Multipath (ECMP).  In many MPLS networks, Link Aggregation
   Group (LAG) as defined in [IEEE802.1AX], which provide Layer 2 (L2)
   ECMP, are often used for various reasons.  MPLS LSP Ping and
   Traceroute tools were not designed to discover and exercise specific
   paths of L2 ECMP.  The result raises a limitation for following
   scenario when LSP X traverses over LAG Y:

   o  Label switching of LSP X over one or more member links of LAG Y
      have succeeded.



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   o  Label switching of LSP X over one or more member links of LAG Y
      have failed.

   o  MPLS echo request for LSP X over LAG Y is load balanced over a
      member link which is label switching successfully.

   With the above scenario, MPLS LSP Ping and Traceroute will not be
   able to detect the label switching failure of problematic member
   link(s) of the LAG.  In other words, lack of L2 ECMP diagnostic
   coverage can produce an outcome where MPLS LSP Ping and Traceroute
   can be blind to label switching failures over problematic LAG
   interface.  It is, thus, desirable to extend the MPLS LSP Ping and
   Traceroute to have deterministic diagnostic coverage of LAG
   interfaces.

   Creation of this document was motivated by issues encountered in live
   networks.

2.  Overview

   This document defines an extension to the MPLS LSP Ping and
   Traceroute to describe Multipath Information for LAG member links
   separately, thus allowing MPLS LSP Ping and Traceroute to discover
   and exercise specific paths of L2 ECMP over LAG interfaces.  Reader
   is expected to be familiar with mechanics of the MPLS LSP Ping and
   Traceroute described in Section 3.3 of [RFC4379] and Downstream
   Detailed Mapping TLV (DDMAP) described in Section 3.3 of [RFC6424].

   MPLS echo request carries a DDMAP and an optional TLV to indicate
   that separate load balancing information for each L2 nexthop over LAG
   is desired in MPLS echo reply.  Responder LSR places the same
   optional TLV in the MPLS echo reply to provide acknowledgement back
   to the initiator.  It also adds, for each downstream LAG member, a
   load balance information (i.e. multipath information and interface
   index).  The following figure and the texts provides an example using
   an LDP network.  However the problem and the mechanism is applicable
   to all types of LSPs which can traverse over LAG interfaces.














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     <----- LDP Network ----->

             +-------+
             |       |
     A-------B=======C-------E
             |               |
             +-------D-------+

     ---- Non-LAG
     ==== LAG comprising of two member links

         Figure 1: Example LDP Network

   When node A is initiating LSP Traceroute to node E, node B will
   return to node A load balance information for following entries.

   1.  Downstream C over Non-LAG (upper path).

   2.  First Downstream C over LAG (middle path).

   3.  Second Downstream C over LAG (middle path).

   4.  Downstream D over Non-LAG (lower path).

   This document defines:

   o  In Section 3, a mechanism discover capabilities of responder LSRs;

   o  In Section 4, a mechanism to discover L2 ECMP multipath
      information;

   o  In Section 5, a mechanism to validate L2 ECMP traversal in some
      LAG provisioning models;

   o  In Section 6, the LSR Capability TLV;

   o  In Section 7, the LAG Description Indicator flag;

   o  In Section 8, the Local Interface Index Sub-TLV;

   o  In Section 9, the Remote Interface Index Sub-TLV;

   o  In Section 10, the Detailed Interface and Label Stack TLV;

   o  In Appendix A, issues with LAG having an L2 Switch.

   Note that the mechanism described in this document does not impose
   any changes to scenarios where an LSP is pinned down to a particular



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   LAG member (i.e. the LAG is not treated as one logical interface by
   the LSP).

   Also note that many LAGs are built from p2p links, and thus router X
   and router X+1 have the same number of LAG members.  It is possible
   to build LAGs asymmetrically by using Ethernet switches in the
   middle.  Appendix A lists some cases which this document does not
   address; if an operator deploys LAGs in a manner similar to what's
   shown in Appendix A, the mechanisms in this document may not suit
   them.

3.  LSR Capability Discovery

   The MPLS Ping operates by an initiator LSR sending an MPLS echo
   request message and receiving back a corresponding MPLS echo reply
   message from a responder LSR.  The MPLS Traceroute operates in a
   similar way except the initiator LSR potentially sends multiple MPLS
   echo request messages with incrementing TTL values.

   There has been many extensions to the MPLS Ping and Traceroute
   mechanism over the years.  Thus it is often useful, and sometimes
   necessary, for the initiator LSR to deterministically disambiguate
   the difference between:

   o  The responder LSR sent the MPLS echo reply message with contents C
      because it has feature X, Y and Z implemented.

   o  The responder LSR sent the MPLS echo reply message with contents C
      because it has subset of features X, Y and Z implemented but not
      all.

   o  The responder LSR sent the MPLS echo reply message with contents C
      because it does not have features X, Y and Z implemented.

