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rfc:rfc8611

Internet Engineering Task Force (IETF) N. Akiya Request for Comments: 8611 Big Switch Networks Updates: 8029 G. Swallow Category: Standards Track SETC ISSN: 2070-1721 S. Litkowski

                                                           B. Decraene
                                                                Orange
                                                              J. Drake
                                                      Juniper Networks
                                                               M. Chen
                                                                Huawei
                                                             June 2019
  Label Switched Path (LSP) Ping and Traceroute Multipath Support
            for Link Aggregation Group (LAG) Interfaces

Abstract

 This document defines extensions to the MPLS Label Switched Path
 (LSP) Ping and Traceroute mechanisms as specified in RFC 8029.  The
 extensions allow the MPLS LSP Ping and Traceroute mechanisms to
 discover and exercise specific paths of Layer 2 (L2) Equal-Cost
 Multipath (ECMP) over Link Aggregation Group (LAG) interfaces.
 Additionally, a mechanism is defined to enable the determination of
 the capabilities supported by a Label Switching Router (LSR).
 This document updates RFC 8029.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8611.

Akiya, et al. Standards Track [Page 1] RFC 8611 LSP Ping for LAG June 2019

Copyright Notice

 Copyright (c) 2019 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
 (https://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.  Background  . . . . . . . . . . . . . . . . . . . . . . .   3
   1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   1.3.  Requirements Language . . . . . . . . . . . . . . . . . .   4
 2.  Overview of Solution  . . . . . . . . . . . . . . . . . . . .   4
 3.  LSR Capability Discovery  . . . . . . . . . . . . . . . . . .   6
   3.1.  Initiator LSR Procedures  . . . . . . . . . . . . . . . .   7
   3.2.  Responder LSR Procedures  . . . . . . . . . . . . . . . .   7
 4.  Mechanism to Discover L2 ECMP . . . . . . . . . . . . . . . .   7
   4.1.  Initiator LSR Procedures  . . . . . . . . . . . . . . . .   7
   4.2.  Responder LSR Procedures  . . . . . . . . . . . . . . . .   8
   4.3.  Additional Initiator LSR Procedures . . . . . . . . . . .  10
 5.  Mechanism to Validate L2 ECMP Traversal . . . . . . . . . . .  11
   5.1.  Incoming LAG Member Links Verification  . . . . . . . . .  11
     5.1.1.  Initiator LSR Procedures  . . . . . . . . . . . . . .  11
     5.1.2.  Responder LSR Procedures  . . . . . . . . . . . . . .  12
     5.1.3.  Additional Initiator LSR Procedures . . . . . . . . .  12
   5.2.  Individual End-to-End Path Verification . . . . . . . . .  14
 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  . . . . . . . . . . .  17
   10.1.  Sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . .  19
     10.1.1.  Incoming Label Stack Sub-TLV . . . . . . . . . . . .  19
     10.1.2.  Incoming Interface Index Sub-TLV . . . . . . . . . .  20
 11. Rate-Limiting on Echo Request/Reply Messages  . . . . . . . .  21
 12. Security Considerations . . . . . . . . . . . . . . . . . . .  21
 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
   13.1.  LSR Capability TLV . . . . . . . . . . . . . . . . . . .  22
     13.1.1.  LSR Capability Flags . . . . . . . . . . . . . . . .  22

Akiya, et al. Standards Track [Page 2] RFC 8611 LSP Ping for LAG June 2019

   13.2.  Local Interface Index Sub-TLV  . . . . . . . . . . . . .  22
     13.2.1.  Interface Index Flags  . . . . . . . . . . . . . . .  22
   13.3.  Remote Interface Index Sub-TLV . . . . . . . . . . . . .  23
   13.4.  Detailed Interface and Label Stack TLV . . . . . . . . .  23
     13.4.1.  Sub-TLVs for TLV Type 6  . . . . . . . . . . . . . .  23
     13.4.2.  Interface and Label Stack Address Types  . . . . . .  25
   13.5.  DS Flags . . . . . . . . . . . . . . . . . . . . . . . .  25
 14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
   14.1.  Normative References . . . . . . . . . . . . . . . . . .  25
   14.2.  Informative References . . . . . . . . . . . . . . . . .  26
 Appendix A.  LAG with Intermediate L2 Switch Issues . . . . . . .  27
   A.1.  Equal Numbers of LAG Members  . . . . . . . . . . . . . .  27
   A.2.  Deviating Numbers of LAG Members  . . . . . . . . . . . .  27
   A.3.  LAG Only on Right . . . . . . . . . . . . . . . . . . . .  27
   A.4.  LAG Only on Left  . . . . . . . . . . . . . . . . . . . .  28
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  28
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1. Introduction

