path: root/doc/rfc/rfc7555.txt

Internet Engineering Task Force (IETF)                        G. Swallow
Request for Comments: 7555                                        V. Lim
Category: Standards Track                                  Cisco Systems
ISSN: 2070-1721                                                S. Aldrin
                                                     Huawei Technologies
                                                               June 2015


                        Proxy MPLS Echo Request

Abstract

   This document defines a means of remotely initiating Multiprotocol
   Label Switched Protocol (MPLS) Pings on Label Switched Paths.  An
   MPLS Proxy Ping Request is sent to any Label Switching Router along a
   Label Switched Path.  The primary motivations for this facility are
   first to limit the number of messages and related processing when
   using LSP Ping in large Point-to-Multipoint LSPs, and second to
   enable tracing from leaf to leaf (or root).

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 5741.

   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/rfc7555.

Copyright Notice

   Copyright (c) 2015 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.



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Table of Contents

   1. Introduction ....................................................3
      1.1. Requirements Language ......................................4
      1.2. Terminology ................................................5
   2. Proxy Ping Overview .............................................5
      2.1. Initiating Proxy Ping ......................................6
      2.2. Handling at Proxy LSR ......................................6
           2.2.1. Backward Compatibility ..............................6
   3. Proxy MPLS Echo Request/Reply Procedures ........................7
      3.1. Procedures for the Initiator ...............................7
      3.2. Procedures for the Proxy LSR ...............................9
           3.2.1. Proxy LSR Handling When It Is Egress for FEC .......11
           3.2.2. Downstream Detailed Maps and Downstream
                  Maps in Proxy Reply ................................12
           3.2.3. Sending an MPLS Proxy Ping Reply ...................12
           3.2.4. Sending the MPLS Echo Requests .....................13
                  3.2.4.1. Forming the Base MPLS Echo Request ........13
                  3.2.4.2. Per-Interface Sending Procedures ..........14
   4. Proxy Ping Request/Reply Messages ..............................15
      4.1. Proxy Ping Request/Reply Message Formats ..................15
      4.2. Proxy Ping Request Message Contents .......................15
      4.3. Proxy Ping Reply Message Contents .........................16
   5. TLV Formats ....................................................16
      5.1. Proxy Echo Parameters TLV .................................16
           5.1.1. Next Hop Sub-TLV ...................................20
      5.2. Reply-to Address TLV ......................................21
      5.3. Upstream Neighbor Address TLV .............................21
      5.4. Downstream Neighbor Address TLV ...........................22
   6. Security Considerations ........................................23
   7. IANA Considerations ............................................24
      7.1. Proxy Echo Parameters Sub-TLVs ............................24
      7.2. Proxy Flags ...............................................25
      7.3. Downstream Address Mapping Registry .......................25
      7.4. Next Hop Sub-TLV Address Type Registry ....................25
   8. References .....................................................26
      8.1. Normative References ......................................26
      8.2. Informative References ....................................27
   Acknowledgements ..................................................27
   Authors' Addresses ................................................28











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1.  Introduction

   This document is motivated by two broad issues in connection with
   diagnosing Point-to-Multipoint (P2MP) Label Switched Paths (LSPs).
   The first is scalability due to the automatic replication of
   Multiprotocol Label Switching (MPLS) Echo Request messages as they
   proceed down the tree.  The second, which is primarily motivated by
   LDP-based P2MP and Multipoint-to-Multipoint (MP2MP) LSPs [RFC6388],
   is the ability to trace a sub-LSP from leaf node to root node.

   When tracing from a source to a particular leaf in a P2MP or MP2MP
   tree, nodes not along that path will need to process MPLS Echo
   Request messages that are received.  The number of MPLS Echo Replies
   sent in response to an MPLS Echo Request quickly multiplies, as the
   Label Switching Routers (LSRs), which are part of the tree but not
   along the path of the trace, could be responding to the received MPLS
   Echo Request as well.  This could also overwhelm the source to
   process all the MPLS Echo Reply messages it receives.  It is
   anticipated that many of the applications for P2MP/MP2MP tunnels will
   require OAM that is both rigorous and scalable.

   Suppose one wishes to trace a P2MP LSP to localize a fault that is
   affecting one egress or a set of egresses.  Suppose one follows the
   normal procedure for tracing -- namely, repeatedly pinging from the
   root, incrementing the Time to Live (TTL) by one after each three or
   so pings.  Such a procedure has the potential for producing a large
   amount of processing at the P2MP-LSP midpoints and egresses.  It also
   could produce an unwieldy number of replies back to the root.

   One alternative would be to begin sending pings from points at or
   near the affected egress(es) and then work backwards toward the root.
   The TTL could be held constant (say, two), limiting the number of
   responses to the number of next-next-hops of the point where a ping
   is initiated.

   In the case of Resource Reservation Protocol Traffic Engineering
   (RSVP-TE), all setup is initiated from the root of the tree.  Thus,
   the root of the tree has knowledge of all the leaf nodes and usually
   the topology of the entire tree.  Thus, the above alternative can
   easily be initiated by the root node.

   In [RFC6388], the situation is quite different.  Leaf nodes initiate
   connectivity to the tree, which is granted by the first node toward
   the root that is part of the tree.  The root node may only be aware
   of the immediately adjacent (downstream) nodes of the tree.
   Initially, the leaf node only has knowledge of the (upstream) node to
   which it is immediately adjacent.  However, this is sufficient
   information to initiate a trace.  First, the above procedure is



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   applied by asking that node to ping across the final link.  That is,
   a message is sent from the leaf to the upstream node requesting it to
   send an MPLS Echo Request for the Forward Equivalence Class (FEC) of
   the tree in question on said link.  The leaf node also requests the
   identity of the upstream neighbor's upstream neighbor for that FEC.
   With this information, the procedure can iteratively be applied until
   the fault is localized or the root node is reached.  In all cases,
   the TTL for the request need only be at most 2.  Thus, the processing
   load of each request is small, since only a limited number of nodes
   will receive the request.

