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Versions: (draft-zj-mpls-lsp-ping-reply-relay) 00 01 draft-ietf-mpls-lsp-ping-relay-reply

Network Working Group                                      R. Zheng, Ed.
Internet-Draft                                               L. Jin, Ed.
Updates: 4379 (if approved)                                          ZTE
Intended status: Standards Track                          T. Nadeau, Ed.
Expires: August 5, 2013                                 Juniper Networks
                                                         G. Swallow, Ed.
                                                                   Cisco
                                                        February 1, 2013


               Relayed Echo Reply mechanism for LSP Ping
                draft-zjns-mpls-lsp-ping-relay-reply-01

Abstract

   In some inter-AS and inter-area deployment scenarios for LSP Ping and
   Traceroute, a replying LSR may not have the available route to the
   initiator, and the Echo Reply message sent to the initiator would be
   discarded resulting in false negatives or complete failure of
   operation of LSP Ping and Traceroute.  This document describes
   extensions to LSP Ping mechanism to enable the replying LSR to have
   the capability to relay the echo response by a set of routable
   intermediate nodes to the initiator during the traceroute process in
   inter-AS and inter-area scenarios.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 5, 2013.

Copyright Notice

   Copyright (c) 2013 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



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


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Conventions Used in This Document  . . . . . . . . . . . .  3
   2.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Extensions . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Relayed Echo Reply message . . . . . . . . . . . . . . . .  5
     3.2.  Relay Node Address Stack . . . . . . . . . . . . . . . . .  6
     3.3.  New Return Code  . . . . . . . . . . . . . . . . . . . . .  7
   4.  Procedures . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Sending an Echo Request  . . . . . . . . . . . . . . . . .  8
     4.2.  Receiving an Echo Request  . . . . . . . . . . . . . . . .  8
     4.3.  Sending an Relayed Echo Reply  . . . . . . . . . . . . . .  9
     4.4.  Receiving an Relayed Echo Reply  . . . . . . . . . . . . .  9
     4.5.  Sending an Echo Reply  . . . . . . . . . . . . . . . . . . 10
     4.6.  Receiving an Echo Reply  . . . . . . . . . . . . . . . . . 10
   5.  LSP Ping Relayed Echo Reply Example  . . . . . . . . . . . . . 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   7.  Backward Compatibility . . . . . . . . . . . . . . . . . . . . 12
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
     8.1.  New Message Type . . . . . . . . . . . . . . . . . . . . . 13
     8.2.  New TLV  . . . . . . . . . . . . . . . . . . . . . . . . . 13
     8.3.  New Return Code  . . . . . . . . . . . . . . . . . . . . . 13
   9.  Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . . 13
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
     10.2. Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14













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1.  Introduction

   This document describes extensions to the LSP Ping and Traceroute as
   specified in [RFC4379] that add as a Relayed Echo Reply mechanism
   that can be used to detect data plane failures in inter-AS and inter-
   area MPLS LSPs.  Prior to this extension, inter-AS functionality of
   [RFC4379] would fail in most deployment scenarios.  A new message
   referred to as "Relayed Echo Reply message" and a new TLV referred to
   as "Relay Node Address Stack TLV" are defined in this draft to
   overcome these deficiencies.

1.1.  Conventions Used in This Document

   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].


2.  Motivation

   LSP Ping [RFC4379] defines a mechanism to detect data plane failures
   and localize faults.  In the traceroute mode of LSP Ping procedure,
   the Echo Request message is send along the data plane between the
   originating LSR and one of the LSRs along the LSP, but is directed to
   be punted to the the control plane of each transit LSR.  The control
   plane of the receiving LSR then responds directly to the originator
   using an Echo Reply massage with proper information are required to
   send to the initiator at each transit LSR.  Each hop along the LSP is
   progressively probed by increasing the TTL of the Echo Request
   Message until the terminus of the LSP is reached.  Using this
   mechanism, the LSP data plane is tested, and any resulting faults can
   be localized.  Furthermore, this mechanism allows a network operator
   to create an accurate view of deployed LSP topology.

   The original mechanism specifies that The Echo Reply be sent back to
   the initiator usig a UDP packet containing directed back to the IPv4/
   IPv6 address of the originating LSR.  This works in adminitrative
   domains allowing IP address reachability and routing back to the
   originating LSR.  However, in practice, this is often not the case
   due to intra-provider routing policy, route hiding, network address
   translation at boundary autonomous system border routers (i.e.:
   ASBR), etc...  In fact, it is almost uniformly the case that in
   inter-AS scenarios to not allow the distribution or direct routing to
   the IP addresses of any of the nodes other than the ASBR.