1.1. Background

 The MPLS Label Switched Path (LSP) Ping and Traceroute mechanisms
 [RFC8029] are powerful tools designed to diagnose all available
 Layer 3 (L3) paths of LSPs, including diagnostic coverage of L3
 Equal-Cost Multipath (ECMP).  In many MPLS networks, Link Aggregation
 Groups (LAGs), as defined in [IEEE802.1AX], provide Layer 2 (L2) ECMP
 and are often used for various reasons.  MPLS LSP Ping and Traceroute
 tools were not designed to discover and exercise specific paths of L2
 ECMP.  This produces a limitation for the following scenario when an
 LSP traverses a LAG:
 o  Label switching over some member links of the LAG is successful,
    but fails over other member links of the LAG.
 o  MPLS echo request for the LSP over the LAG is load-balanced on one
    of the member links that is label switching successfully.
 With the above scenario, MPLS LSP Ping and Traceroute will not be
 able to detect the label-switching failure of the 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 a problematic LAG
 interface.  It is, thus, desirable to extend the MPLS LSP Ping and
 Traceroute to have deterministic diagnostic coverage of LAG
 interfaces.

Akiya, et al. Standards Track [Page 3] RFC 8611 LSP Ping for LAG June 2019

 The work toward a solution to this problem was motivated by issues
 encountered in live networks.

1.2. 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 - The LSR that sends the MPLS echo request message.
 o  Responder LSR - The LSR that receives the MPLS echo request
    message and sends the MPLS echo reply message.

1.3. Requirements Language

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

2. Overview of Solution

 This document defines a new TLV to discover the capabilities of a
 responder LSR and extensions for use with the MPLS LSP Ping and
 Traceroute mechanisms to describe Multipath Information for
 individual LAG member links, thus allowing MPLS LSP Ping and
 Traceroute to discover and exercise specific paths of L2 ECMP over
 LAG interfaces.  The reader is expected to be familiar with the
 Downstream Detailed Mapping TLV (DDMAP) described in Section 3.4 of
 [RFC8029].
 The solution consists of the MPLS echo request containing a DDMAP TLV
 and the new LSR Capability TLV to indicate that separate load-
 balancing information for each L2 next hop over LAG is desired in the
 MPLS echo reply.  The responder LSR places the same LSR Capability
 TLV in the MPLS echo reply to provide acknowledgement back to the
 initiator LSR.  It also adds, for each downstream LAG member, load-
 balancing information (i.e., multipath information and interface

Akiya, et al. Standards Track [Page 4] RFC 8611 LSP Ping for LAG June 2019

 index).  This mechanism is applicable to all types of LSPs that can
 traverse LAG interfaces.  Many LAGs are built from peer-to-peer
 links, with router X and router X+1 having direct connectivity and
 the same number of LAG members.  It is possible to build LAGs
 asymmetrically by using Ethernet switches between two routers.
 Appendix A lists some use cases for which the mechanisms defined in
 this document may not be applicable.  Note that the mechanisms
 described in this document do not impose any changes to scenarios
 where an LSP is pinned down to a particular LAG member (i.e., the LAG
 is not treated as one logical interface by the LSP).
 The following figure and description provide an example of an LDP
 network.
   <----- LDP Network ----->
           +-------+
           |       |
   A-------B=======C-------E
           |               |
           +-------D-------+
  1. — 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-balancing information for the 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 to discover capabilities of responder
    LSRs;
 o  in Section 4, a mechanism to discover L2 ECMP information;
 o  in Section 5, a mechanism to validate L2 ECMP traversal;

Akiya, et al. Standards Track [Page 5] RFC 8611 LSP Ping for LAG June 2019

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

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 have been many extensions to the MPLS Ping and Traceroute
 mechanisms over the years.  Thus, it is often useful, and sometimes
 necessary, for the initiator LSR to deterministically disambiguate
 the differences 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 a subset of features X, Y, and Z (i.e., not all of
    them) implemented.
 o  The responder LSR sent the MPLS echo reply message with contents C
    because it does not have features X, Y, or 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 request message with the LSR Capability TLV
 included, if it knows the LSR Capability TLV, then it MUST include
 the LSR Capability TLV in the MPLS echo reply message with the LSR
 Capability TLV describing the features and extensions supported by
 the local LSR.  Otherwise, an MPLS echo reply must be sent back to
 the initiator LSR with the return code set to "One or more of the
 TLVs was not understood", according to the rules defined in Section 3
 of [RFC8029].  Then, the initiator LSR can send another MPLS echo
 request without including the LSR Capability TLV.

