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rfc:rfc8012

Internet Engineering Task Force (IETF) N. Akiya Request for Comments: 8012 Big Switch Networks Updates: 6790 G. Swallow Category: Standards Track C. Pignataro ISSN: 2070-1721 Cisco

                                                              A. Malis
                                                   Huawei Technologies
                                                             S. Aldrin
                                                                Google
                                                         November 2016
      Label Switched Path (LSP) and Pseudowire (PW) Ping/Trace
           over MPLS Networks Using Entropy Labels (ELs)

Abstract

 Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) ping
 and traceroute are methods used to test Equal-Cost Multipath (ECMP)
 paths.  Ping is known as a connectivity-verification method and
 traceroute is known as a fault-isolation method, as described in RFC
 4379.  When an LSP is signaled using the Entropy Label (EL) described
 in RFC 6790, the ability for LSP ping and traceroute operations to
 discover and exercise ECMP paths is lost for scenarios where Label
 Switching Routers (LSRs) apply different load-balancing techniques.
 One such scenario is when some LSRs apply EL-based load balancing
 while other LSRs apply load balancing that is not EL based (e.g.,
 IP).  Another scenario is when an EL-based LSP is stitched with
 another LSP that can be EL based or not EL based.
 This document extends the MPLS LSP ping and traceroute multipath
 mechanisms in RFC 6424 to allow the ability of exercising LSPs that
 make use of the EL.  This document updates RFC 6790.

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
 http://www.rfc-editor.org/info/rfc8012.

Akiya, et al. Standards Track [Page 1] RFC 8012 LSP Ping over Entropy November 2016

Copyright Notice

 Copyright (c) 2016 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 ................................................5
         1.1.1. Requirements Language ...............................6
    1.2. Background .................................................6
 2. Multipath Type {9} ..............................................7
 3. Pseudowire Tracing ..............................................7
 4. Entropy Label FEC ...............................................8
 5. DS Flags: L and E ...............................................9
 6. New Multipath Information Type {10} ............................10
 7. Initiating LSR Procedures ......................................12
 8. Responder LSR Procedures .......................................14
    8.1. IP-Based Load Balancer That Does Not Push ELI/EL ..........15
    8.2. IP-Based Load Balancer That Pushes ELI/EL .................15
    8.3. Label-Based Load Balancer That Does Not Push ELI/EL .......16
    8.4. Label-Based Load Balancer That Pushes ELI/EL ..............17
    8.5. Flow-Aware MS-PW Stitching LSR ............................18
 9. Supported and Unsupported Cases ................................18
 10. Security Considerations .......................................20
 11. IANA Considerations ...........................................21
    11.1. Entropy Label FEC ........................................21
    11.2. DS Flags .................................................21
    11.3. Multipath Type ...........................................21
 12. References ....................................................22
    12.1. Normative References .....................................22
    12.2. Informative References ...................................22
 Acknowledgements ..................................................23
 Contributors ......................................................23
 Authors' Addresses ................................................23

Akiya, et al. Standards Track [Page 2] RFC 8012 LSP Ping over Entropy November 2016

1. Introduction

 [RFC4379] describes LSP traceroute as an operation where the
 initiating LSR sends a series of MPLS echo requests towards the same
 destination.  The first packet in the series has the TTL set to 1.
 When the echo reply is received from the LSR one hop away, the second
 echo request in the series is sent with the TTL set to 2.  For each
 additional echo request, the TTL is incremented by one until a
 response is received from the intended destination.  The initiating
 LSR discovers and exercises ECMP by obtaining Multipath Information
 from each transit LSR and using a specific destination IP address or
 specific entropy label.
 From here on, the notation {x, y, z} refers to Multipath Information
 Types x, y, or z.  Multipath Information Types are defined in
 Section 3.3 of [RFC4379] .
 The LSR initiating LSP ping sends an MPLS echo request with the
 Multipath Information.  This Multipath Information is described in
 the echo request's DDMAP TLV and may contain a set of IP addresses or
 a set of labels.  Multipath Information Types {2, 4, 8} carry a set
 of IP addresses, and the Multipath Information Type {9} carries a set
 of labels.  The responder LSR (the receiver of the MPLS echo request)
 will determine the subset of initiator-specified Multipath
 Information, which load balances to each downstream (outgoing)
 interface.  The responder LSR sends an MPLS echo reply with the
 resulting Multipath Information per downstream (outgoing interface)
 back to the initiating LSR.  The initiating LSR is then able to use a
 specific IP destination address or a specific label to exercise a
 specific ECMP path on the responder LSR.
 The current behavior is problematic in the following scenarios:
 o  The initiating LSR sends the IP Multipath Information, but the
    responder LSR load balances on labels.
 o  The initiating LSR sends the Label Multipath Information, but the
    responder LSR load balances on IP addresses.
 o  The initiating LSR sends the existing Multipath Information to an
    LSR that pushes ELI/EL in the label stack, but the initiating LSR
    can only continue to discover and exercise specific paths of the
    ECMP if the LSR that pushes ELI/EL responds with both IP addresses
    and the associated EL corresponding to each IP address.  This is
    because:
  • An ELI/EL-pushing LSR that is a stitching point will load

balance based on the IP address.

