Proxy MPLS Echo Request
draft-ietf-mpls-proxy-lsp-ping-04

Network Working Group                                         G. Swallow
Internet-Draft                                                    V. Lim
Intended status: Standards Track                           Cisco Systems
Expires: August 30, 2015                                       S. Aldrin
                                                     Huawei Technologies
                                                       February 26, 2015

                        Proxy MPLS Echo Request
                   draft-ietf-mpls-proxy-lsp-ping-04

Abstract

   This document defines a means of remotely initiating Multiprotocol
   Label Switched Protocol 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 leaf to
   leaf/root tracing.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 30, 2015.

 

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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
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   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.  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 . . . . . . . . . . . . . . .  8
       3.2.1.  Proxy LSR Handling when it is egress for FEC . . . . . 10
       3.2.2.  Downstream Detailed/Downstream Maps in Proxy Reply . . 11
       3.2.3.  Sending an MPLS Proxy Ping Reply . . . . . . . . . . . 12
       3.2.4.  Sending the MPLS Echo Requests . . . . . . . . . . . . 12
         3.2.4.1.  Forming the base MPLS Echo Request . . . . . . . . 12
         3.2.4.2.  Per interface sending procedures . . . . . . . . . 14
   4.  Proxy Ping Request / Reply Messages  . . . . . . . . . . . . . 14
     4.1.  Proxy Ping Request / Reply Message formats . . . . . . . . 14
     4.2.  Proxy Ping Request Message contents  . . . . . . . . . . . 14
     4.3.  Proxy Ping Reply Message Contents  . . . . . . . . . . . . 15
   5.  TLV formats  . . . . . . . . . . . . . . . . . . . . . . . . . 15
     5.1.  Proxy Echo Parameters TLV  . . . . . . . . . . . . . . . . 15
       5.1.1.  Next Hop sub-TLV . . . . . . . . . . . . . . . . . . . 19
     5.2.  Reply-to Address TLV . . . . . . . . . . . . . . . . . . . 20
     5.3.  Upstream Neighbor Address TLV  . . . . . . . . . . . . . . 20
     5.4.  Downstream Neighbor Address TLV  . . . . . . . . . . . . . 21
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 22
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22
     8.1.  Proxy Echo Parameters Sub-TLVs . . . . . . . . . . . . . . 23
 

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   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 24
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24

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
   Label Distribution Protocol based Point-to-Multipoint (P2MP) and
   Multipoint-to-Multipoint (MP2MP) Label Switched Paths [RFC6388], is
   the ability to trace a sub-LSP from leaf node to root node.

   It is anticipated that very large Point-to-Multipoint and Multipoint-
   to-Multipoint (MP2MP) Label Switched Paths will exist. Further 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 which 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 working 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 both 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
 

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   initiate a trace. First the above procedure is 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 [RFC6388].

   While the motivation for this document came from multicast scaling
   concerns, it's 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 sent out of band of the LSP over IP. Remote pinging of LSPs that
   involve 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 does it 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.

   Based on context the terms leaf and egress are used interchangeably.
   Egress is used where consistency with[RFC4379] was deemed
 

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   appropriate. Receiver is used in the context of receiving protocol
   messages.

1.2.  Terminology

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

   [Note (to be removed after assignments occur): <TBA> = to be assigned
   by IANA]

2.  Proxy Ping Overview

   This document defines a protocol interaction between a first node, a
   node which is part of an LSP, to allow the first node to request that
   the second node initiate an LSP ping for the LSP on the first node's
   behalf. Since the second node sends the LSP Ping on behalf of the
   first node, 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 node or another
   node 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 nodes with the following terms:

      Initiator - the node which initiates the ping operation by sending
      an MPLS Proxy Ping Request message

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

      Receiver(s) - the nodes which receive the MPLS Echo Request
      message

 

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

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

2.1.  Initiating Proxy Ping

   The initiator formats an MPLS Proxy Ping Request message and sends it
   to the Proxy LSR, a node it believes to be on the path of the LSP.
   This message instructs the Proxy LSR to either Reply with Proxy
   information or to send an MPLS Echo Request inband 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 nodes along the LSP.

2.2.  Handling at Proxy LSR

   The Proxy LSR either replies with the requested Proxy information or
   it 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 to be
   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 it inband 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 sec 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 Subcode to zero. If
   there are any TLVs not marked as "Ignore" that Proxy LSR does not
   understand, Proxy LSR SHOULD send an MPLS "TLV not understood" (as
 

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   appropriate), and the Subcode set to zero.

   In the case where the targeted Proxy LSR does not understand the LSP
   ping Echo Request at all, like any other LSR which does not
   understand the messages, it MUST drop them 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 lookup 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 in
   the MPLS Echo Request packet. If the Address Type is IPv4, an address
   is from the range 127/8. If the Address Type is IPv6, an address is
   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 a node 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 or Downstream Mapping TLV is required in an
   MPLS Proxy Ping Reply, the initiator sets the "Request for Downstream
   Detailed Mapping" or "Request for Downstream Mapping" Proxy Flags 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.

   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
 

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   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 LSPs
   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 TLV [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 User
   Datagram Protocol (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.