Akiya, et al. Standards Track [Page 6] RFC 8611 LSP Ping for LAG June 2019

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

3.1. Initiator LSR Procedures

 If an initiator LSR does not know what capabilities a responder LSR
 can support, it can send an MPLS echo request message and carry the
 LSR Capability TLV to the responder to discover the capabilities that
 the responder LSR can support.

3.2. Responder LSR Procedures

 When a responder LSR receives an MPLS echo request message that
 carries the LSR Capability TLV, the following procedures are used:
 If the responder knows how to process the LSR Capability TLV, the
 following procedures are used:
 o  The responder LSR MUST include the LSR Capability TLV in the MPLS
    echo reply message.
 o  If the responder LSR understands the LAG Description Indicator
    flag:
  • Set the Downstream LAG Info Accommodation flag if the responder

LSR is capable of describing the outgoing LAG member links

       separately; otherwise, clear the Downstream LAG Info
       Accommodation flag.
  • Set the Upstream LAG Info Accommodation flag if the responder

LSR is capable of describing the incoming LAG member links

       separately; otherwise, clear the Upstream LAG Info
       Accommodation flag.

4. Mechanism to Discover L2 ECMP

4.1. Initiator LSR Procedures

 Through LSR Capability Discovery as defined in Section 3, the
 initiator LSR can understand whether the responder LSR can describe
 incoming/outgoing LAG member links separately in the DDMAP TLV.
 Once the initiator LSR knows that a responder can support this
 mechanism, then it sends an MPLS echo request carrying a DDMAP TLV
 with the LAG Description Indicator flag (G) set to the responder LSR.
 The LAG Description Indicator flag (G) indicates that separate load-

Akiya, et al. Standards Track [Page 7] RFC 8611 LSP Ping for LAG June 2019

 balancing information for each L2 next hop over a LAG is desired in
 the MPLS echo reply.  The new LAG Description Indicator flag is
 described in Section 7.

4.2. Responder LSR Procedures

 When a responder LSR receives an MPLS echo request message with the
 LAG Description Indicator flag set in the DDMAP TLV, if the responder
 LSR understands the LAG Description Indicator flag and is capable of
 describing outgoing LAG member links separately, the following
 procedures are used, regardless of whether or not the outgoing
 interfaces include LAG interfaces:
 o  For each downstream interface that is a LAG interface:
  • The responder LSR MUST include a DDMAP TLV when sending the

MPLS echo reply. There is a single DDMAP TLV for the LAG

       interface, with member links described using sub-TLVs.
  • The responder LSR MUST set the LAG Description Indicator flag

in the DS Flags field of the DDMAP TLV.

  • In the DDMAP TLV, the Local Interface Index Sub-TLV, Remote

Interface Index Sub-TLV, and Multipath Data Sub-TLV are used to

       describe each LAG member link.  All other fields of the DDMAP
       TLV are used to describe the LAG interface.
  • For each LAG member link of the 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.  It describes
          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.  It describes
          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 a Multipath Data Sub-TLV for this
          LAG member link, if the received DDMAP TLV requested
          multipath information.

Akiya, et al. Standards Track [Page 8] RFC 8611 LSP Ping for LAG June 2019

 Based on the procedures described above, every LAG member link will
 have a Local Interface Index Sub-TLV and a Multipath Data Sub-TLV
 entry in the DDMAP TLV.  The order of the sub-TLVs in the DDMAP TLV
 for a LAG member link MUST be Local Interface Index Sub-TLV
 immediately followed by Multipath Data Sub-TLV, except as follows.  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
 TLV 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.  The blocks of Local Interface Index, Remote
 Interface Index (optional), and Multipath Data Sub-TLVs for each
 member link MUST appear adjacent to each other and be in order of
 increasing local interface index.
 A responder LSR possessing a LAG interface with two member links
 would send the following DDMAP for this LAG interface:
    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 (DS Flags with G set)  ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Local Interface Index Sub-TLV of LAG member link #1           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Remote Interface Index Sub-TLV of LAG member link #1          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Multipath Data Sub-TLV LAG member link #1                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Local Interface Index Sub-TLV of LAG member link #2           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Remote Interface Index Sub-TLV of LAG member link #2          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 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 TLV.  The value of the Multipath Length
 field of the Multipath Data Sub-TLV is set to zero.

Akiya, et al. Standards Track [Page 9] RFC 8611 LSP Ping for LAG June 2019

4.3. Additional Initiator LSR Procedures

 The procedures in Section 4.2 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 TLV describes a LAG
    interface or a non-LAG interface.
 o  Obtain multipath information that is expected to traverse the
    specific LAG member link described by the 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 according to the
 following procedures:
 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 LSR MAY just keep 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 [RFC8029].