   This document defines protocol extensions to MPLS ping [RFC4379] to
   allow a third party to remotely cause an MPLS Echo Request message to
   be sent down an LSP or part of an LSP.  The procedure described in
   the paragraphs above does require that the initiator know the
   previous-hop node to the one which was pinged on the prior iteration.
   This information is readily available in [RFC4875].  This document
   also provides a means for obtaining this information for P2MP and
   MP2MP LSPs that are set up with LDP as described in [RFC6388].

   While the motivation for this document came from multicast scaling
   concerns, its applicability may be wider.  The procedures presented
   in this document are applicable to all LSP Ping FEC types where the
   MPLS Echo Request/Reply are IP encapsulated and the MPLS Echo Reply
   can be sent out of band of the LSP over IP.  Remote pinging of LSPs
   that involves the use of in-band control channels is beyond the scope
   of this document.

   Other uses of this facility are beyond the scope of this document.
   In particular, the procedures defined in this document only allow
   testing of a FEC stack consisting of a single FEC.  The procedures
   also do not allow the initiator to specify the label assigned to that
   FEC, nor do the procedures allow the initiator to cause any
   additional labels to be added to the label stack of the actual MPLS
   Echo Request message.

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 [RFC2119].

   The term "Must Be Zero" (MBZ) is used in TLV descriptions for
   reserved fields.  These fields MUST be set to zero when sent and
   ignored on receipt.






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   Based on context, the terms "leaf" and "egress" are used
   interchangeably.  "Egress" is used where consistency with [RFC4379]
   was deemed appropriate.  "Receiver" is used in the context of
   receiving protocol messages.

1.2.  Terminology

      Term  Definition
      ----- -------------------------------------------
      LSP   Label Switched Path
      LSR   Label Switching Router
      mLDP  Multipoint LDP
      MP2MP Multipoint to Multipoint
      MTU   Maximum Transmission Unit
      P2MP  Point to Multipoint
      TTL   Time to Live

2.  Proxy Ping Overview

   This document defines a protocol interaction between a first LSR and
   another LSR that is part of an LSP in order to allow the first LSR to
   request that the second LSR initiate an LSP Ping for the LSP on the
   first LSR's behalf.  Since the second LSR sends the LSP Ping on
   behalf of the first LSR, it does not maintain state to be able to
   handle the corresponding LSP Ping response.  Instead, the responder
   to the LSP Ping sends the LSP Ping response to either the first LSR
   or another LSR configured to handle it.  Two new LSP Ping messages
   are defined for remote pinging: the MPLS Proxy Ping Request and the
   MPLS Proxy Ping Reply.

   A remote ping operation on a P2MP LSP generally involves at least
   three LSRs; in some scenarios, none of these are the ingress (root)
   or an egress (leaf) of the LSP.

   We refer to these LSRs with the following terms:

      Initiator - the LSR that initiates the ping operation by sending
      an MPLS Proxy Ping Request message

      Proxy LSR - the LSR that is the destination of the MPLS Proxy Ping
      Request message and the potential initiator of the MPLS Echo
      Request

      Receiver(s) - the LSR(s) that receive the MPLS Echo Request
      message

      Responder - A receiver that responds to an MPLS Proxy Ping Request
      or an MPLS Echo Request



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   We note that in some scenarios, the initiator could also be the
   responder; in that case, the response would be internal to the LSR.

2.1.  Initiating Proxy Ping

   The initiator formats an MPLS Proxy Ping Request message and sends it
   to the Proxy LSR, an LSR it believes to be on the path of the LSP.
   This message instructs the Proxy LSR either to reply with Proxy
   information or to send an MPLS Echo Request in-band of the LSP.  The
   initiator requests Proxy information so that it can learn additional
   information it needs to use to form a subsequent MPLS Proxy Ping
   Request.  For example, during LSP traceroute, an initiator needs the
   downstream map information to form an MPLS Echo Request.  An
   initiator may also want to learn a Proxy LSR's FEC neighbor
   information so that it can form Proxy Ping Requests to various LSRs
   along the LSP.

2.2.  Handling at Proxy LSR

   The Proxy LSR either replies with the requested Proxy information or
   validates that it has a label mapping for the specified FEC and that
   it is authorized to send the specified MPLS Echo Request on behalf of
   the initiator.

   If the Proxy LSR has a label mapping for the FEC and all
   authorization checks have passed, the Proxy LSR formats an MPLS Echo
   Request.  If the source address of the MPLS Echo Request is not set
   to the Proxy Request source address, the initiator MUST include a
   Reply-to Address TLV containing the source address to use in the MPLS
   Echo Request.  It then sends the MPLS Echo Request in-band of the
   LSP.

   The receivers process the MPLS Echo Request as normal, sending their
   MPLS Echo Replies back to the initiator.

   If the Proxy LSR failed to send an MPLS Echo Request as normal
   because it encountered an issue while attempting to send, an MPLS
   Proxy Ping Reply message is sent back with a Return Code indicating
   that the MPLS Echo Request could not be sent.

2.2.1.  Backward Compatibility

   As described in Section 4.4 of [RFC4379], if the packet is not well-
   formed, LSR X SHOULD send an MPLS Echo Reply with the Return Code set
   to "Malformed echo request received" and the Return Subcode to zero.
   If there are any TLVs not marked as "Ignore" that the Proxy LSR does
   not understand, the Proxy LSR SHOULD send an MPLS "TLV not
   understood" (as appropriate), and the Return Subcode is set to zero.



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   In the case where the targeted Proxy LSR does not understand the LSP
   Ping Echo Request at all, like any other LSR that does not understand
   the messages, it MUST drop the message and MUST NOT send any message
   back to the initiator.

3.  Proxy MPLS Echo Request/Reply Procedures

3.1.  Procedures for the Initiator

   The initiator creates an MPLS Proxy Ping request message.