Akiya, et al. Standards Track [Page 3] RFC 8012 LSP Ping over Entropy November 2016

  • Downstream LSR(s) of an ELI/EL-pushing LSR may load balance

based on ELs.

 o  The initiating LSR sends existing Multipath Information to an ELI/
    EL-pushing LSR, but the initiating LSR can only continue to
    discover and exercise specific paths of ECMP if the ELI/EL-pushing
    LSR responds with both labels and the associated EL corresponding
    to the label.  This is because:
  • An ELI/EL-pushing LSR that is a stitching point will load

balance based on the EL from the previous LSP and push a new

       EL.
  • Downstream LSR(s) of ELI/EL-pushing LSR may load balance based

on new ELs.

 The above scenarios demonstrate that the existing Multipath
 Information is insufficient when LSP traceroute is used on an LSP
 with entropy labels [RFC6790].  This document defines a new Multipath
 Information Type to be used in the DDMAP of MPLS echo request/reply
 packets for [RFC6790] LSPs.
 The responder LSR can reply with empty Multipath Information if no IP
 address set or if no label set is received with the Multipath
 Information.  An empty return is also possible if an initiating LSR
 sends Multipath Information of one type, IP Address or Label, but the
 responder LSR load balances on the other type.  To disambiguate
 between the two results, this document introduces new flags in the
 DDMAP TLV to allow the responder LSR to describe the load-balancing
 technique being used.
 To use this enhanced method end-to-end, all LSRs along the LSP need
 to be able to understand the new flags and the new Multipath
 Information Type.  Mechanisms to verify this condition are outside of
 the scope of this document.  The rest of the requirements are
 detailed in the initiating LSR and responder LSR procedures.  Two
 additional DS Flags are defined for the DDMAP TLV in Section 6.
 These two flags are used by the responder LSR to describe its load-
 balancing behavior on a received MPLS echo request.
 Note that the terms "IP-Based Load Balancer" and "Label-Based Load
 Balancer" are in context of how a received MPLS echo request is
 handled by the responder LSR.

Akiya, et al. Standards Track [Page 4] RFC 8012 LSP Ping over Entropy November 2016

1.1. Terminology

 The following abbreviations and terms are used in this document:
 o  MPLS: Multiprotocol Label Switching.
 o  LSP: Label Switched Path.
 o  Stitched LSP: Stitched Label Switched Paths combine several LSPs
    such that a single end-to-end LSP is realized.  [RFC6424]
    describes LSP ping for Stitched LSPs.
 o  LSR: Label Switching Router.
 o  FEC: Forwarding Equivalence Class.
 o  ECMP: Equal-Cost Multipath.
 o  EL: Entropy Label.
 o  ELI: Entropy Label Indicator.
 o  GAL: Generic Associated Channel Label.
 o  MS-PW: Multi-Segment Pseudowire.
 o  Initiating LSR: An LSR that sends an MPLS echo request.
 o  Responder LSR: An LSR that receives an MPLS echo request and sends
    an MPLS echo reply.
 o  IP-Based Load Balancer: An LSR that load balances on fields from
    an IP header (and possibly fields from upper layers) and does not
    consider an entropy label from an MPLS label stack (i.e., flow
    label [RFC6391] or entropy label [RFC6790]) for load-balancing
    purposes.
 o  Label-Based Load Balancer: An LSR that load balances on an entropy
    label from an MPLS label stack (i.e., flow label or entropy label)
    and does not consider fields from an IP header (and possibly
    fields from upper layers) for load-balancing purposes.
 o  Label and IP-Based Load Balancer: An LSR that load balances on
    both entropy labels from an MPLS label stack and fields from an IP
    header (and possibly fields from upper layers).

Akiya, et al. Standards Track [Page 5] RFC 8012 LSP Ping over Entropy November 2016

1.1.1. 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].

1.2. Background

 MPLS implementations employ a wide variety of load-balancing
 techniques in terms of fields used for hash "keys".  The mechanisms
 in [RFC4379] and updated by [RFC6424] are designed to provide
 multipath support for a subset of techniques.  The intent of this
 document is to provide multipath support for the supported techniques
 that are compromised by the use of ELs [RFC6790].  Section 9
 describes supported and unsupported cases, and it may be useful for
 the reader to first review this section.
 The Downstream Detailed Mapping (DDMAP) TLV [RFC6424] provides
 Multipath Information, which can be used by an LSP ping initiator to
 trace and validate ECMP paths between an ingress and egress.  The
 Multipath Information encodings defined by [RFC6424] are sufficient
 when all the LSRs along the path(s), between ingress and egress,
 consider the same set of "keys" as input for load-balancing
 algorithms, e.g., either all IP based or all label based.
 With the introduction of [RFC6790], some LSRs may perform load
 balancing based on labels while others may be IP based.  This results
 in an LSP ping initiator that is unable to trace and validate all the
 ECMP paths in the following scenarios:
 o  One or more transit LSRs along an LSP with ELI/EL in the label
    stack do not perform ECMP load balancing based on EL (hashes based
    on "keys" including the IP destination address).  This scenario is
    not only possible but quite common due to transit LSRs not
    implementing [RFC6790] or transit LSRs implementing [RFC6790] but
    not implementing the suggested transit LSR behavior in Section 4.3
    of [RFC6790].
 o  Two or more LSPs stitched together with at least one of these LSPs
    pushing ELI/EL into the label stack.
 These scenarios can be quite common because deployments of [RFC6790]
 typically have a mixture of nodes that support ELI/EL and nodes that
 do not.  There will also typically be a mixture of areas that support
 ELI/EL and areas that do not.