Akiya, et al. Standards Track [Page 10] RFC 8611 LSP Ping for LAG June 2019

 Figure 3 is an example that shows how to use the DDMAP TLV to send a
 notification about which member link (link #1 in the example) will be
 chosen to send the MPLS echo request message to the next downstream
 LSR:
    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 (DS Flags with 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 construct a DDMAP
 for a downstream LAG.  The Remote Interface Index Sub-TLV that
 describes the incoming LAG member links of the downstream LSR is
 optional, because 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 LSRs can provide the Remote Interface Index Sub-
 TLVs, 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
 the initiator LSR traverses all available LAG member links and takes
 the results through additional 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

 An MPLS echo request carrying a DDMAP TLV with the Interface and
 Label Stack Object Request flag and LAG Description Indicator flag
 set is sent 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.

Akiya, et al. Standards Track [Page 11] RFC 8611 LSP Ping for LAG June 2019

5.1.2. Responder LSR Procedures

 When it receives an echo request with the LAG Description Indicator
 flag set, a responder LSR that understands that flag and is capable
 of describing the incoming LAG member link SHOULD use the following
 procedures, regardless of whether or not the incoming interface was a
 LAG interface:
 o  When the I flag (Interface and Label Stack Object Request flag) of
    the DDMAP TLV in the received MPLS echo request is set:
  • The responder LSR MUST add the Detailed Interface and Label

Stack TLV (described in Section 10) in the MPLS echo reply.

  • If the incoming interface is 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 that received the MPLS echo request.
 These procedures allow the initiator LSR to utilize the Incoming
 Interface Index Sub-TLV in the Detailed Interface and the Label Stack
 TLV to derive, if the incoming interface is 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.
 Depending on the LAG traffic division algorithm, the messages may or
 may not traverse different member links.  The 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 entropies examined.  In other words,
 the messages with a set of entropies that load-balances to outgoing
 LAG member link X at TTL=n should all reach the next hop on the same
 incoming LAG member link Y at TTL=n+1.

Akiya, et al. Standards Track [Page 12] RFC 8611 LSP Ping for LAG June 2019

 With additional logic, the initiator LSR can perform the following
 checks in a scenario where it (a) knows that there is a LAG that has
 two LAG members, between TTL=n and TTL=n+1, and (b) has the multipath
 information to traverse the two LAG member links.
 The initiator LSR sends two MPLS echo request messages to traverse
 the two LAG member links at TTL=n+1:
 o  Success case:
  • One MPLS echo request message reaches TTL=n+1 on LAG member

link 1.

  • The other MPLS echo request message reaches TTL=n+1 on LAG

member link 2.

    The two MPLS echo request messages sent by the initiator LSR reach
    the immediate downstream LSR from two different LAG member links.
 o  Error case:
  • One MPLS echo request message reaches TTL=n+1 on LAG member

link 1.

  • The other MPLS echo request message also reaches TTL=n+1 on LAG

member link 1.

  • One or both MPLS echo request messages cannot reach the

immediate downstream LSR on whichever link.

    One or two MPLS echo request messages sent by the initiator LSR
    cannot reach the immediate downstream LSR, or the two MPLS echo
    request messages reach at the immediate downstream LSR from the
    same LAG member link.
 Note that the procedures defined above will provide a deterministic
 result for LAG interfaces that are back-to-back connected between
 LSRs (i.e., no L2 switch in between).  If there is an L2 switch
 between the LSR at TTL=n and the LSR at TTL=n+1, there is no
 guarantee that every incoming interface at TTL=n+1 can be traversed,
 even when traversing every outgoing LAG member link at TTL=n.  Issues
 resulting from LAG with an L2 switch in between are further described
 in Appendix A.  LAG provisioning models in operator networks should
 be considered when analyzing the output of LSP Traceroute that is
 exercising L2 ECMPs.

Akiya, et al. Standards Track [Page 13] RFC 8611 LSP Ping for LAG June 2019

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 for the downstream responder LSR are
 then updated to include the comparison of the incoming LAG member
 link to the interface index described in the Remote Interface Index
 Sub-TLV in the DDMAP TLV.  Failure of this comparison results in the
 return code being set to "Downstream Mapping Mismatch (5)".