   Figure 1 demonstrates how initiating a traceroute procedure on an
   ingress LSR (i.e.: PE1) of an LSP from PE1 to PE2, can be constructed
   between P nodes within an AS, which are then connected to ASBRs



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   interconnect both ASs.  In this case, if private addresses were in
   use within AS2, a traceroute from PE1 directed to PE2 could fail if
   the fault exists somewhere between AS2 and PE2 because P2 cannot
   forward packets back to PE1 given that it is a private address within
   AS1.  In this case, PE1 would detect a path break, as the Echo
   Request messages would not be responded to; however, localization of
   the actual fault would not be possible.



   +-------+   +-------+   +------+   +------+   +------+   +------+
   |       |   |       |   |      |   |      |   |      |   |      |
   |  PE1  +---+   P1  +---+ ASBR1+---+ ASBR2+---+  P2  +---+  PE2 |
   |       |   |       |   |      |   |      |   |      |   |      |
   +-------+   +-------+   +------+   +------+   +------+   +------+
   <---------------AS1-------------><---------------AS2------------>
   <---------------------------- LSP ------------------------------>


                Figure 1: Simple Inter-AS LSP Configuration


   A second example that illustrates how [RFC4379] would be insufficient
   would be the inter-area situation in a Seamless MPLS architecture
   [ietf-mpls-seamless] as shown below in Figure 2.  In the example P
   nodes the in core network would not have IP reachable route to any of
   the ANs.  When tracing an LSP from AN to remote AN, the LSR1/LSR2
   node could not make a response to the Echo Request either, like P2
   node in the inter-AS scenario.


              +-------+   +-------+   +------+   +------+
              |       |   |       |   |      |   |      |
           +--+ AGN11 +---+ AGN21 +---+ ABR1 +---+ LSR1 +--> to AGN
          /   |       |  /|       |   |      |   |      |
   +----+/    +-------+\/ +-------+   +------+  /+------+
   | AN |              /\                     \/
   +----+\    +-------+  \+-------+   +------+/\ +------+
          \   |       |   |       |   |      |  \|      |
           +--+ AGN12 +---+ AGN22 +---+ ABR2 +---+ LSR2 +--> to AGN
              |       |   |       |   |      |   |      |
              +-------+   +-------+   +------+   +------+
   static route     ISIS L1 LDP             ISIS L2 LDP
   <-Access-><--Aggregation Domain--><---------Core--------->


                   Figure 2: Seamless MPLS Architecture




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   This remainder of this document describes extensions to the LSP Ping
   mechanism to facillitate a response from the replying LSR using a
   simple mechanism that uses the ASBRs to relay the message back to the
   initiator.  This approach will work because every subsequent AS can
   and must have a route back to a connected AS.  Using a recursive
   approach, intermediate ASs can relay the message toward each other
   until the final AS is reached.  At this point, the ASBR must have a
   route to the initiating LSR because it is directly attached to it.
   This is achieved by augmenting the replying LSR's LSP Ping algorithm
   to send a response to a relay node (as indicated by the Relay Node
   Address Stack TLV), and the response would be relayed to the next
   relay node (i.e.: ASBR), until it reaches the ultimate ASBR.  At that
   point the ASBR should be able to resolve a local route to the
   initiator.


3.  Extensions

   RFC4379 describes the basic MPLS LSP Ping mechanism, which defines
   two message types.  This draft defines a new message, Relayed Echo
   Reply message.  This new message is used to replace Echo Reply
   message which is sent from the replying LSR to a relay node or from a
   relay node to another relay node.

   A new TLV named Relay Node Address Stack TLV is defined in this
   draft, to carry the IP addresses of the possible relay nodes for the
   replying LSR.

   In addition, a new Return Code is defined to notify the initiator
   that the packet length was exceeded by the Relay Node Address Stack
   TLV unexpected.

   It should be noted that this document focuses only on detecting the
   LSP which is setup using a uniform type of IP address.  That is, all
   hops between the originator and terminus use one address type of
   address) to address their control planes.  This does not preclude
   nodes that support both IPv6 and IPv4 addresses simultaneously, but
   the entire path MUST be addressible using only one address family
   type.  Support for mixed IPv4-only and IPv6-only is beyond the scope
   of this document.

3.1.  Relayed Echo Reply message

   The Relayed Echo Reply message is a UDP packet, and the UDP payload
   has the same format with Echo Request/Reply message.  A new message
   type is requested from IANA.





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   New Message Type:
       Value    Meaning
       -----    -------
       TBD      MPLS Relayed Echo Reply


   The TCP and UDP port number 3503 has been allocated in [RFC4379] by
   IANA for LSP Ping messages.  The Relayed Echo Reply message will use
   the same port number.