   To allow the initiator LSR to disambiguate the above differences,
   this document defines the LSR Capability TLV (described in
   Section 6).  When the initiator LSR wishes to discover the
   capabilities of the responder LSR, the initiator LSR includes the LSR
   Capability TLV in the MPLS echo request message.  When the responder
   LSR receives an MPLS echo reply message with the LSR Capability TLV
   included, then the responder LSR MUST include the LSR Capability TLV
   in the MPLS echo reply message with the LSR Capability TLV describing
   features and extensions supported by the local LSR.

   It is RECOMMENDED that implementations supporting the LAG Multipath
   extensions defined in this document include the LSR Capability TLV in
   MPLS echo request messages.




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4.  Mechanism to Discover L2 ECMP Multipath

4.1.  Initiator LSR Procedures

   The MPLS echo request carries a DDMAP with the "LAG Description
   Indicator flag" (G) set in the DS Flags to indicate that separate
   load balancing information for each L2 nexthop over LAG is desired in
   MPLS echo reply.  The new "LAG Description Indicator flag" is
   described in Section 7.

4.2.  Responder LSR Procedures

   This section describes the handling of the new TLVs by nodes which
   understand the "LAG Description Indicator flag".  There are two cases
   - nodes which understand the "LAG Description Indicator flag" but
   which for some reason cannot describe LAG members separately, and
   nodes which both understand the "LAG Description Indicator flag" and
   are able to describe LAG members separately.  Note that Section 6,
   Section 8 and Section 9 describe the new TLVs referenced by this
   section , and looking over the definition of the new TLVs first may
   make it easier to read this section.

   A responder LSR that understand the "LAG Description Indicator flag"
   but is not capable of describing outgoing LAG member links separately
   uses the following procedures:

   o  If the received MPLS echo request message had the LSR Capability
      TLV, the responder LSR MUST include the LSR Capability TLV in the
      MPLS echo reply message.

   o  The responder LSR MUST clear the "Downstream LAG Info
      Accommodation flag" in the LSR Capability Flags field of the LSR
      Capability TLV.  This will allow the initiator LSR to understand
      that the responder LSR cannot describe outgoing LAG member links
      separately in the DDMAP.

   A responder LSR that understands the "LAG Description Indicator flag"
   and is capable of describing outgoing LAG member links separately
   uses the follow procedures, regardless of whether or not outgoing
   interfaces include LAG interfaces:

   o  If the received MPLS echo request message had the LSR Capability
      TLV, the responder LSR MUST include the LSR Capability TLV in the
      MPLS echo reply message.

   o  The responder LSR MUST set the "Downstream LAG Info Accommodation
      flag" in the LSR Capability Flags field of the LSR Capability TLV.




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   o  For each downstream that is a LAG interface:

      *  The responder LSR MUST add DDMAP in the MPLS echo reply.

      *  The responder LSR MUST set the "LAG Description Indicator flag"
         in the DS Flags field of the DDMAP.

      *  In the DDMAP, Local Interface Index Sub-TLV, Remote Interface
         Index Sub-TLV and Multipath Data Sub-TLV are to describe each
         LAG member link.  All other fields of the DDMAP are to describe
         the LAG interface.

      *  For each LAG member link of this LAG interface:

         +  The responder LSR MUST add a Local Interface Index Sub-TLV
            (described in Section 8) with the "LAG Member Link Indicator
            flag" set in the Interface Index Flags field, describing the
            interface index of this outgoing LAG member link (the local
            interface index is assigned by the local LSR).

         +  The responder LSR MAY add a Remote Interface Index Sub-TLV
            (described in Section 9) with the "LAG Member Link Indicator
            flag" set in the Interface Index Flags field, describing the
            interface index of the incoming LAG member link on the
            downstream LSR (this interface index is assigned by the
            downstream LSR).  How the local LSR obtains the interface
            index of the LAG member link on the downstream LSR is
            outside the scope of this document.

         +  The responder LSR MUST add an Multipath Data Sub-TLV for
            this LAG member link, if received DDMAP requested multipath
            information.

   Based on the procedures described above, every LAG member link will
   have a Local Interface Index Sub-TLV and a Multipath Data Sub-TLV
   entries in the DDMAP.  The order of the Sub-TLVs in the DDMAP for a
   LAG member link MUST be Local Interface Index Sub-TLV immediately
   followed by Multipath Data Sub-TLV.  A LAG member link may also have
   a corresponding Remote Interface Index Sub-TLV.  When a Local
   Interface Index Sub-TLV, a Remote Interface Index-Sub-TLV and a
   Multipath Data Sub-TLV are placed in the DDMAP to describe a LAG
   member link, they MUST be placed in the order of Local Interface
   Index Sub-TLV, Remote Interface Index-Sub-TLV and Multipath Data Sub-
   TLV.