6. LSR Capability TLV

 This document defines a new TLV that is referred to as the LSR
 Capability TLV.  It 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
 TLV.  The presence of an LSR Capability TLV in an MPLS echo request
 message is a request that a responder LSR includes an LSR Capability
 TLV in the MPLS echo reply message, with the LSR Capability TLV
 describing features and extensions that the responder LSR supports.
 The format of the LSR Capability TLV is as below:
 LSR Capability TLV Type is 4.  Length is 4.  The LSR Capability TLV
 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      LSR Capability Flags                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     Figure 4: LSR Capability TLV
 Where:
    The Type field is 2 octets in length, and the value is 4.
    The Length field is 2 octets in length, and the value is 4.

Akiya, et al. Standards Track [Page 14] RFC 8611 LSP Ping for LAG June 2019

    The LSR Capability Flags field is 4 octets in length; this
    document defines the following flags:
    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Reserved (Must Be Zero)                   |U|D|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    This document defines two flags.  The unallocated flags MUST be
    set to zero when sending and ignored on receipt.  Both the U and
    the D flag MUST be cleared in the MPLS echo request message when
    sending and ignored on receipt.  Zero, one, or both of the flags
    (U and D) MAY be set in the MPLS echo reply message.
    Flag  Name and Meaning
    ----  ----------------
       U  Upstream LAG Info Accommodation
          An LSR sets this flag when the LSR is capable of describing
          a LAG member link in the Incoming Interface Index Sub-TLV
          in the Detailed Interface and Label Stack TLV.
       D  Downstream LAG Info Accommodation
          An LSR sets this flag when the LSR 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

 This document defines a new flag, the G flag (LAG Description
 Indicator), in the DS Flags field of the DDMAP TLV.
 The G flag 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.

Akiya, et al. Standards Track [Page 15] RFC 8611 LSP Ping for LAG June 2019

 The G flag is defined as below:
    The Bit Number is 3.
     0 1 2 3 4 5 6 7
    +-+-+-+-+-+-+-+-+
    | MBZ |G|E|L|I|N|
    +-+-+-+-+-+-+-+-+
 Flag  Name and Meaning
 ----  ----------------
    G  LAG Description Indicator
       When this flag is set in the MPLS echo request, the responder
       LSR is requested to respond with detailed LAG information.
       When this flag is set in the MPLS echo reply, the corresponding
       DDMAP TLV describes a LAG interface.

8. Local Interface Index Sub-TLV

 The Local Interface Index Sub-TLV describes the interface index
 assigned by the local LSR to an egress interface.  One or more Local
 Interface Index sub-TLVs MAY appear in a DDMAP TLV.
 The format of the Local Interface Index Sub-TLV is below:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Local Interface Index                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 5: Local Interface Index Sub-TLV
 Where:
 o  The Type field is 2 octets in length, and the value is 4.
 o  The Length field is 2 octets in length, and the value is 4.
 o  The Local Interface Index field is 4 octets in length; it is an
    interface index assigned by a local LSR to an egress interface.
    It's normally an unsigned integer and in network byte order.

Akiya, et al. Standards Track [Page 16] RFC 8611 LSP Ping for LAG June 2019

9. Remote Interface Index Sub-TLV

 The Remote Interface Index Sub-TLV is an optional TLV; it describes
 the interface index assigned by a downstream LSR to an ingress
 interface.  One or more Remote Interface Index sub-TLVs MAY appear in
 a DDMAP TLV.
 The format of the Remote Interface Index Sub-TLV is below:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Remote Interface Index                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 6: Remote Interface Index Sub-TLV
 Where:
 o  The Type field is 2 octets in length, and the value is 5.
 o  The Length field is 2 octets in length, and the value is 4.
 o  The Remote Interface Index field is 4 octets in length; it is an
    interface index assigned by a downstream LSR to an ingress
    interface.  It's normally an unsigned integer and in network byte
    order.

10. Detailed Interface and Label Stack TLV

 The Detailed Interface and Label Stack TLV MAY be included in an 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 into the MPLS echo reply message.  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 6.  Length is K + Sub-
 TLV Length (sum of Sub-TLVs).  K is the sum of all fields of this TLV
 prior to the list of Sub-TLVs, but the length of K depends on the
 Address Type.  Details of this information is described below.  The
 Detailed Interface and Label Stack TLV has the following format:

Akiya, et al. Standards Track [Page 17] RFC 8611 LSP Ping for LAG June 2019

    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  |             Reserved (Must Be Zero)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   IP Address (4 or 16 octets)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Interface (4 or 16 octets)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                      List of Sub-TLVs                         .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           Figure 7: Detailed Interface and Label Stack TLV
 The Detailed Interface and Label Stack TLV format is derived from the
 Interface and Label Stack TLV format (from [RFC8029]).  Two changes
 are introduced.  The first is that the label stack is converted into
 a sub-TLV.  The second is that a new sub-TLV is added to describe an
 interface index.  The other fields of the Detailed Interface and
 Label Stack TLV have the same use and meaning as in [RFC8029].  A
 summary of these fields 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 length of the
       initial part of the TLV is listed 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

Akiya, et al. Standards Track [Page 18] RFC 8611 LSP Ping for LAG June 2019

       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 [RFC8029],
       which is described in Section 3.4.2 of [RFC7439].  A solution
       should be considered and applied to both [RFC8029] and this
       document.