Akiya, et al. Standards Track [Page 6] RFC 8012 LSP Ping over Entropy November 2016

 As pointed out in [RFC6790], the procedures of [RFC4379] (and
 consequently of [RFC6424]) with respect to Multipath Information Type
 {9} are incomplete.  However, [RFC6790] does not actually update
 [RFC4379].  Further, the specific EL location is not clearly defined,
 particularly in the case of Flow-Aware Pseudowires [RFC6391].  This
 document defines a new FEC Stack sub-TLV for the entropy label.
 Section 2 of this document updates the procedures for the Multipath
 Information Type {9} that are described in [RFC4379] and that are
 applicable to [RFC6424].  The rest of this document describes
 extensions required to restore ECMP discovery and tracing
 capabilities for the scenarios described.
 [RFC4379], [RFC6424], and this document will support IP-based load
 balancers and label-based load balancers that limit their hash to the
 first (top-most) or only entropy label in the label stack.  Other use
 cases (refer to Section 9) are out of scope.

2. Multipath Type {9}

 [RFC4379] defined Multipath Type {9} for the tracing of LSPs where
 label-based load balancing is used.  However, as pointed out in
 [RFC6790], the procedures for using this type are incomplete as the
 specific location of the label was not defined.  It was assumed that
 the presence of Multipath Type {9} implied that the value of the
 bottom-of-stack label should be varied by the values indicated by the
 multipath to determine the respective outgoing interfaces.
 Section 4 defines a new FEC-Stack sub-TLV to indicate an entropy
 label.  These labels MAY appear anywhere in a label stack.
 Multipath Type {9} applies to the first label in the label stack that
 corresponds to an EL-FEC.  If no such label is found, it applies to
 the label at the bottom of the label stack.

3. Pseudowire Tracing

 This section defines procedures for tracing Pseudowires.  These
 procedures pertain to the use of Multipath Information Type {9} as
 well as Type {10}.  In all cases below, when a control word is in
 use, the N flag in the DDMAP MUST be set.  Note that when a control
 word is not in use, the returned DDMAPs may not be accurate.
 In order to trace a Pseudowire that is not flow aware, the initiator
 includes an EL-FEC instead of the appropriate PW FEC at the bottom of
 the FEC Stack.  Tracing in this way will cause compliant routers to
 return the proper outgoing interface.  Note that this procedure only
 traces to the end of the MPLS LSP that is under test and will not
 verify the PW FEC.  To actually verify the PW FEC or in the case of a

Akiya, et al. Standards Track [Page 7] RFC 8012 LSP Ping over Entropy November 2016

 MS-PW, to determine the next Pseudowire label value, the initiator
 MUST repeat that step of the trace (i.e., repeating the TTL value
 used) but with the FEC Stack modified to contain the appropriate PW
 FEC.  Note that these procedures are applicable to scenarios where an
 initiator is able to vary the bottom label (i.e., Pseudowire label).
 Possible scenarios are tracing multiple Pseudowires that are not flow
 aware on the same endpoints or tracing a Pseudowire that is not flow-
 aware provisioned with multiple Pseudowire labels.
 In order to trace a flow-aware Pseudowire [RFC6391], the initiator
 includes an EL FEC at the bottom of the FEC Stack and pushes the
 appropriate PW FEC onto the FEC Stack.
 In order to trace through routers that are not compliant, the
 initiator forms an MPLS echo request message and includes a DDMAP
 with the Multipath Type {9}.  For a Pseudowire that is not flow
 aware, it includes the appropriate PW FEC in the FEC Stack.  For a
 flow- aware Pseudowire, the initiator includes a Nil FEC at the
 bottom of the FEC Stack and pushes the appropriate PW FEC onto the
 FEC Stack.