   A responder LSR possessing a LAG interface with two member links
   would send the following DDMAP for this LAG interface:




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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~   DDMAP fields describing LAG interface with DS Flags G set   ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |[MANDATORY] Local Interface Index Sub-TLV of LAG member link #1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |[OPTIONAL] Remote Interface Index Sub-TLV of LAG member link #1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |[MANDATORY] Multipath Data Sub-TLV LAG member link #1          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |[MANDATORY] Local Interface Index Sub-TLV of LAG member link #2|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |[OPTIONAL] Remote Interface Index Sub-TLV of LAG member link #2|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |[MANDATORY] Multipath Data Sub-TLV LAG member link #2          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Label Stack Sub-TLV                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 2: Example of DDMAP in MPLS Echo Reply

   When none of the received multipath information maps to a particular
   LAG member link, then the responder LSR MUST still place the Local
   Interface Index Sub-TLV and the Multipath Data Sub-TLV for that LAG
   member link in the DDMAP, with the Multipath Length field of the
   Multipath Data Sub-TLV being zero.

4.3.  Additional Initiator LSR Procedures

   The procedures above allow an initiator LSR to:

   o  Identify whether or not the responder LSR can describe outgoing
      LAG member links separately, by looking at the LSR Capability TLV.

   o  Utilize the value of the "LAG Description Indicator flag" in DS
      Flags to identify whether each received DDMAP describes a LAG
      interface or a non-LAG interface.

   o  Obtain multipath information which is expected to traverse the
      specific LAG member link described by corresponding interface
      index.

   When an initiator LSR receives a DDMAP containing LAG member
   information from a downstream LSR with TTL=n, then the subsequent
   DDMAP sent by the initiator LSR to the downstream LSR with TTL=n+1
   through a particular LAG member link MUST be updated with following
   procedures:



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   o  The Local Interface Index Sub-TLVs MUST be removed in the sending
      DDMAP.

   o  If the Remote Interface Index Sub-TLVs were present and the
      initiator LSR is traversing over a specific LAG member link, then
      the Remote Interface Index Sub-TLV corresponding to the LAG member
      link being traversed SHOULD be included in the sending DDMAP.  All
      other Remote Interface Index Sub-TLVs MUST be removed from the
      sending DDMAP.

   o  The Multipath Data Sub-TLVs MUST be updated to include just one
      Multipath Data Sub-TLV.  The initiator MAY keep just the Multipath
      Data Sub-TLV corresponding to the LAG member link being traversed,
      or combine the Multipath Data Sub-TLVs for all LAG member links
      into a single Multipath Data Sub-TLV when diagnosing further
      downstream LSRs.

   o  All other fields of the DDMAP are to comply with procedures
      described in [RFC6424].

   Using the DDMAP example described in the Figure 2, the DDMAP being
   sent by the initiator LSR through LAG member link #1 to the next
   downstream LSR should be:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~   DDMAP fields describing LAG interface with DS Flags G set   ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |[OPTIONAL] Remote Interface Index Sub-TLV of LAG member link #1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Multipath Data Sub-TLV LAG member link #1         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Label Stack Sub-TLV                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 3: Example of DDMAP in MPLS Echo Request

5.  Mechanism to Validate L2 ECMP Traversal

   Section 4 defines the responder LSR procedures to constructs a DDMAP
   for a downstream LAG, and also defines that inclusion of the Remote
   Interface Index Sub-TLVs describing the incoming LAG member links of
   the downstream LSR is optional.  The reason why it is optional for
   the responder LSR to include the Remote Interface Index Sub-TLVs is
   that this information from the downstream LSR is often not available
   on the responder LSR.  In such case, the traversal of LAG member
   links can be validated with procedures described in Section 5.1.  If



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   LSRs can provide the Remote Interface Index Sub-TLVs in DDMAP
   objects, then the validation procedures described in Section 5.2 can
   be used.

5.1.  Incoming LAG Member Links Verification

   Without downstream LSRs returning remote Interface Index Sub-TLVs in
   the DDMAP, validation of the LAG member link traversal requires that
   initiator LSR traverses all available LAG member links and taking the
   results through a logic.  This section provides the mechanism for the
   initiator LSR to obtain additional information from the downstream
   LSRs and describes the additional logic in the initiator LSR to
   validate the L2 ECMP traversal.

5.1.1.  Initiator LSR Procedures

   The MPLS echo request is sent with a DDMAP with the "Interface and
   Label Stack Object Request flag" and "LAG Description Indicator flag"
   set in the DS Flags to indicate the request for Detailed Interface
   and Label Stack TLV with additional LAG member link information (i.e.
   interface index) in the MPLS echo reply.

5.1.2.  Responder LSR Procedures

   A responder LSR that understands the "LAG Description Indicator flag"
   but is not capable of describing incoming LAG member link is to use
   following procedures:

   o  If the received MPLS echo request message had the LSR Capability
      TLV, the responder LSR MUST include the LSR Capability TLV in the
      MPLS echo reply message.

   o  The responder LSR MUST clear the "Upstream LAG Info Accommodation
      flag" in the LSR Capability Flags field of the LSR Capability TLV.
      This will allow the initiator LSR to understand that the responder
      LSR cannot describe incoming LAG member link.