   The message MUST contain a Target FEC Stack that describes the FEC
   being tested.  The topmost FEC in the target FEC stack is used at the
   Proxy LSR to look up the MPLS label stack that will be used to
   encapsulate the MPLS Echo Request packet.

   The MPLS Proxy Ping Request message MUST contain a Proxy Echo
   Parameters TLV.  In that TLV, the address type is set to either IPv4
   or IPv6.  The Destination IP Address is set to the value to be used
   by the Proxy LSR to build the MPLS Echo Request packet.  The MPLS
   Echo Request IP header destination address is as specified in
   [RFC4379].  If the Address Type is IPv4, it MUST be an address is
   from the range 127/8; if the Address Type is IPv6, MUST be an address
   from the range ::ffff:7f00:0/104.

   The Reply Mode and Global Flags of the Proxy Echo Parameters TLV are
   set to the values to be used in the MPLS Echo Request message header.
   The Source UDP Port is set to the value to be used in the MPLS Echo
   Request (the source port is supplied by the Proxy Ping initiator
   because it or an LSR known to it handles the LSP Ping responses).
   The TTL is set to the value to be used in the outgoing MPLS label
   stack.  See Section 5.1 for further details.

   If the FEC's Upstream/Downstream Neighbor address information is
   required, the initiator sets the "Request for FEC neighbor
   information" Proxy Flags in the Proxy Echo Parameters TLV.

   If a Downstream Detailed Mapping TLV (or Downstream Mapping TLV,
   which is deprecated) is required in an MPLS Proxy Ping Reply, the
   initiator sets the "Request for Downstream Detailed Mapping" (or
   "Request for Downstream Mapping") Proxy Flag in the Proxy Echo
   Parameters TLV.  Only one of the two flags can be set.

   The Proxy Request Reply Mode is set with one of the Reply Modes
   defined in [RFC4379] as appropriate.






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   A list of next-hop IP addresses MAY be included to limit the next
   hops towards which the MPLS Echo Request message will be sent.  These
   are encoded as Next Hop sub-TLVs and included in the Proxy Echo
   Parameters TLV.

   Although not explicitly spelled out in [RFC4379], LSP Ping packets
   can be formed to a desired size using a Pad TLV and then used to test
   the Maximum Transmission Unit (MTU) of an LSP.  When testing an LSP's
   MTU, if the message is transported as an IP datagram, the IP header
   DF bit MUST be set to prevent IP fragmentation by the IP forwarding
   layer.  The Proxy Echo Parameter TLV MPLS Payload Size field is
   defined for this purpose and may be set to request that the MPLS Echo
   Request (including any IP and UDP header) be zero-padded to the
   specified size.  When a non-zero MPLS payload size is specified, the
   Proxy LSR introduces a Pad TLV to build the MPLS Echo Request packet,
   so in this case, the Proxy Ping Request MUST NOT include a Pad TLV.

   Any of following TLVs MAY be included.  These TLVs are used to form
   the MPLS Echo Request messages by the Proxy LSR:

      Pad

      Vendor Enterprise Number

      Reply TOS Byte

      P2MP Responder Identifier [RFC6425]

      Echo Jitter [RFC6425]

      Vendor Private TLVs

   Downstream Detailed Mapping (DDMAP) or Downstream Mapping (DSMAP)
   TLVs MAY be included.  These TLVs will be matched to the next-hop
   address for inclusion in those particular MPLS Echo Request messages.

   The message is then encapsulated in a UDP packet.  The source UDP
   port for the MPLS Proxy Ping Request message is chosen by the
   initiator; the destination UDP port is set to 3503.  The IP header is
   set as follows: the source IP address is a routable address of the
   initiator; the destination IP address is a routable address to the
   Proxy LSR.  The packet is then sent with the IP TTL set to 255.









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3.2.  Procedures for the Proxy LSR

   A Proxy LSR that receives an MPLS Proxy Ping Request message parses
   the packet to ensure that it is a well-formed packet.  It checks that
   the TLVs that are not marked "Ignore" are understood.  If any part of
   the message is malformed, it sets the Return Code to "Malformed echo
   request received".  If all the TLVs are well-formed and any TLVs are
   not understood, the Return Code is set to "TLV not understood".  The
   Return Subcode is set to zero for both cases.

   If the Reply Mode of the message header is not 1 ("Do not reply"), an
   MPLS Proxy Ping Reply message SHOULD be sent as described below.

   If the Return Code is "TLV not understood", no more processing of the
   MPLS Proxy Ping Request message is required.  The Proxy LSR sends an
   MPLS Proxy Ping Reply message with an Errored TLVs TLV containing
   (only) the TLVs that were not understood.

   The MPLS Proxy Ping Request is expected to be transported to the
   Proxy LSR via IP forwarding mechanisms instead of using the same
   techniques that are employed to inject an MPLS Echo Request packet
   into an LSP.  The MPLS Echo Request would use IP TTL, MPLS TTL,
   and/or loopback addresses (IPv4 127.x.x.x or IPv6 ::ffff:7f00/104) in
   the IP header destination address field to trigger the packet to be
   handled via an LSR's forwarding exception processing path.  The Proxy
   LSR MUST check whether or not MPLS Proxy Ping Request packets arrive
   via exception path.  Packets arriving via IP TTL expiry, IP
   destination address set to a loopback address, or label TTL expiry
   MUST be treated as "Unauthorized" packets.  An MPLS Proxy Ping Reply
   message MAY be sent with a Return Code of 16, "Proxy Ping not
   authorized".

   The header fields Sender's Handle and Sequence Number are not
   examined, but they are included in the MPLS Proxy Ping Reply or MPLS
   Echo Request message, if either is sent as a direct result of the
   received message.