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
 

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   not understood, the Return Code is set to "TLV not understood". The
   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 all
   the not understood TLVs (only).

   The Proxy LSR checks that the MPLS Proxy Ping Request message did not
   arrive via one of its exception processing paths. Packets arriving
   via IP TTL expiry, IP destination address set to a Martian 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 <TBA-7>,
   "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, it then determines if it is an ingress, egress, transit or bud
   node and sets the Return Code as appropriate. A new Return Code of
   <TBA-10>, "Replying router has FEC mapping for topmost FEC" has been
   defined for the case where the Proxy LSR is an ingress (for example
   head of the TE tunnel or a transit router) because the existing
   RFC4379 Return Codes 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 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 <TBA-7>, "Proxy Ping not authorized".

   The destination address specified in the Proxy Echo Parameters TLV is
   checked to ensure that it conforms to the address allowed IPv4 or
   IPv6 address range. If not, the Return Code set to "Malformed echo
   request received" and the Subcode set to zero. If the Reply Mode of
 

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   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, Proxy Echo Parameters TLV SHOULD be updated
   removing 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 Downstream Detailed/Downstream
   Mapping (DD/DSMAP) 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 node is an egress of a P2P LSP, a
   P2MP LSP or MP2MP LSP. Additional details can be found in the section
   describing "Handling when Proxy LSR it is egress for FEC".

   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 budnode and MP2MP budnode
   and egress cases, different behavior is required.

   In the case where an LSP ping is originated from P2MP/MP2MP bud
   node/egress, MPLS Echo Replies are returned from downstream/upstream
   routers and won't include an MPLS Echo Reply from the node that
   originated the MPLS Echo Requests. This section describes the
   behavior required at the bud/egress node to return information not
   returned by MPLS Echo Replies in the Proxy Echo Reply so that there
   is no additional changes required in the [RFC4379] implementations.
   The Proxy Initiator should receive the same MPLS Echo Replies as in
   the case where of the originator of the LSP ping, any additional
   information such as the Proxy LSR being a bud node/egress is returned
   in the MPLS Proxy Ping Reply. 

 

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   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,
   "Reply router is egress for FEC", with Return Subcode set to 0.

   When the Proxy LSR is the egress of a P2MP FEC, it can be either a
   budnode or just an egress. If the Proxy LSR is a budnode, an MPLS
   Proxy Ping Reply SHOULD be sent to the initiator with the Return Code
   set to 3, "Reply router is egress for FEC", with Return Subcode set
   to 0 and DS/DDMAPs only if the Proxy initiator requested information
   to be returned in an MPLS Proxy Ping Reply. If the Proxy LSR is a
   budnode but not requested 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, "Reply router is egress for FEC", and
   Return Subcode set to 0. 

   When the Proxy LSR is the egress of a MP2MP FEC, it can be either a
   budnode 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 budnode or
   just an egress, an MPLS proxy ping reply SHOULD be sent to the Proxy
   Initiator with the return code set to 3, "Reply router is Egress for
   FEC", with Return Subcode set to 0 and DS/DDMAPs included only if the
   Proxy initiator requested information to be returned in a 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/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 DSMAP/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
 

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   budnode 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 DSMAP/DDMAPs for only the paths to the
   upstream/downstream neighbors, but no DSMAP/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 "Reply router has a mapping for the topmost
   FEC" or "Reply router is egress for the FEC".

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.

3.2.4.  Sending the MPLS Echo Requests

   An MPLS Echo Request is formed as described in the next section. The
   section below that 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
   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 echo
   request source address; otherwise the echo request source address is
   set to the Proxy Request source address.
 

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   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 TLV [RFC6425]

      Vendor Private TLVs

   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 Value part of the
   Pad TLV is set to 1, "Drop Pad TLV from Reply", the remaining Octets
   of the Value part of the Pad TLV is filled with zeros.  If IP header
   is use to encapsulate in 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 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 <TBA-8>, "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..
 

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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 which 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 other 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.

   If the MPLS Proxy Ping Request message contained Downstream Mapping/
   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
   ----     -------
   TBA-1    MPLS Proxy Ping Request
            (Pending IANA assignment)

   TBA-2    MPLS Proxy Ping Reply
            (Pending IANA assignment)

4.2.  Proxy Ping Request Message contents

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

          Type    TLV
          ----    -----------
 

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             1    Target FEC Stack
             2    Downstream Mapping
             3    Pad
             5    Vendor Enterprise Number
            10    Reply TOS Byte

            11    P2MP Responder Identifier [RFC6425]
            12    Echo Jitter TLV [RFC6425]
            20    Downstream Detailed Mapping
            21    Reply Path [RFC7110]
            22    Reply TC [RFC7110]
         TBA-3    Proxy Echo Parameters (Pending IANA assignment)
         TBA-4    Reply-to-Address TLV
             *    Vendor Private TLVs

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

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
             5    Vendor Enterprise Number
             9    Errored TLVs
            20    Downstream Detailed Mapping
         TBA-3    Proxy Echo Parameters (Pending IANA assignment)
         TBA-5    Upstream Neighbor Address (Pending IANA assignment)
         TBA-6    Downstream Neighbor Address (0 or more)
                  (Pending IANA assignment)
             *    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
 

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   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 echo header's
   Reply Mode SHOULD be set to "Reply with Proxy Info".