4. Entropy Label FEC

 The ELI is a reserved label that has no associated explicit FEC, and
 has the label value 7 assigned from the reserved range.  Use the Nil
 FEC as the Target FEC Stack sub-TLV to account for ELI in a Target
 FEC Stack TLV.
 The EL is a special-purpose label with the label value being
 discretionary (i.e., the label value is not from the reserved range).
 For LSP verification mechanics to perform its purpose, it is
 necessary for a Target FEC Stack sub-TLV to clearly describe the EL,
 particularly in the scenario where the label stack does not carry ELI
 (e.g., flow-aware Pseudowire [RFC6391]).  Therefore, this document
 defines an EL FEC sub-TLV (33, see Section 11.1) that allows a Target
 FEC Stack sub-TLV to be added to the Target FEC Stack to account for
 EL.

Akiya, et al. Standards Track [Page 8] RFC 8012 LSP Ping over Entropy November 2016

 The Length is 4.  Labels are 20-bit values treated as numbers.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 Label                 |          MBZ          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      Figure 1: Entropy Label FEC
 "Label" is the actual label value inserted in the label stack; the
 "MBZ" field MUST be zero when sent and ignored on receipt.

5. DS Flags: L and E

 Two flags, L and E, are added to the DS Flags field of the DDMAP TLV.
 Both flags MUST NOT be set in the echo request packets when sending
 and SHOULD be ignored when received.  Zero, one, or both new flags
 MUST be set in the echo reply packets.
  DS Flags
  --------
      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |  MBZ  |L|E|I|N|
     +-+-+-+-+-+-+-+-+
  Flag  Name and Meaning
  ----  ----------------
     L  Label-based load balance indicator
        This flag MUST be cleared in the echo request.  An LSR
        that performs load balancing on a label MUST set this
        flag in the echo reply.  An LSR that performs load
        balancing on IP MUST NOT set this flag in the echo
        reply.
     E  ELI/EL push indicator
        This flag MUST be cleared in the echo request.  An LSR
        that pushes ELI/EL MUST set this flag in the echo
        reply.  An LSR that does not push ELI/EL MUST NOT set
        this flag in the echo reply.

Akiya, et al. Standards Track [Page 9] RFC 8012 LSP Ping over Entropy November 2016

 The two flags result in four load-balancing techniques, which the
 echo reply generating LSR can indicate:
 o  {L=0, E=0} LSR load balances based on IP and does not push ELI/EL.
 o  {L=0, E=1} LSR load balances based on IP and pushes ELI/EL.
 o  {L=1, E=0} LSR load balances based on labels and does not push
    ELI/EL.
 o  {L=1, E=1} LSR load balances based on labels and pushes ELI/EL.

6. New Multipath Information Type {10}

 One new Multipath Information Type is added to be used in DDMAP TLV.
 This new Multipath Type has the value of 10.
   Key   Type                  Multipath Information
   ---   ----------------      ---------------------
   10    IP and Label set      IP addresses and label prefixes
 Multipath Information Type {10} is comprised of three sections.  The
 first section describes the IP address set.  The second section
 describes the label set.  The third section describes another label
 set, which associates to either the IP address set or the label set
 specified in the other sections.

Akiya, et al. Standards Track [Page 10] RFC 8012 LSP Ping over Entropy November 2016

 Multipath Information Type {10} 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |IPMultipathType|     IP Multipath Length       | Reserved(MBZ) |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                                                               ~
 |                  (IP Multipath Information)                   |
 ~                                                               ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |LbMultipathType|    Label Multipath Length     | Reserved(MBZ) |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                                                               ~
 |                 (Label Multipath Information)                 |
 ~                                                               ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Assoc. Label Multipath Length |         Reserved(MBZ)         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                                                               ~
 |            (Associated Label Multipath Information)           |
 ~                                                               ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 2: Multipath Information Type {10}
 o  IPMultipathType
  • 0 when "IP Multipath Information" is omitted. Otherwise, one

of the IP Multipath Information values: {2, 4, 8}.

 o  IP Multipath Information
  • This section is omitted when "IPMultipathType" is 0.

Otherwise, this section reuses the IP Multipath Information

       from [RFC4379].  Specifically, Multipath Information for values
       {2, 4, 8} can be used.
 o  LbMultipathType
  • 0 when the "Label Multipath Information" is omitted.

Otherwise, the Label Multipath Information value {9}.

Akiya, et al. Standards Track [Page 11] RFC 8012 LSP Ping over Entropy November 2016

 o  Label Multipath Information
  • This section is omitted when the "LbMultipathType" is 0.

Otherwise, this section reuses the Label Multipath Information

       from [RFC4379].  Specifically, the Multipath Information for
       value {9} can be used.
 o  Associated Label Multipath Information
  • "Associated Label Multipath Length" is a 16-bit field of

Multipath Information that indicates the length in octets of

       the Associated Label Multipath Information.
  • "Associated Label Multipath Information" is a list of labels

with each label described in 24 bits. This section MUST be

       omitted in an MPLS echo request message.  A midpoint that
       pushes ELI/EL labels SHOULD include "Associated Label Multipath
       Information" in its MPLS echo reply message, along with either
       "IP Multipath Information" or "Label Multipath Information".
       Each specified associated label described in this section maps
       to a specific IP address OR label described in the "IP
       Multipath Information" section or the "Label Multipath
       Information" section.  For example, if three IP addresses are
       specified in the "IP Multipath Information" section, then there
       MUST be three labels described in this section.  The first
       label maps to the first IP address specified, the second label
       maps to the second IP address specified, and the third label
       maps to the third IP address specified.
 When a section is omitted, the length for that section MUST be set to
 zero.