   The Proxy LSR validates that it has a label mapping for the specified
   FEC, determines if it is an ingress, egress, transit or bud node, and
   then sets the Return Code as appropriate.  A new Return Code of 19,
   "Replying router has FEC mapping for topmost FEC", has been defined
   for the case where the Proxy LSR is an ingress (for example, the head
   of the TE tunnel or a transit router) because the existing Return
   Codes defined by RFC 4379 don't match the situation.  For example,
   when a Proxy LSR is a transit router, it's not appropriate for the
   Return Code to describe how the packet would transit because the MPLS





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   Proxy Ping Request doesn't contain information about what input
   interface the MPLS Echo Request would be switched from at the Proxy
   LSR.

   The Proxy LSR then determines if it is authorized to send the
   specified MPLS Echo Request on behalf of the initiator.  A Proxy LSR
   MUST be capable of filtering addresses to validate initiators.  Other
   filters on FECs or MPLS Echo Request contents MAY be applied.  If a
   configured filter has been invoked and an address does not pass the
   filter, then an MPLS Echo Request message MUST NOT be sent, and the
   event SHOULD be logged.  An MPLS Proxy Ping Reply message MAY be sent
   with a Return Code of 16, "Proxy Ping not authorized".

   The destination address specified in the Proxy Echo Parameters TLV is
   checked to ensure that it conforms to the allowed IPv4 or IPv6
   address range.  If not, the Return Code is set to "Malformed echo
   request received" and the Return Subcode is set to zero.  If the
   Reply Mode of the message header is not 1, an MPLS Proxy Ping Reply
   message SHOULD be sent as described below.

   The TTL specified in the Proxy Echo Parameters TLV is checked to
   ensure it contains a value in the range [1,255].  If not, the Return
   Code MUST be set to 17, "Proxy Ping parameters need to be modified".
   If the Reply Mode of the message header is not 1, an MPLS Proxy Ping
   Reply message SHOULD be sent as described below.

   If the "Request for FEC Neighbor Address info" flag is set, the
   Upstream Neighbor Address and Downstream Neighbor Address TLVs are
   formatted for inclusion in the MPLS Proxy Ping reply.  If the
   Upstream or Downstream address is unknown, the corresponding TLV is
   omitted.

   If there are Next Hop sub-TLVs in the Proxy Echo Parameters TLV, each
   address is examined to determine if it is a valid next hop for this
   FEC.  If any are not, the Proxy Echo Parameters TLV SHOULD be updated
   to remove unrecognized Next Hop sub-TLVs.  The updated Proxy Echo
   Parameters TLV MUST be included in the MPLS Proxy Ping Reply.

   If the "Request for Downstream Detailed Mapping" or "Request for
   Downstream Mapping" flag is set, the Proxy LSR formats (for inclusion
   in the MPLS Proxy Ping Reply) a DS/DDMAP TLV for each interface over
   which the MPLS Echo Request will be sent.

   If the Proxy LSR is the egress for the FEC, the behavior of the Proxy
   LSR varies depending on whether the LSR is an egress of a P2P LSP, a
   P2MP LSP, or MP2MP LSP.  Additional details can be found in Section
   3.2.1, "Proxy LSR Handling When It Is Egress for FEC".




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   If the Reply Mode of the MPLS Proxy Ping Request message header is 1
   ("Do not reply"), no MPLS Proxy Ping Reply is sent.  Otherwise, an
   MPLS Proxy Ping Reply message or MPLS Echo Request SHOULD be sent as
   described below.

3.2.1.  Proxy LSR Handling When It Is Egress for FEC

   This section describes the different behaviors for the Proxy LSR when
   it's the egress for the FEC.  In the P2MP bud node and MP2MP bud node
   egress cases, different behavior is required.

   In the case where an MPLS Echo Request is originated by an LSR that
   is a bud or egress node of a P2MP/MP2MP, MPLS Echo Replies are
   returned from downstream/upstream LSRs and will not include an MPLS
   Echo Reply from the LSR that originated the MPLS Echo Request.  This
   section describes the behavior required at a bud or egress node to
   return or not return information from MPLS Echo Replies in the Proxy
   Echo Reply so that no changes are required in implementations that
   are compliant with [RFC4379].  The Proxy Initiator should receive the
   same MPLS Echo Replies as in the case of the originator of the LSP
   Ping; any additional information (such as the Proxy LSR being a bud
   or egress node) is returned in the MPLS Proxy Ping Reply.

   When the Proxy LSR is the egress of a P2P FEC, an MPLS Proxy Ping
   Reply SHOULD be sent to the initiator with the Return Code set to 3,
   "Replying router is an egress for the FEC at stack-depth", with
   Return Subcode set to zero.

   When the Proxy LSR is the egress of a P2MP FEC, it can be either a
   bud node or just an egress.  If the Proxy LSR is a bud node, an MPLS
   Proxy Ping Reply SHOULD be sent to the initiator with the return code
   set to 3, "Replying router is an egress for the FEC at stack-depth",
   and Return Subcode set to zero.  DS/DDMAPs are included only if the
   Proxy Initiator requested information be returned in an MPLS Proxy
   Ping Reply.  If the Proxy LSR is a bud node but there has not been a
   request to return an MPLS Proxy Ping Reply, the Proxy LSR SHOULD send
   MPLS Echo Request packet(s) to the downstream neighbors (no MPLS Echo
   Reply is sent to the Proxy Initiator to indicate that the Proxy LSR
   is an egress).  If the Proxy LSR is just an egress, an MPLS Proxy
   Ping Reply SHOULD be sent to the initiator with the Return Code set
   to 3, "Replying router is an egress for the FEC at stack-depth", and
   Return Subcode set to zero.