   A responder LSR that understands the "LAG Description Indicator flag"
   and is capable of describing incoming LAG member link MUST use the
   following procedures, regardless of whether or not incoming interface
   was a LAG interface:

   o  If the received MPLS echo request message had the LSR Capability
      TLV, the responder LSR MUST include the LSR Capability TLV in the
      MPLS echo reply message.

   o  The responder LSR MUST set the "Upstream LAG Info Accommodation
      flag" in the LSR Capability Flags field of the LSR Capability TLV.



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   o  When the received DDMAP had "Interface and Label Stack Object
      Request flag" set in the DS Flags field, the responder LSR MUST
      add the Detailed Interface and Label Stack TLV (described in
      Section 10) in the MPLS echo reply.

   o  When the received DDMAP had "Interface and Label Stack Object
      Request flag" set in the DS Flags field and the incoming interface
      was a LAG, the responder LSR MUST add the Incoming Interface Index
      Sub-TLV (described in Section 10.1.2) in the Detailed Interface
      and Label Stack TLV.  The "LAG Member Link Indicator flag" MUST be
      set in the Interface Index Flags field, and the Interface Index
      field set to the LAG member link which received the MPLS echo
      request.

   These procedures allow initiator LSR to:

   o  Identify whether or not the responder LSR can describe the
      incoming LAG member link, by looking at the LSR Capability TLV.

   o  Utilize the Incoming Interface Index Sub-TLV in the Detailed
      Interface and Label Stack TLV to identify, if the incoming
      interface was a LAG, the identity of the incoming LAG member.

5.1.3.  Additional Initiator LSR Procedures

   Along with procedures described in Section 4, the procedures
   described in this section will allow an initiator LSR to know:

   o  The expected load balance information of every LAG member link, at
      LSR with TTL=n.

   o  With specific entropy, the expected interface index of the
      outgoing LAG member link at TTL=n.

   o  With specific entropy, the interface index of the incoming LAG
      member link at TTL=n+1.

   Expectation is that there's a relationship between the interface
   index of the outgoing LAG member link at TTL=n and the interface
   index of the incoming LAG member link at TTL=n+1 for all discovered
   entropies.  In other words, set of entropies that load balances to
   outgoing LAG member link X at TTL=n should all reach the nexthop on
   same incoming LAG member link Y at TTL=n+1.

   With additional logics, the initiator LSR can perform following
   checks in a scenario where the initiator knows that there is a LAG,
   with two LAG members, between TTL=n and TTL=n+1, and has the
   multipath information to traverse the two LAG members.



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   The initiator LSR sends two MPLS echo request messages to traverse
   the two LAG members at TTL=1:

   o  Success case:

      *  One MPLS echo request message reaches TTL=n+1 on an LAG member
         1.

      *  The other MPLS echo request message reaches TTL=n+1 on an LAG
         member 2.

      The two MPLS echo request messages sent by the initiator LSR reach
      two different LAG members at the immediate downstream LSR.

   o  Error case:

      *  One MPLS echo request message reaches TTL=n+1 on an LAG member
         1.

      *  The other MPLS echo request message also reaches TTL=n+1 on an
         LAG member 1.

      One or two MPLS echo request messages sent by the initiator LSR
      does not reach the immediate downstream LSR, or the two MPLS echo
      request messages reach a same LAG member at the immediate
      downstream LSR.

   Note that defined procedures will provide a deterministic result for
   LAG interfaces that are back-to-back connected between routers (i.e.
   no L2 switch in between).  If there is a L2 switch between LSR at
   TTL=n and LSR at TTL=n+1, there is no guarantee that traversal of
   every LAG member link at TTL=n will result in reaching different
   interface index at TTL=n+1.  Issues resulting from LAG with L2 switch
   in between are further described in Appendix A.  LAG provisioning
   models in operated network should be considered when analyzing the
   output of LSP Traceroute exercising L2 ECMPs.

5.2.  Individual End-to-End Path Verification

   When the Remote Interface Index Sub-TLVs are available from an LSR
   with TTL=n, then the validation of LAG member link traversal can be
   performed by the downstream LSR of TTL=n+1.  The initiator LSR
   follows the procedures described in Section 4.3.

   The DDMAP validation procedures by the downstream responder LSR are
   then updated to include the comparison of the incoming LAG member
   link (which MPLS echo request was received on) to the interface index
   described in the Remote Interface Index Sub-TLV in the DDMAP.



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   Failure of this comparison results in the return code being set to
   "Downstream Mapping Mismatch (5)".

   A responder LSR that is not able to perform the above additional
   DDMAP validation procedures is considered to lack the upstream LAG
   capability.  Thus, if the received MPLS echo request contained the
   LSR Capability TLV, then the responder LSR MUST include the LSR
   Capability TLV in the MPLS echo reply and the LSR Capability TLV MUST
   have the "Upstream LAG Info Accomodation flag" cleared.