7. Initiating LSR Procedures

 The following procedure is described in terms of an EL_LSP boolean
 maintained by the initiating LSR.  This value controls the Multipath
 Information Type to be used in the transmitted echo request packets.
 When the initiating LSR is transmitting an echo request packet with
 DDMAP with a non-zero Multipath Information Type, then the EL_LSP
 boolean MUST be consulted to determine the Multipath Information Type
 to use.

Akiya, et al. Standards Track [Page 12] RFC 8012 LSP Ping over Entropy November 2016

 In addition to the procedures described in [RFC4379], as updated by
 Section 2 and [RFC6424], the initiating LSR MUST operate with the
 following procedures:
 o  When the initiating LSR pushes ELI/EL, initialize EL_LSP=True.
    Else, set EL_LSP=False.
 o  When the initiating LSR is transmitting a non-zero Multipath
    Information Type:
  • If (EL_LSP), the initiating LSR MUST use the Multipath

Information Type {10} unless the responder LSR cannot handle

       Type {10}.  When the initiating LSR is transmitting the
       Multipath Information Type {10}, both "IP Multipath
       Information" and "Label Multipath Information" MUST be
       included, and "Associated Label Multipath Information" MUST be
       omitted (NULL).
  • Else, the initiating LSR MAY use the Multipath Information Type

{2, 4, 8, 9, 10}. When the initiating LSR is transmitting the

       Multipath Information Type {10} in this case, "IP Multipath
       Information" MUST be included, and "Label Multipath
       Information" and "Associated Label Multipath Information" MUST
       be omitted (NULL).
 o  When the initiating LSR receives an echo reply with {L=0, E=1} in
    the DS Flags with valid contents, set EL_LSP=True.
 In the following conditions, the initiating LSR may have lost the
 ability to exercise specific ECMP paths.  The initiating LSR MAY
 continue with "best effort" in the following cases:
 o  Received echo reply contains empty Multipath Information.
 o  Received echo reply contains {L=0, E=<any>} DS Flags, but does not
    contain IP Multipath Information.
 o  Received echo reply contains {L=1, E=<any>} DS Flags, but does not
    contain Label Multipath Information.
 o  Received echo reply contains {L=<any>, E=1} DS Flags, but does not
    contain Associated Label Multipath Information.
 o  IP Multipath Information Types {2, 4, 8} sent, and received echo
    reply with {L=1, E=0} in DS Flags.
 o  Multipath Information Type {10} sent, and received echo reply with
    Multipath Information Type other than {10}.

Akiya, et al. Standards Track [Page 13] RFC 8012 LSP Ping over Entropy November 2016

8. Responder LSR Procedures

 Common Procedures:
 o  The responder LSR receiving an MPLS echo request packet MUST first
    determine whether or not the initiating LSR supports this LSP ping
    and traceroute extension for entropy labels.  If either of the
    following conditions are met, the responder LSR SHOULD determine
    that the initiating LSR supports this LSP ping and traceroute
    extension for entropy labels.
    1.  Received MPLS echo request contains the Multipath Information
        Type {10}.
    2.  Received MPLS echo request contains a Target FEC Stack TLV
        that includes the entropy label FEC.
    If the initiating LSR is determined not to support this LSP ping
    and traceroute extension for entropy labels, then the responder
    LSR MUST NOT follow further procedures described in this section.
    Specifically, MPLS echo reply packets:
  • MUST have the following DS Flags cleared (i.e., not set): "ELI/

EL push indicator" and "Label-based load balance indicator".

  • MUST NOT use the Multipath Information Type {10}.
 o  The responder LSR receiving an MPLS echo request packet with the
    Multipath Information Type {10} MUST validate the following
    contents.  Any deviation MUST result in the responder LSR
    considering the packet to be malformed and returning code 1
    ("Malformed echo request received") in the MPLS echo reply packet.
  • IP Multipath Information MUST be included.
  • Label Multipath Information MAY be included.
  • Associated Label Multipath Information MUST be omitted (NULL).
 The following subsections describe expected responder LSR procedures
 when the echo reply is to include DDMAP TLVs, based on the local load
 balance technique being employed.  In case the responder LSR performs
 deviating load balance techniques on a per-downstream basis,
 appropriate procedures matched to each downstream load balance
 technique MUST be followed.

Akiya, et al. Standards Track [Page 14] RFC 8012 LSP Ping over Entropy November 2016

8.1. IP-Based Load Balancer That Does Not Push ELI/EL

 o  The responder MUST set {L=0, E=0} in DS Flags.
 o  If the Multipath Information Type {2, 4, 8} is received, the
    responder MUST comply with [RFC4379] and [RFC6424].
 o  If the Multipath Information Type {9} is received, the responder
    MUST reply with Multipath Type {0}.
 o  If the Multipath Information Type {10} is received, the following
    procedures are to be used:
  • The responder MUST reply with the Multipath Information Type

{10}.