10.1. Sub-TLVs

 This section defines the sub-TLVs that MAY be included as part of the
 Detailed Interface and Label Stack TLV.  Two sub-TLVs are defined:
         Sub-Type    Sub-TLV Name
         ---------   ------------
           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 an 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 its
 format is as below:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Label                 | TC  |S|      TTL      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                                                               .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Label                 | TC  |S|      TTL      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 8: Incoming Label Stack Sub-TLV

Akiya, et al. Standards Track [Page 19] RFC 8611 LSP Ping for LAG June 2019

10.1.2. Incoming Interface Index Sub-TLV

 The Incoming Interface Index Sub-TLV MAY be included in a Detailed
 Interface and Label Stack TLV.  The Incoming Interface Index Sub-TLV
 describes the index assigned by a local LSR to the interface that
 received the MPLS echo request message.
 Incoming Interface Index Sub-TLV Type is 2.  Length is 8, and its
 format is as below:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Interface Index Flags      |       Reserved (Must Be Zero) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Incoming Interface Index                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 9: Incoming Interface Index Sub-TLV
 Interface Index Flags
    The 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Reserved (Must Be Zero)   |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, the 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.  It's normally an
    unsigned integer and in network byte order.

Akiya, et al. Standards Track [Page 20] RFC 8611 LSP Ping for LAG June 2019

11. Rate-Limiting on Echo Request/Reply Messages

 An LSP may be over several LAGs.  Each LAG may have many member
 links.  To exercise all the links, many echo request/reply messages
 will be sent in a short period.  It's possible that those messages
 may traverse a common path as a burst.  Under some circumstances,
 this might cause congestion at the common path.  To avoid potential
 congestion, it is RECOMMENDED that implementations randomly delay the
 echo request and reply messages at the initiator LSRs and responder
 LSRs.  Rate-limiting of ping traffic is further specified in
 Section 5 of [RFC8029] and Section 4.1 of [RFC6425], which apply to
 this document as well.

12. Security Considerations

 This document extends the LSP Traceroute mechanism [RFC8029] to
 discover and exercise L2 ECMP paths to determine problematic member
 link(s) of a LAG.  These on-demand diagnostic mechanisms are used by
 an operator within an MPLS control domain.
 [RFC8029] reviews the possible attacks and approaches to mitigate
 possible threats when using these mechanisms.
 To prevent leakage of vital information to untrusted users, a
 responder LSR MUST only accept MPLS echo request messages from
 designated trusted sources via filtering the source IP address field
 of received MPLS echo request messages.  As noted in [RFC8029],
 spoofing attacks only have a small window of opportunity.  If an
 intermediate node hijacks these messages (i.e., causes non-delivery),
 the use of these mechanisms will determine the data plane is not
 working as it should.  Hijacking of a responder node such that it
 provides a legitimate reply would involve compromising the node
 itself and the MPLS control domain.  [RFC5920] provides additional
 MPLS network-wide operation recommendations to avoid attacks.  Please
 note that source IP address filtering provides only a weak form of
 access control and is not, in general, a reliable security mechanism.
 Nonetheless, it is required here in the absence of any more robust
 mechanisms that might be used.

Akiya, et al. Standards Track [Page 21] RFC 8611 LSP Ping for LAG June 2019

13. IANA Considerations

13.1. LSR Capability TLV

 IANA has assigned value 4 (from the range 0-16383) for the LSR
 Capability TLV from the "TLVs" registry under the "Multiprotocol
 Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
 registry [IANA-MPLS-LSP-PING].
   Type    TLV Name                                    Reference
   -----   --------                                    ---------
     4     LSR Capability                              RFC 8611

13.1.1. LSR Capability Flags

 IANA has created a new "LSR Capability Flags" registry.  The initial
 contents are as follows:
   Value   Meaning                                     Reference
   -----   -------                                     ---------
     31    D: Downstream LAG Info Accommodation        RFC 8611
     30    U: Upstream LAG Info Accommodation          RFC 8611
   0-29    Unassigned
 Assignments of LSR Capability Flags are via Standards Action
 [RFC8126].