   When the Proxy LSR is the egress of a MP2MP FEC, it can be either a
   bud node or just an egress.  LSP Pings sent from a leaf of a MP2MP
   have different behavior in this case.  MPLS Echo Requests are sent to
   all upstream/downstream neighbors.  The Proxy LSRs need to be
   consistent with this variation in behavior.  If the Proxy LSR is a



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   bud node or just an egress, an MPLS Proxy Ping Reply SHOULD be sent
   to the Proxy Initiator with the return code set to 3, "Replying
   router is an egress for the FEC at stack-depth", with Return Subcode
   set to zero and DS/DDMAPs included only if the Proxy Initiator
   requested information be returned in an MPLS Proxy Ping Reply.  If
   the Proxy LSR is not requested to return information in an MPLS Proxy
   Ping Reply, the Proxy LSR SHOULD send MPLS Echo Request packets to
   all upstream/downstream neighbors as would be done when sourcing an
   LSP Ping from a MP2MP leaf (no MPLS Echo Reply is sent to the Proxy
   Initiator indicating that the Proxy LSR is an egress).

3.2.2.  Downstream Detailed Maps and Downstream Maps in Proxy Reply

   When the Proxy LSR is a transit or bud node, downstream maps
   corresponding to how the packet is transited cannot be supplied
   unless an ingress interface for the MPLS Echo Request is specified.
   Since this information is not available and all valid output paths
   are of interest, the Proxy LSR SHOULD include DS/DDMAP(s) to describe
   the entire set of paths that the packet can be replicated.  This is
   similar to the case in which an LSP Ping is initiated at the Proxy
   LSR.  For mLDP, there is a DS/DDMAP per upstream/downstream neighbor
   for MP2MP LSPs, or per downstream neighbor in the P2MP LSP case.

   When the Proxy LSR is a bud node or egress in an MP2MP LSP or a bud
   node in a P2MP LSP, an LSP Ping initiated from the Proxy LSR would
   source packets only to the neighbors but not itself, despite the fact
   that the Proxy LSR is itself an egress for the FEC.  In order to
   match the behavior as seen from LSP Ping initiated at the Proxy LSR,
   the Proxy Reply SHOULD contain DS/DDMAPs for only the paths to the
   upstream/downstream neighbors, but no DS/DDMAP describing its own
   egress paths.  The proxy LSR identifies that it's an egress for the
   FEC using a different Proxy Reply Return Code.  The Proxy Reply
   Return Code is either set to 19, "Replying router has FEC mapping for
   topmost FEC", or 3, "Replying router is an egress for the FEC at
   stack-depth".

3.2.3.  Sending an MPLS Proxy Ping Reply

   The Reply Mode, Sender's Handle, and Sequence Number fields are
   copied from the Proxy Ping Request message.  The TLVs specified above
   are included.  The message is encapsulated in a UDP packet.  The
   source IP address is a routable address of the Proxy LSR; the source
   port is the well-known UDP port for LSP Ping.  The destination IP
   address and UDP port are copied from the source IP address and UDP
   port of the MPLS Proxy Ping Request.  The IP TTL is set to 255.






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3.2.4.  Sending the MPLS Echo Requests

   An MPLS Echo Request is formed as described in the next section.  The
   section below describes how the MPLS Echo Request is sent on each
   interface.

3.2.4.1.  Forming the Base MPLS Echo Request

   If Next Hop sub-TLVs were included in the received Proxy Echo
   Parameters TLV, the Next_Hop_List is created from the addresses in
   those sub-TLVs adjusted as described in Section 3.2.  Otherwise, the
   list is set to all the next hops to which the FEC would be forwarded.

   The Proxy LSR then formats an MPLS Echo Request message.  The Global
   Flags and Reply Mode are copied from the Proxy Echo Parameters TLV.
   The Return Code and Return Subcode are set to zero.

   The Sender's Handle and Sequence Number are copied from the remote
   MPLS Echo Request message.

   The TimeStamp Sent is set to the time of day (in seconds and
   microseconds) that the MPLS Echo Request is sent.  The TimeStamp
   Received is set to zero.

   If the Reply-to Address TLV is present, it is used to set the MPLS
   Echo Request source address; otherwise, the MPLS Echo Request source
   address is set to the Proxy Request source address.

   The following TLVs are copied from the MPLS Proxy Ping Request
   message.  Note that, of these, only the Target FEC Stack is REQUIRED
   to appear in the MPLS Proxy Ping Request message.  The Pad TLV is not
   copied if the Proxy Echo Parameter TLV MPLS payload size is set to a
   non-zero value.

      Target FEC Stack

      Pad

      Vendor Enterprise Number

      Reply TOS Byte

      P2MP Responder Identifier [RFC6425]

      Echo Jitter [RFC6425]

      Vendor Private TLVs




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   If the Proxy Echo Parameter TLV MPLS payload size is non-zero, the
   Proxy LSR introduces a Pad TLV such that size of the MPLS Echo
   Request (including any IP and UDP header) is zero-padded to the
   specified MPLS payload size.  The first octet in the Value part of
   the Pad TLV is set to 1, "Drop Pad TLV from reply", and the remaining
   octets of the Value part of the Pad TLV are filled with zeros.  If
   the IP header is used to encapsulate the MPLS Echo Request, the DF
   bit MUST be set to one.

   The message is then encapsulated in a UDP packet.  The source UDP
   port is copied from the Proxy Echo Parameters TLV.  The destination
   port is copied from the MPLS Proxy Ping Request message.

   The source IP address is set to a routable address specified in the
   Reply-to Address TLV or the source address of the received Proxy
   Request.  Per usual, the TTL of the IP packet is set to 1.

   If the Explicit Differentiated Services Code Point (DSCP) flag is
   set, the Requested DSCP byte is examined.  If the setting is
   permitted, then the DSCP byte of the IP header of the MPLS Echo
   Request message is set to that value.  If the Proxy LSR does not
   permit explicit control for the DSCP byte, the MPLS Proxy Echo
   Parameters with the Explicit DSCP flag cleared MUST be included in
   any MPLS Proxy Ping Reply message to indicate why an MPLS Echo
   Request was not sent.  The Return Code MUST be set to 17, "Proxy Ping
   parameters need to be modified".  If the Explicit DSCP flag is not
   set, the Proxy LSR SHOULD set the MPLS Echo Request DSCP settings to
   the value normally used to source LSP Ping packets.