6.  LSR Capability TLV

   The LSR Capability object is a new TLV that MAY be included in the
   MPLS echo request message and the MPLS echo reply message.  An MPLS
   echo request message and an MPLS echo reply message MUST NOT include
   more than one LSR Capability object.  Presence of an LSR Capability
   object in an MPLS echo request message is a request that a responder
   LSR includes an LSR Capability object in the MPLS echo reply message,
   with the LSR Capability object describing features and extensions
   supported.  When the received MPLS echo request message contains an
   LSR Capability object, an responder LSR MUST include the LSR
   Capability object in the MPLS echo reply message.

   LSR Capability TLV Type is TBD1.  Length is 4.  The value field of
   the LSR Capability TLV 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Type              |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      LSR Capability Flags                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 4: LSR Capability TLV

   LSR Capability Flags

      The LSR Capability Flags field is a bit vector with 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Must Be Zero (Reserved)                  |U|D|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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      Two flags are defined: U and D.  The remaining flags MUST be set
      to zero when sending and ignored on receipt.  Both U and D flags
      MUST be cleared in MPLS echo request message when sending, and
      ignored on receipt.  Neither, either or both U and D flags MAY be
      set in MPLS echo reply message.

      Flag  Name and Meaning
      ----  ----------------

         U  Upstream LAG Info Accommodation

            An LSR sets this flag when the node is capable of
            describing a LAG member link in the Incoming Interface
            Index Sub-TLV in the in the Detailed Interface and
            Label Stack TLV.

         D  Downstream LAG Info Accommodation

            An LSR sets this flag when the node is capable of
            describing LAG member links in the Local Interface
            Index Sub-TLV and the Multipath Data Sub-TLV in the
            Downstream Detailed Mapping TLV.

7.  LAG Description Indicator Flag: G

   One flag, G, is added in DS Flags field of the DDMAP TLV.  The G flag
   of the DS Flags field in the MPLS echo request message indicates the
   request for detailed LAG information from the responder LSR.  In the
   MPLS echo reply message, the G flag MUST be set if the DDMAP TLV
   describes a LAG interface.  It MUST be cleared otherwise.

   DS Flags

      DS Flags G is added, in Bit Number TBD5, in DS Flags bit vector.

       0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+
      | MBZ |G|MBZ|I|N|
      +-+-+-+-+-+-+-+-+

      RFC-Editor-Note: Please update above figure to place the flag G in
      the bit number TBD5.









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     Flag  Name and Meaning
     ----  ----------------

        G  LAG Description Indicator

           When this flag is set in the MPLS echo request, responder is
           requested to respond with detailed LAG information. When this
           flag is set in the MPLS echo reply, the corresponding DDMAP
           describes a LAG interface.

8.  Local Interface Index Sub-TLV

   The Local Interface Index object is a Sub-TLV that MAY be included in
   a DDMAP TLV.  Zero or more Local Interface Index object MAY appear in
   a DDMAP TLV.  The Local Interface Index Sub-TLV describes the index
   assigned by the local LSR to the egress interface.

   The Local Interface Index Sub-TLV Type is TBD2.  Length is 8, and the
   Value field 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Type              |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Interface Index Flags      |         Must Be Zero          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Local Interface Index                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 5: Local Interface Index Sub-TLV

   Interface Index Flags

      Interface Index Flags field is a bit vector with following format.

      0                   1
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Must Be Zero (Reserved)   |M|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      One flag is defined: M.  The remaining flags MUST be set to zero
      when sending and ignored on receipt.







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     Flag  Name and Meaning
     ----  ----------------

        M  LAG Member Link Indicator

           When this flag is set, interface index described in
           this sub-TLV is a member of a LAG.


   Local Interface Index

      An Index assigned by the LSR to this interface.

9.  Remote Interface Index Sub-TLV

   The Remote Interface Index object is a Sub-TLV that MAY be included
   in a DDMAP TLV.  Zero or more Remote Interface Index object MAY
   appear in a DDMAP TLV.  The Remote Interface Index Sub-TLV describes
   the index assigned by the downstream LSR to the ingress interface.

   The Remote Interface Index Sub-TLV Type is TBD3.  Length is 8, and
   the Value field 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Type              |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Interface Index Flags      |         Must Be Zero          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Remote Interface Index                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 6: Remote Interface Index Sub-TLV

   Interface Index Flags

      Interface Index Flags field is a bit vector with following format.

      0                   1
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Must Be Zero (Reserved)   |M|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      One flag is defined: M.  The remaining flags MUST be set to zero
      when sending and ignored on receipt.




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     Flag  Name and Meaning
     ----  ----------------

        M  LAG Member Link Indicator

           When this flag is set, interface index described in
           this sub-TLV is a member of a LAG.