13.2. Local Interface Index Sub-TLV

 IANA has assigned value 4 (from the range 0-16383) for the Local
 Interface Index Sub-TLV from the "Sub-TLVs for TLV Type 20"
 subregistry of the "TLVs" registry in the "Multiprotocol Label
 Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
 registry [IANA-MPLS-LSP-PING].
   Sub-Type   Sub-TLV Name                             Reference
   --------   ------------                             ---------
      4       Local Interface Index                    RFC 8611

13.2.1. Interface Index Flags

 IANA has created a new "Interface Index Flags" registry.  The initial
 contents are as follows:
  Bit Number Name                                      Reference
  ---------- --------------------------------          ---------
       15    M: LAG Member Link Indicator              RFC 8611
     0-14    Unassigned

Akiya, et al. Standards Track [Page 22] RFC 8611 LSP Ping for LAG June 2019

 Assignments of Interface Index Flags are via Standards Action
 [RFC8126].
 Note that this registry is used by the Interface Index Flags field of
 the 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.

13.3. Remote Interface Index Sub-TLV

 IANA has assigned value 5 (from the range 0-16383) for the Remote
 Interface Index Sub-TLV from the "Sub-TLVs for TLV Type 20"
 subregistry of the "TLVs" registry in the "Multiprotocol Label
 Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
 registry [IANA-MPLS-LSP-PING].
   Sub-Type   Sub-TLV Name                             Reference
   --------   ------------                             ---------
     5        Remote Interface Index                   RFC 8611

13.4. Detailed Interface and Label Stack TLV

 IANA has assigned value 6 (from the range 0-16383) for the Detailed
 Interface and Label Stack TLV from the "TLVs" registry in the
 "Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs)
 Ping Parameters" registry [IANA-MPLS-LSP-PING].
   Type    TLV Name                                    Reference
   -----   --------                                    ---------
     6     Detailed Interface and Label Stack          RFC 8611

13.4.1. Sub-TLVs for TLV Type 6

 RFC 8029 changed the registration procedures for TLV and sub-TLV
 registries for LSP Ping.
 IANA has created a new "Sub-TLVs for TLV Type 6" subregistry under
 the "TLVs" registry of the "Multiprotocol Label Switching (MPLS)
 Label Switched Paths (LSPs) Ping Parameters" registry
 [IANA-MPLS-LSP-PING].

Akiya, et al. Standards Track [Page 23] RFC 8611 LSP Ping for LAG June 2019

 This registry conforms with RFC 8029.
 The registration procedures for this sub-TLV registry are:
 Range        Registration Procedure   Note
 -----        ----------------------   -----
 0-16383      Standards Action         This range is for mandatory
                                       TLVs or for optional TLVs that
                                       require an error message if
                                       not recognized.
 16384-31743  RFC Required             This range is for mandatory
                                       TLVs or for optional TLVs that
                                       require an error message if
                                       not recognized.
 31744-32767  Private Use              Not to be assigned
 32768-49161  Standards Action         This range is for optional TLVs
                                       that can be silently dropped if
                                       not recognized.
 49162-64511  RFC Required             This range is for optional TLVs
                                       that can be silently dropped if
                                       not recognized.
 64512-65535  Private Use              Not to be assigned
 The initial allocations for this registry are:
 Sub-Type     Sub-TLV Name             Reference Comment
 --------     ------------             --------- -------
 0            Reserved                 RFC 8611
 1            Incoming Label Stack     RFC 8611
 2            Incoming Interface Index RFC 8611
 3-31743      Unassigned
 31744-32767                           RFC 8611  Reserved for
                                                 Private Use
 32768-64511  Unassigned
 64512-65535                           RFC 8611  Reserved for
                                                 Private Use
 Note: IETF does not prescribe how the Private Use sub-TLVs are
 handled; however, if a packet containing a sub-TLV from a Private Use
 ranges is received by an LSR that does not recognize the sub-TLV, an
 error message MAY be returned if the sub-TLV is from the range
 31744-32767, and the packet SHOULD be silently dropped if it is from
 the range 64511-65535.

Akiya, et al. Standards Track [Page 24] RFC 8611 LSP Ping for LAG June 2019

13.4.2. Interface and Label Stack Address Types

 The Detailed Interface and Label Stack TLV shares the Interface and
 Label Stack Address Types with the Interface and Label Stack TLV.  To
 reflect this, IANA has updated the name of the registry from
 "Interface and Label Stack Address Types" to "Interface and Label
 Stack and Detailed Interface and Label Stack Address Types".