3.2.4.2.  Per-Interface Sending Procedures

   The Proxy LSR now iterates through the Next_Hop_List modifying the
   base MPLS Echo Request to form the MPLS Echo Request packet that is
   then sent on that particular interface.

   The outgoing label stack is determined for each next-hop address.
   The TTL for the label corresponding to the FEC specified in the FEC
   stack is set such that the TTL on the wire will be the TTL specified
   in the Proxy Echo Parameters.  If any additional labels are pushed
   onto the stack, their TTLs are set to 255.  This will ensure that the
   requestor will not have control over tunnels not relevant to the FEC
   being tested.









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   If the MPLS Proxy Ping Request message contained Downstream Mapping
   TLVs or Downstream Detailed Mapping TLVs, they are examined.  If the
   Downstream IP address matches the next-hop address, that Downstream
   Mapping TLV is included in the MPLS Echo Request.

   The packet is then transmitted on this interface.

4.  Proxy Ping Request/Reply Messages

   This document defines two new LSP Ping messages, the MPLS Proxy Ping
   Request and the MPLS Proxy Ping Reply.

4.1.  Proxy Ping Request/Reply Message Formats

   The packet format is as defined in [RFC4379].  Two new message types,
   Proxy Ping Request and Reply, are being added.

   Message Type

   Type    Message
   ----    -------
      3    MPLS Proxy Ping Request
      4    MPLS Proxy Ping Reply

4.2.  Proxy Ping Request Message Contents

   The MPLS Proxy Ping Request message MAY contain the following
   TLVs:

          Type    TLV
          ----    -----------
             1    Target FEC Stack
             2    Downstream Mapping (DEPRECATED)
             3    Pad
             5    Vendor Enterprise Number
            10    Reply TOS Byte
            11    P2MP Responder Identifier [RFC6425]
            12    Echo Jitter [RFC6425]
            20    Downstream Detailed Mapping
            21    Reply Path [RFC7110]
            22    Reply TC [RFC7110]
            23    Proxy Echo Parameters
            24    Reply-to Address
             *    Vendor Private TLVs

         * TLVs types in the Vendor Private TLV Space MUST be ignored if
           not understood




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4.3.  Proxy Ping Reply Message Contents

   The MPLS Proxy Ping Reply message MAY contain the following TLVs:

          Type    TLV
          ----    -----------
             1    Target FEC Stack
             2    Downstream Mapping (DEPRECATED)
             5    Vendor Enterprise Number
             9    Errored TLVs
            20    Downstream Detailed Mapping
            23    Proxy Echo Parameters
            25    Upstream Neighbor Address
            26    Downstream Neighbor Address (0 or more)
             *    Vendor Private TLVs

         * TLVs types in the Vendor Private TLV Space MUST be ignored if
           not understood

5.  TLV Formats

5.1.  Proxy Echo Parameters TLV

   The Proxy Echo Parameters TLV is a TLV that MUST be included in an
   MPLS Proxy Ping Request message.  The length of the TLV is 12 + K +
   S, where K is the length of the Destination IP Address field and S is
   the total length of the sub-TLVs.  The Proxy Echo Parameters TLV can
   be used either to 1) control attributes used in composing and sending
   an MPLS Echo Request or 2) query the Proxy LSR for information about
   the topmost FEC in the target FEC stack, but not both.  In the case
   where the Proxy LSR is being queried (i.e., information needs to be
   returned in an MPLS Proxy Ping Reply), no MPLS Echo Request will be
   sent from the Proxy LSR.  The MPLS Proxy Ping Request Proxy Echo
   Parameters TLV's Proxy Flags SHOULD be set appropriately, as
   described below.
















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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Address Type |   Reply Mode  |        Proxy Flags            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      TTL      |  Rqst'd DSCP  |        Source UDP Port        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Global Flags         |       MPLS Payload Size       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   :                      Destination IP Address                   :
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   :                                                               :
   :                            Sub-TLVs                           :
   :                                                               :
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Address Type

      The type and length of the address found in the in the Destination
      IP Address and Next Hop IP Addresses fields.  The values are
      shared with the Downstream Mapping Address Type Registry.

      The type codes applicable in this case appear in the table below:

           Address Family   Type     Length

                IPv4          1         4
                IPv6          3        16

   Reply Mode

      The reply mode to be sent in the MPLS Echo Request message; the
      values are as specified in [RFC4379].

   Proxy Flags

      The Proxy Request Initiator sets zero, one, or more of these flags
      to request actions at the Proxy LSR.

         0x0001 Request for FEC Neighbor Address info

            When set, this requests that the Proxy LSR supply the
            Upstream and Downstream neighbor address information in the
            MPLS Proxy Ping Reply message.  This flag is only applicable



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            for the topmost FEC in the FEC stack if the FEC type
            corresponds with a P2MP or MP2MP LSP.  The Proxy LSR MUST
            respond (as applicable) with Upstream Neighbor Address and
            Downstream Neighbor Address TLV(s) in the MPLS Proxy Ping
            Reply message.  The Upstream Neighbor Address TLV needs be
            included only if there is an upstream neighbor.  Similarly,
            one Downstream Neighbor Address TLV needs to be included for
            each Downstream Neighbor from which the LSR learned
            bindings.

            Setting this flag will cause the Proxy LSR to cancel sending
            any MPLS Echo Request.  The initiator may use information
            learned from the MPLS Proxy Ping Reply that is sent instead
            to generate subsequent proxy requests.

         0x0002 Request for Downstream Mapping

            When set, this requests that the Proxy LSR supply a
            Downstream Mapping TLV (see [RFC4379]) in the MPLS Proxy
            Ping Reply message.  Either this flag may be set or the
            "Request for Downstream Detailed Mapping" flag may be set,
            but not both.

            Setting this flag will cause the Proxy LSR to cancel sending
            an MPLS Echo Request.  Information learned with such a Proxy
            Reply may be used by the Proxy Initiator to generate
            subsequent Proxy Requests.