   Remote Interface Index

      An Index assigned by the downstream LSR to the ingress interface.

10.  Detailed Interface and Label Stack TLV

   The "Detailed Interface and Label Stack" object is a TLV that MAY be
   included in a MPLS echo reply message to report the interface on
   which the MPLS echo request message was received and the label stack
   that was on the packet when it was received.  A responder LSR MUST
   NOT insert more than one instance of this TLV.  This TLV allows the
   initiator LSR to obtain the exact interface and label stack
   information as it appears at the responder LSR.

   Detailed Interface and Label Stack TLV Type is TBD4.  Length is K +
   Sub-TLV Length (sum of Sub-TLVs).  K is the sum of all fields of this
   TLV prior to Sub-TLVs, but the length of K depends on the Address
   Type.  Details of this information is described below.  The Value
   field 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Type              |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Address Type  |             Must Be Zero                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   IP Address (4 or 16 octets)                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Interface (4 or 16 octets)                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Must Be Zero         |        Sub-TLV Length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     .                                                               .
     .                      List of Sub-TLVs                         .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 7: Detailed Interface and Label Stack TLV



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   The Detailed Interface and Label Stack TLV format is derived from the
   Interface and Label Stack TLV format (from [RFC4379]).  Two changes
   are introduced.  First is that label stack, which is of variable
   length, is converted into a sub-TLV.  Second is that a new sub-TLV is
   added to describe an interface index.  The fields of Detailed
   Interface and Label Stack TLV have the same use and meaning as in
   [RFC4379].  A summary of the fields taken from the Interface and
   Label Stack TLV is as below:

      Address Type

         The Address Type indicates if the interface is numbered or
         unnumbered.  It also determines the length of the IP Address
         and Interface fields.  The resulting total for the initial part
         of the TLV is listed in the table below as "K Octets".  The
         Address Type is set to one of the following values:

            Type #        Address Type           K Octets
            ------        ------------           --------
                 1        IPv4 Numbered                16
                 2        IPv4 Unnumbered              16
                 3        IPv6 Numbered                40
                 4        IPv6 Unnumbered              28

      IP Address and Interface

         IPv4 addresses and interface indices are encoded in 4 octets;
         IPv6 addresses are encoded in 16 octets.

         If the interface upon which the echo request message was
         received is numbered, then the Address Type MUST be set to IPv4
         Numbered or IPv6 Numbered, the IP Address MUST be set to either
         the LSR's Router ID or the interface address, and the Interface
         MUST be set to the interface address.

         If the interface is unnumbered, the Address Type MUST be either
         IPv4 Unnumbered or IPv6 Unnumbered, the IP Address MUST be the
         LSR's Router ID, and the Interface MUST be set to the index
         assigned to the interface.

         Note: Usage of IPv6 Unnumbered has the same issue as [RFC4379],
         described in Section 3.4.2 of [I-D.ietf-mpls-ipv6-only-gap].  A
         solution should be considered an applied to both [RFC4379] and
         this document.

      Sub-TLV Length





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         Total length in octets of the sub-TLVs associated with this
         TLV.

10.1.  Sub-TLVs

   This section defines the sub-TLVs that MAY be included as part of the
   Detailed Interface and Label Stack TLV.

           Sub-Type    Value Field
           ---------   ------------
             1         Incoming Label stack
             2         Incoming Interface Index

10.1.1.  Incoming Label Stack Sub-TLV

   The Incoming Label Stack sub-TLV contains the label stack as received
   by the LSR.  If any TTL values have been changed by this LSR, they
   SHOULD be restored.

   Incoming Label Stack Sub-TLV Type is 1.  Length is variable, and the
   Value field 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Type              |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 Label                 | TC  |S|      TTL      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     .                                                               .
     .                                                               .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 Label                 | TC  |S|      TTL      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 8: Incoming Label Stack Sub-TLV

10.1.2.  Incoming Interface Index Sub-TLV

   The Incoming Interface Index object is a Sub-TLV that MAY be included
   in a Detailed Interface and Label Stack TLV.  The Incoming Interface
   Index Sub-TLV describes the index assigned by this LSR to the
   interface which received the MPLS echo request message.

   Incoming Interface Index Sub-TLV Type is 2.  Length is 8, and the
   Value field has the same format as the Local Interface Index Sub-TLV
   described in Section 8, and has 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Type              |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Interface Index Flags      |         Must Be Zero          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Incoming Interface Index                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 9: Incoming Interface Index Sub-TLV

   Interface Index Flags

      Interface Index Flags field is a bit vector with following format.

      0                   1
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Must Be Zero (Reserved)   |M|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      One flag is defined: M.  The remaining flags MUST be set to zero
      when sending and ignored on receipt.

     Flag  Name and Meaning
     ----  ----------------

        M  LAG Member Link Indicator

           When this flag is set, interface index described in
           this sub-TLV is a member of a LAG.


   Incoming Interface Index

      An Index assigned by the LSR to this interface.