13.5. DS Flags

 IANA has assigned a new bit number from the "DS Flags" subregistry of
 the "Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs)
 Ping Parameters" registry [IANA-MPLS-LSP-PING].
 Note: the "DS Flags" subregistry was created by [RFC8029].
  Bit number Name                                        Reference
  ---------- ----------------------------------------    ---------
       3     G: LAG Description Indicator                RFC 8611

14. References

14.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <https://www.rfc-editor.org/info/rfc2119>.
 [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
            Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
            Switched (MPLS) Data-Plane Failures", RFC 8029,
            DOI 10.17487/RFC8029, March 2017,
            <https://www.rfc-editor.org/info/rfc8029>.
 [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
            Writing an IANA Considerations Section in RFCs", BCP 26,
            RFC 8126, DOI 10.17487/RFC8126, June 2017,
            <https://www.rfc-editor.org/info/rfc8126>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <https://www.rfc-editor.org/info/rfc8174>.

Akiya, et al. Standards Track [Page 25] RFC 8611 LSP Ping for LAG June 2019

14.2. Informative References

 [IANA-MPLS-LSP-PING]
            IANA, "Multiprotocol Label Switching (MPLS) Label Switched
            Paths (LSPs) Ping Parameters",
            <https://www.iana.org/assignments/
            mpls-lsp-ping-parameters/>.
 [IEEE802.1AX]
            IEEE, "IEEE Standard for Local and metropolitan area
            networks - Link Aggregation", IEEE Std. 802.1AX.
 [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
            Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
            <https://www.rfc-editor.org/info/rfc5920>.
 [RFC6425]  Saxena, S., Ed., Swallow, G., Ali, Z., Farrel, A.,
            Yasukawa, S., and T. Nadeau, "Detecting Data-Plane
            Failures in Point-to-Multipoint MPLS - Extensions to LSP
            Ping", RFC 6425, DOI 10.17487/RFC6425, November 2011,
            <https://www.rfc-editor.org/info/rfc6425>.
 [RFC7439]  George, W., Ed. and C. Pignataro, Ed., "Gap Analysis for
            Operating IPv6-Only MPLS Networks", RFC 7439,
            DOI 10.17487/RFC7439, January 2015,
            <https://www.rfc-editor.org/info/rfc7439>.

Akiya, et al. Standards Track [Page 26] RFC 8611 LSP Ping for LAG June 2019

Appendix A. LAG with Intermediate L2 Switch Issues

 Several flavors of provisioning models that use a "LAG with L2
 switch" and the corresponding MPLS data-plane ECMP traversal
 validation issues are described in this appendix.

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 Router 1 (R1) to intermediate L2 switch (S1) can
 get load-balanced by S1 towards Router 2 (R2).  Therefore, MPLS echo
 request messages traversing a specific LAG member from R1 to S1 can
 actually reach R2 via any of the LAG members, and the sender of the
 MPLS echo request messages has no knowledge of this nor any way to
 control this traversal.  In the worst case, MPLS echo request
 messages with specific entropies will exercise every LAG member link
 from R1 to S1 and can all reach R2 via the same LAG member link.
 Thus, it is impossible for the MPLS echo request sender to verify
 that packets intended to traverse a specific LAG member link from R1
 to S1 did actually traverse that LAG member link and to
 deterministically exercise "receive" processing of every LAG member
 link on R2.  (Note: As far as we can tell, there's not a better
 option than "try a bunch of entropy labels and see what responses you
 can get back", and that's the same remedy in all the described
 topologies.)

A.2. Deviating Numbers of LAG Members

            ____
 R1 ==== S1 ==== R2
 There are deviating numbers of LAG members on the two sides of the L2
 switch.  The issue with this LAG provisioning model is the same as
 with the previous model: the sender of MPLS echo request messages has
 no knowledge of the L2 load-balancing 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 an MPLS echo request sender to deterministically exercise both
 LAG member links from S1 to R2.  And without such, "receive"
 processing of R2 on each LAG member cannot be verified.

Akiya, et al. Standards Track [Page 27] RFC 8611 LSP Ping for LAG June 2019

A.4. LAG Only on Left

 R1 ==== S1 ---- R2
 The 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
 the 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.

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 a
 number of comments.
 The authors also would like to extend sincere thanks to the MPLS RT
 review members who took the 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 mechanisms.  The
 suggestion by Yimin Shen to create two separate validation procedures
 had a big impact on the contents of this document.

Akiya, et al. Standards Track [Page 28] RFC 8611 LSP Ping for LAG June 2019

Authors' Addresses

 Nobo Akiya
 Big Switch Networks
 Email: nobo.akiya.dev@gmail.com
 George Swallow
 Southend Technical Center
 Email: swallow.ietf@gmail.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
 Mach(Guoyi) Chen
 Huawei
 Email: mach.chen@huawei.com

Akiya, et al. Standards Track [Page 29]

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