    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
 

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

         0x01 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
            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.

         0x02 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 Echo request. Information learned with such Proxy Reply
            may be used by the Proxy initiator to generate subsequent
            Proxy Requests.

         0x04 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 Request for
            Downstream Mapping flag set when this flag is set. Setting
            this flag will cause the Proxy LSR to cancel sending an Echo
            request. The initiator may use information learned from the
            MPLS proxy ping reply that is sent instead to generate
            subsequent proxy requests.

         0x08 Explicit DSCP Request
 

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

      TTL

         The TTL to be used in the label stack entry corresponding to
         the topmost FEC in the in the MPLS Echo Request packet. Valid
         values are in the range [1,255]. A setting of 0 SHOULD be
         ignored by the Proxy LSR.

      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. 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-TLV Type       Length            Value Field
 

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          ------------       ------            -----------
          <TBA-13>             8+               Next Hop

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   |                  MUST be Zero                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              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  IF Length

              1        IPv4 Numbered           4          4
              2        IPv4 Unnumbered         4          4
              3        IPv6 Numbered          16         16
              4        IPv6 Unnumbered        16          4
              TBA-11   IPv4 Protocol Adj       4          0
              TBA-12   IPv6 Protocol Adj      16          0

       Note:  Types 1-4 correspond to the types in the DS Mapping TLV.
              They are expected to populated with information obtained
              through a previously returned DS Mapping TLV. Types
              <TBA-11> and <TBA-12> are intended to be populated
              from the local address information obtained from a
              previously returned Downstream Neighbor Address
              TLV(s)/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
 

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         interface field isn't used and MUST be of an associated byte
         length of "0" octets.

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 |               MUST be Zero                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   :                       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|       MUST be Zero            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   :                     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
 

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         below:

           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 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 exists 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|       MUST be Zero            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   :                     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 a immediate downstream neighbor for the topmost
         FEC in the FEC stack. If 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 exists 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, MPLS proxy ping message SHOULD be
   discarded at the points that where the IP packet is received from the
   other administration. This can be accomplished by filtering on source
   address or by filtering all MPLS ping messages on UDP port.

   Any node which acts as a Proxy node 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 node. If a node receives an MPLS Proxy Ping message via IP or
   Label TTL expiration, 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.

7.  Acknowledgements

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

8.  IANA Considerations

 

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   This document makes the following assignments (pending IANA action)

   MPLS LSP Ping Message Types

         Type       Value Field
         ----       -----------
         TBA-1      MPLS Proxy Ping Request
         TBA-2      MPLS Proxy Ping Reply

   TLVs

         Type       Value Field
         ----       -----------
         TBA-3      Proxy Echo Parameters
         TBA-4      Reply-to Address
         TBA-5      Upstream Neighbor Address
         TBA-6      Downstream Neighbor Address

   Return Code [pending IANA assignment]

        Value       Meaning
        -----       -------
        TBA-7       Proxy Ping not authorized.
        TBA-8       Proxy Ping parameters need to be modified.
        TBA-9       MPLS Echo Request Could not be sent.
        TBA-10      Replying router has FEC mapping for topmost FEC.

   Downstream Address Mapping Registry [pending IANA assignment]

        Value       Meaning
        -----       -------
        TBA-11      IPv4 Protocol Adj
        TBA-12      IPv6 Protocol Adj

8.1.  Proxy Echo Parameters Sub-TLVs

   The IANA will create and maintain this new registry for Proxy Echo
   Parameters Sub-TLV's. Assignments will use the same rules spelled out
   in sec 7.2 of [RFC4379].

         Sub-TLV Type    Meaning
         -----------     -------
         0               Reserved
         TBA-13          Next Hop

 

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9.  References

9.1.  Normative References

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

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

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

   [RFC6425]  Saxena, S., 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, November 2011.

   [RFC7110]  Chen, M., Cao, W., Ning, S., Jounay, F., and Delord, S.,
              "Return Path Specified Label Switched Path (LSP) Ping",
              RFC 7110, January 2014.

9.2.  Informative References

   [RFC4875]  Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
              "Extensions to Resource Reservation Protocol - Traffic
              Engineering (RSVP-TE) for Point-to-Multipoint TE Label
              Switched Paths (LSPs)", RFC 4875, May 2007.

   [RFC6388]  Wijnands, IJ., Minei, I., Kompella, K., and B. Thomas,
              "Label Distribution Protocol Extensions for Point-to-
              Multipoint and Multipoint-to-Multipoint Label Switched
              Paths", RFC 6388, November 2011.

Authors' Addresses

   George Swallow
   Cisco Systems
   1414 Massachusetts Ave
   Boxborough, MA  01719
   USA

   Email: swallow@cisco.com

 

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   Vanson Lim
   Cisco Systems
   1414 Massachusetts Avenue
   Boxborough, MA  01719
   USA

   Email: vlim@cisco.com

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

   Email: aldrin.ietf@gmail.com

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