  • The "Label Multipath Information" and "Associated Label

Multipath Information" sections MUST be omitted (NULL).

  • If no matching IP address is found, then the "IPMultipathType"

field MUST be set to the Multipath Information Type {0} and the

       "IP Multipath Information" section MUST also be omitted (NULL).
  • If at least one matching IP address is found, then the

"IPMultipathType" field MUST be set to the appropriate

       Multipath Information Type {2, 4, 8} and the "IP Multipath
       Information" section MUST be included.

8.2. IP-Based Load Balancer That Pushes ELI/EL

 o  The responder MUST set {L=0, E=1} in DS Flags.
 o  If the Multipath Information Type {9} is received, the responder
    MUST reply with Multipath Type {0}.
 o  If the Multipath Type {2, 4, 8, 10} is received, the following
    procedures are to be used:
  • The responder MUST respond with Multipath Type {10}. See

Section 6 for details of Multipath Type {10}.

  • The "Label Multipath Information" section MUST be omitted

(i.e., it is not there).

  • The IP address set specified in the received IP Multipath

Information MUST be used to determine the returned IP/Label

       pairs.

Akiya, et al. Standards Track [Page 15] RFC 8012 LSP Ping over Entropy November 2016

  • If the received Multipath Information Type was {10}, the

received "Label Multipath Information" sections MUST NOT be

       used to determine the associated label portion of the returned
       IP/Label pairs.
  • If no matching IP address is found, then the "IPMultipathType"

field MUST be set to the Multipath Information Type {0} and the

       "IP Multipath Information" section MUST be omitted.  In
       addition, the "Associated Label Multipath Length" MUST be set
       to 0, and the "Associated Label Multipath Information" section
       MUST also be omitted.
  • If at least one matching IP address is found, then the

"IPMultipathType" field MUST be set to the appropriate

       Multipath Information Type {2, 4, 8} and the "IP Multipath
       Information" section MUST be included.  In addition, the
       "Associated Label Multipath Information" section MUST be
       populated with a list of labels corresponding to each IP
       address specified in the "IP Multipath Information" section.
       "Associated Label Multipath Length" MUST be set to a value
       representing the length in octets of the "Associated Label
       Multipath Information" field.

8.3. Label-Based Load Balancer That Does Not Push ELI/EL

 o  The responder MUST set {L=1, E=0} in DS Flags.
 o  If the Multipath Information Type {2, 4, 8} is received, the
    responder MUST reply with Multipath Type {0}.
 o  If the Multipath Information Type {9} is received, the responder
    MUST comply with [RFC4379] and [RFC6424] as updated by Section 2.
 o  If the Multipath Information Type {10} is received, the following
    procedures are to be used:
  • The responder MUST reply with the Multipath Information Type

{10}.

  • The "IP Multipath Information" and "Associated Label Multipath

Information" sections MUST be omitted (NULL).

  • If no matching label is found, then the "LbMultipathType" field

MUST be set to the Multipath Information Type {0} and the

       "Label Multipath Information" section MUST also be omitted
       (NULL).

Akiya, et al. Standards Track [Page 16] RFC 8012 LSP Ping over Entropy November 2016

  • If at least one matching label is found, then the

"LbMultipathType" field MUST be set to the appropriate

       Multipath Information Type {9} and the "Label Multipath
       Information" section MUST be included.

8.4. Label-Based Load Balancer That Pushes ELI/EL

 o  The responder MUST set {L=1, E=1} in DS Flags.
 o  If the Multipath Information Type {2, 4, 8} is received, the
    responder MUST reply with Multipath Type {0}.
 o  If the Multipath Type {9, 10} is received, the following
    procedures are to be used:
  • The responder MUST respond with the Multipath Type {10}.
  • The "IP Multipath Information" section MUST be omitted.
  • The label set specified in the received Label Multipath

Information MUST be used to determine the returned Label/Label

       pairs.
  • If the received Multipath Information Type was {10} received,

the "Label Multipath Information" sections MUST NOT be used to

       determine the associated label portion of the returned Label/
       Label pairs.
  • If no matching label is found, then the "LbMultipathType" field

MUST be set to the Multipath Information Type {0} and the

       "Label Multipath Information" section MUST be omitted.  In
       addition, the "Associated Label Multipath Length" MUST be set
       to 0, and the "Associated Label Multipath Information" section
       MUST also be omitted.
  • If at least one matching label is found, then the

"LbMultipathType" field MUST be set to the appropriate

       Multipath Information Type {9} and the "Label Multipath
       Information" section MUST be included.  In addition, the
       "Associated Label Multipath Information" section MUST be
       populated with a list of labels corresponding to each label
       specified in the "Label Multipath Information" section.  The
       "Associated Label Multipath Length" MUST be set to a value
       representing the length in octets of the "Associated Label
       Multipath Information" field.