11.  Security Considerations

   This document extends LSP Traceroute mechanism to discover and
   exercise L2 ECMP paths.  As a result of supporting the code points
   and procedures described in this document, additional processing are
   required by initiator LSRs and responder LSRs, especially to compute
   and handle increasing number of multipath information.  Due to
   additional processing, it is critical that proper security measures
   described in [RFC4379] and [RFC6424] are followed.




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   The LSP Traceroute allows an initiator LSR to discover the paths of
   tested LSPs, providing deep knowledge of the MPLS network.  Exposing
   such information to a malicious user is considered dangerous.  To
   prevent leakage of vital information to untrusted users, a responder
   LSR MUST only accept MPLS echo request messages from trusted sources
   via filtering source IP address field of received MPLS echo request
   messages.

12.  IANA Considerations

12.1.  LSR Capability TLV

   The IANA is requested to assign new value TBD1 for LSR Capability TLV
   from the "Multiprotocol Label Switching Architecture (MPLS) Label
   Switched Paths (LSPs) Ping Parameters - TLVs" registry.

     Value   Meaning                                      Reference
     -----   -------                                      ---------
     TBD1    LSR Capability TLV                           this document

12.1.1.  LSR Capability Flags

   The IANA is requested to create and maintain a registry entitled "LSR
   Capability Flags" with following registration procedures:

    Registry Name: LAG Interface Info Flags

    Bit number Name                                        Reference
    ---------- ----------------------------------------    ---------
            31 D: Downstream LAG Info Accommodation        this document
            30 U: Upstream LAG Info Accommodation          this document
          0-29 Unassigned

   Assignments of LSR Capability Flags are via Standards Action
   [RFC5226].

12.2.  Local Interface Index Sub-TLV

   The IANA is requested to assign new value TBD2 (from the range
   4-31743) for the Local Interface Index Sub-TLV from the
   "Multiprotocol Label Switching Architecture (MPLS) Label Switched
   Paths (LSPs) Ping Parameters - TLVs" registry, "Sub-TLVs for TLV
   Types 20" sub-registry.

     Value   Meaning                                      Reference
     -----   -------                                      ---------
     TBD2    Local Interface Index Sub-TLV                this document




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12.2.1.  Interface Index Flags

   The IANA is requested to create and maintain a registry entitled
   "Interface Index Flags" with following registration procedures:

    Registry Name: Interface Index Flags

    Bit number Name                                        Reference
    ---------- ----------------------------------------    ---------
            15 M: LAG Member Link Indicator                this document
          0-14 Unassigned

   Assignments of Interface Index Flags are via Standards Action
   [RFC5226].

   Note that this registry is used by the Interface Index Flags field of
   following Sub-TLVs:

   o  The Local Interface Index Sub-TLV which may be present in the
      "Downstream Detailed Mapping" TLV.

   o  The Remote Interface Index Sub-TLV which may be present in the
      "Downstream Detailed Mapping" TLV.

   o  The Incoming Interface Index Sub-TLV which may be present in the
      "Detailed Interface and Label Stack" TLV.

12.3.  Remote Interface Index Sub-TLV

   The IANA is requested to assign new value TBD3 (from the range
   32768-49161) for the Remote Interface Index Sub-TLV from the
   "Multiprotocol Label Switching Architecture (MPLS) Label Switched
   Paths (LSPs) Ping Parameters - TLVs" registry, "Sub-TLVs for TLV
   Types 20" sub-registry.

     Value   Meaning                                      Reference
     -----   -------                                      ---------
     TBD3    Remote Interface Index Sub-TLV               this document

12.4.  Detailed Interface and Label Stack TLV

   The IANA is requested to assign new value TBD4 for Detailed Interface
   and Label Stack TLV from the "Multiprotocol Label Switching
   Architecture (MPLS) Label Switched Paths (LSPs) Ping Parameters -
   TLVs" registry ([IANA-MPLS-LSP-PING]).






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     Value   Meaning                                      Reference
     -----   -------                                      ---------
     TBD4    Detailed Interface and Label Stack TLV       this document

12.4.1.  Sub-TLVs for TLV Type TBD4

   The IANA is requested to create and maintain a sub-registry entitled
   "Sub-TLVs for TLV Type TBD4" under "Multiprotocol Label Switching
   Architecture (MPLS) Label Switched Paths (LSPs) Ping Parameters -
   TLVs" registry.

   Initial values for this sub-registry, "Sub-TLVs for TLV Types TBD4",
   are described below.

     Sub-Type     Name                                    Reference
     -----------  --------------------------------------  ---------
     1            Incoming Label Stack                    this document
     2            Incoming Interface Index                this document
     3-16383      Unassigned (mandatory TLVs)
     16384-31743  Experimental
     32768-49161  Unassigned (optional TLVs)
     49162-64511  Experimental

   Assignments of Sub-Types in the mandatory and optional spaces are are
   via Standards Action [RFC5226].  Assignments of Sub-Types in the
   experimental space is via Specification Required [RFC5226].