         0x0004 Request for Downstream Detailed Mapping

            When set, this requests that the Proxy LSR supply a
            Downstream Detailed Mapping TLV (see [RFC6424]) in the MPLS
            Proxy Ping Reply message.  It's not valid to have the
            "Request for Downstream Mapping" flag set when this flag is
            set.  Setting this flag will cause the Proxy LSR to cancel
            sending an MPLS Echo Request.  The initiator may use
            information learned from the MPLS Proxy Ping Reply that is
            sent instead to generate subsequent proxy requests.

         0x0008 Explicit DSCP Request

            When set, this requests that the Proxy LSR use the supplied
            "Rqst'd DSCP" byte in the Echo Request message








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      TTL

         The TTL to be used in the label stack entry corresponding to
         the topmost FEC in the MPLS Echo Request packet.  Valid values
         are in the range [1,255].

      Requested DSCP

         This field is valid only if the Explicit DSCP flag is set.  If
         not set, the field MUST be zero on transmission and ignored on
         receipt.  When the flag is set, this field contains the DSCP
         value to be used in the MPLS Echo Request packet IP header.

      Source UDP Port

         The source UDP port to be sent in the MPLS Echo Request packet

      Global Flags

         The Global Flags to be sent in the MPLS Echo Request message

      MPLS Payload Size

         Used to request that the MPLS payload (IP header + UDP header +
         MPLS Echo Request) be padded using a zero-filled Pad TLV so
         that the IP header, UDP header, and MPLS Echo Request total the
         specified size.  Having the field set to zero means no size
         request is being made.  If the requested size is less than the
         minimum size required to form the MPLS Echo Request, the
         request will be treated as a best-effort request with the Proxy
         LSR building the smallest possible packet (i.e., not using a
         Pad TLV).  The IP header DF bit MUST be set when this field is
         non-zero.

      Destination IP Address

         If the Address Type is IPv4, an address from the range 127/8;
         if the Address Type is IPv6, an address from the range
         ::ffff:7f00:0/104

      Sub-TLVs

         List of TLV-encoded sub-TLVs.  Currently one is defined.

          Sub-Type       Length            Sub-TLV Name
          --------       ------            ------------
                 1         8+              Next Hop




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5.1.1.  Next Hop Sub-TLV

   This sub-TLV is used to describe a particular next hop towards which
   the Echo Request packet should be sent.  If the topmost FEC in the
   FEC stack is a multipoint LSP, this sub-TLV may appear multiple
   times.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Addr Type   |                      MBZ                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Next Hop IP Address (4 or 16 octets)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Next Hop Interface  (0, 4, or 16 octets)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Address Type

           Type     Type of Next Hop   Addr Length  Interface Field (IF)
                                                          Length
             1        IPv4 Numbered           4             4
             2        IPv4 Unnumbered         4             4
             3        IPv6 Numbered          16            16
             4        IPv6 Unnumbered        16             4
             5        Reserved
             6        IPv4 Protocol Adj       4             0
             7        IPv6 Protocol Adj      16             0

         Note:  Types 1-4 correspond to the types in the DSMAP TLV.
                They are expected to be populated with information
                obtained through a previously returned DSMAP TLV.  Types
                6 and 7 are intended to be populated from the local
                address information obtained from a previously returned
                Downstream Neighbor Address TLV or Upstream Neighbor
                Address TLV.

       Next Hop IP Address

         A next hop address that the Echo Request message is to be sent
         towards

       Next Hop Interface

         Identifier of the interface through which the Echo Request
         message is to be sent.  For Addr Type 5 and 6, the Next Hop
         interface field isn't used and MUST be of an associated byte
         length of zero octets.



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5.2.  Reply-to Address TLV

   Used to specify the MPLS Echo Request IP source address.  This
   address MUST be IP reachable via the Proxy LSR; otherwise, it will be
   rejected.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Address Type |                      MBZ                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   :                       Reply-to Address                        :
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Address Type

         A type code as specified in the table below:

            Type     Type of Address

              1        IPv4
              3        IPv6

5.3.  Upstream Neighbor Address TLV

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Upst Addr Type |Local Addr Type|             MBZ               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   :                     Upstream Address                          :
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   :                         Local Address                         :
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Upst Addr Type; Local Addr Type

         These two fields determine the type and length of the
         respective addresses.  The codes are specified in the table
         below:





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           Type     Type of Address          Length

             0        No Address Supplied       0
             1        IPv4                      4
             3        IPv6                     16

       Upstream Address

         The address of the immediate upstream neighbor for the topmost
         FEC in the FEC stack.  If the protocol adjacency exists by
         which the label for this FEC was exchanged, this address MUST
         be the address used in that protocol exchange.

       Local Address

         The local address used in the protocol adjacency by which the
         label for this FEC was exchanged.

5.4.  Downstream Neighbor Address TLV

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Dnst Addr Type |Local Addr Type|             MBZ               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   :                     Downstream Address                        :
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   :                         Local Address                         :
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Dnst Addr Type; Local Addr Type

         These two fields determine the type and length of the
         respective addresses.  The codes are specified in the table
         below:

            Type     Type of Address          Length

              0        No Address Supplied       0
              1        IPv4                      4
              3        IPv6                     16






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       Downstream Address

         The address of an immediate downstream neighbor for the topmost
         FEC in the FEC stack.  If the protocol adjacency exists by
         which the label for this FEC was exchanged, this address MUST
         be the address used in that protocol exchange.

       Local Address

         The local address used in the protocol adjacency by which the
         label for this FEC was exchanged.

6.  Security Considerations

   The mechanisms described in this document are intended to be used
   within a service provider network and to be initiated only under the
   authority of that administration.

   If such a network also carries Internet traffic, or permits IP access
   from other administrations, the MPLS Proxy Ping message SHOULD be
   discarded at the points where IP packets are received from other
   administrations.  This can be accomplished by filtering on source
   address or by filtering all MPLS ping messages on UDP port.