Akiya, et al. Standards Track [Page 17] RFC 8012 LSP Ping over Entropy November 2016

8.5. Flow-Aware MS-PW Stitching LSR

 A stitching LSR that cross-connects flow-aware Pseudowires behaves in
 one of two ways:
 o  Load balances on the previous flow label and carries over the same
    flow label.  For this case, the stitching LSR is to behave as
    described in Section 8.3.
 o  Load balances on the previous flow label and replaces the flow
    label with a newly computed label.  For this case, the stitching
    LSR is to behave as described in Section 8.4.

9. Supported and Unsupported Cases

 The MPLS architecture does not define strict rules on how
 implementations are to identify hash "keys" for load-balancing
 purposes.  As a result, implementations may be of the following load
 balancer types:
 1.  IP-based load balancer.
 2.  Label-based load balancer.
 3.  Label- and IP-based load balancer.
 For cases (2) and (3), an implementation can include different sets
 of labels from the label stack for load-balancing purpose.  Thus, the
 following sub-cases are possible:
 a.  Entire label stack.
 b.  Top N labels from label stack where the number of labels in label
     stack is > N.
 c.  Bottom N labels from label stack where the number of labels in
     label stack is > N.
 In a scenario where there is one flow label or entropy label present
 in the label stack, the following further cases are possible for
 (2b), (2c), (3b), and (3c):
 1.  N labels from label stack include flow label or entropy label.
 2.  N labels from label stack do not include flow label or entropy
     label.

Akiya, et al. Standards Track [Page 18] RFC 8012 LSP Ping over Entropy November 2016

 Also, in a scenario where there are multiple entropy labels present
 in the label stack, it is possible for implementations to employ
 deviating techniques:
 o  Search for entropy stops at the first entropy label.
 o  Search for entropy includes any entropy label found plus continues
    to search for entropy in the label stack.
 Furthermore, handling of reserved (i.e., special) labels varies among
 implementations:
 o  Reserved labels are used in the hash as any other label would be
    (not a recommended practice).
 o  Reserved labels are skipped over and, for implementations limited
    to N labels, the reserved labels do not count towards the limit of
    N.
 o  Reserved labels are skipped over and, for implementations limited
    to N labels, the reserved labels count towards the limit of N.
 It is important to point this out since the presence of GAL will
 affect those implementations that include reserved labels for load-
 balancing purposes.
 As can be seen from the above, there are many types of potential
 load-balancing implementations.  Attempting to get any Operations,
 Administration, and Maintenance (OAM) tools to support ECMP discovery
 and traversal over all types would require fairly complex procedures.
 Complexities in OAM tools have minimal benefit if the majority of
 implementations are expected to employ only a small subset of the
 cases described above.
 o  Section 4.3 of [RFC6790] states that in implementations, for load-
    balancing purposes, parsing beyond the label stack after finding
    an entropy label has "limited incremental value".  Therefore, it
    is expected that most implementations will be of types "IP-based
    load balancer" or "Label-based load balancer".
 o  Section 2.4.5.1 of [RFC7325] recommends that searching for entropy
    labels in the label stack should terminate upon finding the first
    entropy label.  Therefore, it is expected that implementations
    will only include the first (top-most) entropy label when there
    are multiple entropy labels in the label stack.

Akiya, et al. Standards Track [Page 19] RFC 8012 LSP Ping over Entropy November 2016

 o  It is expected that, in most cases, the number of labels in the
    label stack will not exceed the number of labels (N) that
    implementations can include for load-balancing purposes.
 o  It is expected that labels in the label stack, besides the flow
    label and entropy label, are constant for the lifetime of a single
    LSP multipath traceroute operation.  Therefore, deviating load-
    balancing implementations with respect to reserved labels should
    not affect this tool.
 Thus, [RFC4379], [RFC6424], and this document support cases (1) and
 (2a1), where only the first (top-most) entropy label is included when
 there are multiple entropy labels in the label stack.

10. Security Considerations

 While [RFC4379] and [RFC6424] already allow for the discovery and
 exercise of ECMP paths, this document extends the LSP ping and
 traceroute mechanisms to more precisely discover and exercise ECMP
 paths when an LSP uses ELI/EL in the label stack.  Sourcing or
 inspecting LSP ping packets can be used for network reconnaissance.
 The extended capability defined in this document requires minor
 additional processing for the responder and initiator nodes.  The
 responder node that pushes ELI/EL will need to compute and return
 multipath data including associated EL.  The initiator node will need
 to store and handle both IP Multipath and Label Multipath
 Information, and include destination IP addresses and/or ELs in MPLS
 echo request packets as well as in the Multipath Information sent to
 downstream nodes.  The security considerations of [RFC4379] already
 cover Denial-of-Service attacks by regulating LSP ping traffic going
 to the control plane.
 Finally, the security measures described in [RFC4379], [RFC6424], and
 [RFC6790] are applicable.  [RFC6424] provides guidelines if a network
 operator wants to prevent tracing or does not want to expose details
 of the tunnel and [RFC6790] provides guidance on the use of the EL.