12.5.  DS Flags

   The IANA is requested to assign a new bit number from the "DS flags"
   sub-registry from the "Multi-Protocol Label Switching (MPLS) Label
   Switched Paths (LSPs) Ping Parameters - TLVs" registry
   ([IANA-MPLS-LSP-PING]).

   Note: the "DS flags" sub-registry is created by
   [I-D.ietf-mpls-lsp-ping-registry].

    Bit number Name                                        Reference
    ---------- ----------------------------------------    ---------
          TBD5 G: LAG Description Indicator                this document

13.  Acknowledgements

   The authors would like to thank Nagendra Kumar and Sam Aldrin for
   providing useful comments and suggestions.  The authors would like to
   thank Loa Andersson for performing a detailed review and providing
   number of comments.




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   The authors also would like to extend sincere thanks to the MPLS RT
   review members who took time to review and provide comments.  The
   members are Eric Osborne, Mach Chen and Yimin Shen.  The suggestion
   by Mach Chen to generalize and create the LSR Capability TLV was
   tremendously helpful for this document and likely for future
   documents extending the MPLS LSP Ping and Traceroute mechanism.  The
   suggestion by Yimin Shen to create two separate validation procedures
   had a big impact to the contents of this document.

14.  References

14.1.  Normative References

   [I-D.ietf-mpls-lsp-ping-registry]
              Decraene, B., Akiya, N., Pignataro, C., Andersson, L., and
              S. Aldrin, "IANA registries for LSP ping Code Points",
              draft-ietf-mpls-lsp-ping-registry-00 (work in progress),
              November 2014.

   [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.

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

14.2.  Informative References

   [I-D.ietf-mpls-ipv6-only-gap]
              George, W. and C. Pignataro, "Gap Analysis for Operating
              IPv6-only MPLS Networks", draft-ietf-mpls-ipv6-only-gap-04
              (work in progress), November 2014.

   [IANA-MPLS-LSP-PING]
              IANA, "Multi-Protocol Label Switching (MPLS) Label
              Switched Paths (LSPs) Ping Parameters",
              <http://www.iana.org/assignments/mpls-lsp-ping-parameters/
              mpls-lsp-ping-parameters.xhtml>.

   [IEEE802.1AX]
              IEEE Std. 802.1AX, "IEEE Standard for Local and
              metropolitan area networks - Link Aggregation", November
              2008.




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   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

Appendix A.  LAG with L2 Switch Issues

   Several flavors of "LAG with L2 switch" provisioning models are
   described in this section, with MPLS data plane ECMP traversal
   validation issues with each.

A.1.  Equal Numbers of LAG Members

   R1 ==== S1 ==== R2

   The issue with this LAG provisioning model is that packets traversing
   a LAG member from R1 to S1 can get load balanced by S1 towards R2.
   Therefore, MPLS echo request messages traversing specific LAG member
   from R1 to S1 can actually reach R2 via any LAG members, and sender
   of MPLS echo request messages have no knowledge of this nor no way to
   control this traversal.  In the worst case, MPLS echo request
   messages with specific entropies to exercise every LAG members from
   R1 to S1 can all reach R2 via same LAG member.  Thus it is impossible
   for MPLS echo request sender to verify that packets intended to
   traverse specific LAG member from R1 to S1 did actually traverse that
   LAG member, and to deterministically exercise "receive" processing of
   every LAG member on R2.

A.2.  Deviating Numbers of LAG Members

              ____
   R1 ==== S1 ==== R2

   There are deviating number of LAG members on the two sides of the L2
   switch.  The issue with this LAG provisioning model is the same as
   previous model, sender of MPLS echo request messages have no
   knowledge of L2 load balance algorithm nor entropy values to control
   the traversal.

A.3.  LAG Only on Right

   R1 ---- S1 ==== R2

   The issue with this LAG provisioning model is that there is no way
   for MPLS echo request sender to deterministically exercise both LAG
   members from S1 to R2.  And without such, "receive" processing of R2
   on each LAG member cannot be verified.





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A.4.  LAG Only on Left

   R1 ==== S1 ---- R2

   MPLS echo request sender has knowledge of how to traverse both LAG
   members from R1 to S1.  However, both types of packets will terminate
   on the non-LAG interface at R2.  It becomes impossible for MPLS echo
   request sender to know that MPLS echo request messages intended to
   traverse a specific LAG member from R1 to S1 did indeed traverse that
   LAG member.

Authors' Addresses

   Nobo Akiya
   Cisco Systems

   Email: nobo@cisco.com


   George Swallow
   Cisco Systems

   Email: swallow@cisco.com


   Stephane Litkowski
   Orange

   Email: stephane.litkowski@orange.com


   Bruno Decraene
   Orange

   Email: bruno.decraene@orange.com


   John E. Drake
   Juniper Networks

   Email: jdrake@juniper.net










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