   Any node that acts as a Proxy LSR SHOULD validate requests against a
   set of valid source addresses.  An implementation MUST provide such
   filtering capabilities.

   MPLS Proxy Ping Request messages are IP addressed directly to the
   Proxy LSR.  If a Proxy LSR receives an MPLS Proxy Ping message via
   expiration of the IP or Label Stack Entry TTL, it MUST NOT be acted
   upon.

   If an MPLS Proxy Ping Request IP source address is not IP reachable
   by the Proxy LSR, the Proxy Request MUST NOT be acted upon.

   MPLS Proxy Ping Requests are limited to making their request via the
   specification of a FEC.  This ensures that only valid MPLS Echo
   Request messages can be created.  No label-spoofing attacks are
   possible.











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7.  IANA Considerations

   Per this document, IANA has made the following assignments.

   MPLS LSP Ping Message Types

        Value      Meaning
        -----      -------
            3      MPLS Proxy Ping Request
            4      MPLS Proxy Ping Reply

   TLVs

         Type      TLV Name
         ----      --------
           23      Proxy Echo Parameters
           24      Reply-to Address
           25      Upstream Neighbor Address
           26      Downstream Neighbor Address


   Return Codes

        Value      Meaning
        -----      -------
           16      Proxy Ping not authorized
           17      Proxy Ping parameters need to be modified
           18      MPLS Echo Request could not be sent
           19      Replying router has FEC mapping for topmost FEC

7.1.  Proxy Echo Parameters Sub-TLVs

   The IANA has created and maintains this new registry for Proxy Echo
   Parameters Sub-TLVs.  Assignments will use the same rules spelled out
   in Section 7.2 of [RFC4379].

         Sub-Type     Sub-TLV Name
         --------     ------------
            0         Reserved
            1         Next Hop











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7.2.  Proxy Flags

   IANA has created and maintains a new registry for the Proxy Flags
   that are used with the Proxy Echo Parameters TLV.  See Section 5.1
   for details.  The registry is in the "Multi-Protocol Label Switching
   (MPLS) Label Switched Paths (LSPs) Ping Parameters" registry in the
   "Multiprotocol Label Switching Architecture (MPLS)" name space.  The
   registration procedure is Standards Action [RFC5226].  The initial
   values are as follows.

         Bit Number     Name
         ----------     ----
             0          Request for FEC Neighbor Address info
             1          Request for Downstream Mapping
             2          Request for Downstream Detailed Mapping
             3          Explicit DSCP Request
             4-15       Unassigned

7.3.  Downstream Address Mapping Registry

   This document makes the following assignments in the Downstream
   Address Mapping Registry.  This document updates the registry defined
   by [RFC6426].  The registration procedure remains Standards Action
   and a note has been added as follows:

      When a code point is assigned that is not also assigned in the
      Next Hop Address Type Registry, the code point there must be
      marked "Reserved".

   Type #      Address Type         K Octets
   ------      ------------         --------
        6      Reserved             N/A       RFC 7555
        7      Reserved             N/A       RFC 7555

7.4.  Next Hop Sub-TLV Address Type Registry

   IANA has created a new registry called the "Next Hop Address Type
   Registry".  The allocation policy for this registry is Standards
   Action.  Further, a note has been added as follows:

      When a code point is assigned that is not also assigned in the
      Downstream Address Mapping Registry, the code point there must be
      marked "Reserved".








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   The initial allocations are:

      Type     Type of Next Hop   Addr Length  IF Length   Reference

      1        IPv4 Numbered           4          4        [RFC4379]
      2        IPv4 Unnumbered         4          4        [RFC4379]
      3        IPv6 Numbered          16         16        [RFC4379]
      4        IPv6 Unnumbered        16          4        [RFC4379]
      5        Reserved                                     RFC 7555
      6        IPv4 Protocol Adj       4          0         RFC 7555
      7        IPv6 Protocol Adj      16          0         RFC 7555
      8-255    Unassigned

8.  References

8.1.  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>.

   [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,
              <http://www.rfc-editor.org/info/rfc6425>.

   [RFC6426]  Gray, E., Bahadur, N., Boutros, S., and R. Aggarwal, "MPLS
              On-Demand Connectivity Verification and Route Tracing",
              RFC 6426, DOI 10.17487/RFC6426, November 2011,
              <http://www.rfc-editor.org/info/rfc6426>.

   [RFC7110]  Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord,
              "Return Path Specified Label Switched Path (LSP) Ping",
              RFC 7110, DOI 10.17487/RFC7110, January 2014,
              <http://www.rfc-editor.org/info/rfc7110>.




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8.2.  Informative References

   [RFC4875]  Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
              Yasukawa, Ed., "Extensions to Resource Reservation
              Protocol - Traffic Engineering (RSVP-TE) for Point-to-
              Multipoint TE Label Switched Paths (LSPs)", RFC 4875,
              DOI 10.17487/RFC4875, May 2007,
              <http://www.rfc-editor.org/info/rfc4875>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC6388]  Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.
              Thomas, "Label Distribution Protocol Extensions for Point-
              to-Multipoint and Multipoint-to-Multipoint Label Switched
              Paths", RFC 6388, DOI 10.17487/RFC6388, November 2011,
              <http://www.rfc-editor.org/info/rfc6388>.

Acknowledgements

   The authors would like to thank Nobo Akiya, Adrian Farrel, Tom Yu,
   Tom Taylor, and Warren Kumari for their detailed reviews and
   insightful comments.


























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Authors' Addresses

   George Swallow
   Cisco Systems
   1414 Massachusetts Ave
   Boxborough, MA  01719
   United States

   EMail: swallow@cisco.com


   Vanson Lim
   Cisco Systems
   1414 Massachusetts Avenue
   Boxborough, MA  01719
   United States

   EMail: vlim@cisco.com


   Sam Aldrin
   Huawei Technologies
   2330 Central Express Way
   Santa Clara, CA  95951
   United States

   EMail: aldrin.ietf@gmail.com
























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