Akiya, et al. Standards Track [Page 20] RFC 8012 LSP Ping over Entropy November 2016

11. IANA Considerations

11.1. Entropy Label FEC

 IANA has assigned a new sub-TLV from the "Sub-TLVs for TLV Types 1,
 16, and 21" section from the "Multi-Protocol Label Switching (MPLS)
 Label Switched Paths (LSPs) Ping Parameters" registry under "TLVs"
 ([IANA-MPLS-LSP-PING]).
  Sub-Type Sub-TLV Name          Reference
  -------- ------------          ---------
     33     Entropy label FEC     this document

11.2. DS Flags

 IANA has assigned new bit numbers from the "DS Flags" subregistry
 from the "TLVs" section of the "Multi-Protocol Label Switching (MPLS)
 Label Switched Paths (LSPs) Ping Parameters" registry
 ([IANA-MPLS-LSP-PING]).
 Note: The "DS Flags" subregistry was created by [RFC7537].
 Bit number Name                                        Reference
 ---------- ----------------------------------------    ---------
     5       E: ELI/EL push indicator                    this document
     4       L: Label-based load balance indicator       this document

11.3. Multipath Type

 IANA has assigned a new value from the "Multipath Type" subregistry
 from the "TLVs" section of the "Multi-Protocol Label Switching (MPLS)
 Label Switched Paths (LSPs) Ping Parameters" registry
 ([IANA-MPLS-LSP-PING]).
 Note: The "Multipath Type" subregistry was created by [RFC7537].
  Value      Meaning                                  Reference
  ---------- ---------------------------------------- ---------
    10       IP and label set                         this document

Akiya, et al. Standards Track [Page 21] RFC 8012 LSP Ping over Entropy November 2016

12. References

12.1. 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,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol
            Label Switched (MPLS) Data Plane Failures", RFC 4379,
            DOI 10.17487/RFC4379, February 2006,
            <http://www.rfc-editor.org/info/rfc4379>.
 [RFC6424]  Bahadur, N., Kompella, K., and G. Swallow, "Mechanism for
            Performing Label Switched Path Ping (LSP Ping) over MPLS
            Tunnels", RFC 6424, DOI 10.17487/RFC6424, November 2011,
            <http://www.rfc-editor.org/info/rfc6424>.
 [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
            L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
            RFC 6790, DOI 10.17487/RFC6790, November 2012,
            <http://www.rfc-editor.org/info/rfc6790>.
 [RFC7537]  Decraene, B., Akiya, N., Pignataro, C., Andersson, L., and
            S. Aldrin, "IANA Registries for LSP Ping Code Points",
            RFC 7537, DOI 10.17487/RFC7537, May 2015,
            <http://www.rfc-editor.org/info/rfc7537>.

12.2. Informative References

 [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>.
 [RFC6391]  Bryant, S., Ed., Filsfils, C., Drafz, U., Kompella, V.,
            Regan, J., and S. Amante, "Flow-Aware Transport of
            Pseudowires over an MPLS Packet Switched Network",
            RFC 6391, DOI 10.17487/RFC6391, November 2011,
            <http://www.rfc-editor.org/info/rfc6391>.
 [RFC7325]  Villamizar, C., Ed., Kompella, K., Amante, S., Malis, A.,
            and C. Pignataro, "MPLS Forwarding Compliance and
            Performance Requirements", RFC 7325, DOI 10.17487/RFC7325,
            August 2014, <http://www.rfc-editor.org/info/rfc7325>.

Akiya, et al. Standards Track [Page 22] RFC 8012 LSP Ping over Entropy November 2016

Acknowledgements

 The authors would like to thank Loa Andersson, Curtis Villamizar,
 Daniel King, Sriganesh Kini, Victor Ji, Acee Lindem, Deborah
 Brungard, Shawn M Emery, Scott O. Bradner, and Peter Yee for
 performing thorough reviews and providing very valuable comments.
 Carlos Pignataro would like to acknowledge his lifetime friend Martin
 Rigueiro, with deep gratitude and esteem, for sharing his contagious
 passion for engineering and sciences, and for selflessly teaching so
 many lessons.

Contributors

 Nagendra Kumar
 Cisco Systems, Inc.
 Email: naikumar@cisco.com

Authors' Addresses

 Nobo Akiya
 Big Switch Networks
 Email: nobo.akiya.dev@gmail.com
 George Swallow
 Cisco Systems, Inc.
 Email: swallow@cisco.com
 Carlos Pignataro
 Cisco Systems, Inc.
 Email: cpignata@cisco.com
 Andrew G. Malis
 Huawei Technologies
 Email: agmalis@gmail.com
 Sam Aldrin
 Google
 Email: aldrin.ietf@gmail.com

Akiya, et al. Standards Track [Page 23]

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