3.2.  Relay Node Address Stack

   The Relay Node Address Stack TLV is an optional TLV.  It MUST be
   carried in the Echo Request, Echo Reply and Relayed Echo Reply
   messages if the echo reply relayed mechanism described in this draft
   is required.  Figure 3 illustrates the TLV format.

     0                   1                     2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                Type           |               Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Initiator Source Port       |   Number of Relayed Addresses |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     ~                Stack of Relayed Addresses                     ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                  Figure 3: Relay Node Address Stack TLV

   -  Type: to be assigned by IANA.  A suggested value is assigned from
      32768-49161 as suggested by RFC4379 Section 3.

   -  Length: The Length of the Value field in octets.

   -  Initiator Source Port: The port that the initiator sends the Echo
      Request message, and also the port that expected to receive the
      Echo Reply message.

   -  Number of Relayed Addresses: An integer indicating the number of
      relayed addresses in the stack.








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   -  Stack of Relayed Addresses: A list of relay node addresses.

   The format of each relay node address is as below:

     0                   1                     2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Address  Type          | Address Length|  Reserved   |K|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~           Relayed Address (0, 4, or 16 octects)               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type#   Address Type   Address Length
   ----    ------------   ------------
   0       Unspecified    0
   1       IPv4           4
   2       IPv6           16

   Reserved: This field is reserved for future use and MUST be set to
   zero.

   K bit:

   If the K bit is set to 1, then this sub-TLV SHOULD be kept in Relay
   Node Address Stack, SHOULD not be deleted in compress process of
   section 4.2.  The K bit may be set by ASBRs which address would be
   kept in the stack if necessary.

   If the K bit is set to 0, then this sub-TLV SHOULD be processed
   normally according to section 4.2.

   Relayed Address: This field specifies the node address, either IPv4
   or IPv6.

3.3.  New Return Code

   A new Return Code is used by the replying LSR to notify the initiator
   that the packet length was exceeded by the Relay Node Address Stack
   TLV unexpected.

   New Return Code:
       Value    Meaning
       -----    -------
       TBD      Response Packet length was exceeded by the Relay Node
                Address Stack TLV unexpected





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4.  Procedures

4.1.  Sending an Echo Request

   In addition to the procedures described in Section 4.3 of [RFC4379],
   a Relay Node Address Stack TLV MUST be carried in the Echo Request
   message for facillitate the relay functionality.

   When the Echo Request is first sent by initiator supporting these
   extensions, a Relay Node Address Stack TLV with the initiator address
   in the stack and its source port MUST be included.

   For the subsequent Echo Request messages, the initiator would copy
   the Relay Node Address Stack TLV from the received Echo Reply
   message.

4.2.  Receiving an Echo Request

   In addition to the processes in Section 4.4 of [RFC4379], the
   procedures of the Relay Node Address Stack TLV are defined here.

   Upon receiving a Relay Node Address Stack TLV of the Echo Request
   message, the receiver would check the addresses of the stack in
   sequence from top to bottom, i.e., the first address in the stack
   would be first one to be checked, to find out the first public
   routable IP address.  Those address entries behind of the first
   routable IP address in the address list with K bit set to 0 would be
   deleted, and the address entry of the replying LSR would be added at
   the bottom of the stack.  Those address entries with K bit set to 1
   would be kept in the stack.  The updated Relay Node Address Stack TLV
   would be carried in the response message.

   If the replying LSR wishes to hide its routable address information,
   the address entry added in the stack would be a blank entry with
   Address Type set to Unspecified.  The blank address entry in the
   receiving Echo Request would be treated as an unroutable address
   entry.

   If the packet length was exceeded by the Relay Node Address Stack TLV
   unexpectedly, the TLV SHOULD be returned back unchanged in the echo
   response message.  And the new return code would help to notify the
   initiator of the situation.

   If the first routable IP address is the first address in the stack,
   the replying LSR would respond an Echo Reply message to the
   initiator.

   If the first routable IP address is of an intermediate node, other



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   than the first address in the stack, the replying LSR would send an
   Relayed Echo Reply instead of an Echo Reply in response.

   An LSR not recognize the Relay Node Address Stack TLV, SHOULD ignore
   it according to section 3 of RFC4379.

4.3.  Sending an Relayed Echo Reply

   The Relayed Echo Reply is sent in two cases:

   1.  When the replying LSR received an Echo Request with the initiator
   IP address in the Relay Node Address Stack TLV is IP unroutable, the
   replying LSR would send an Relayed Echo Reply message to the first
   routable intermediate node.  The processing of Relayed Echo Reply is
   the same with the procedure of the Echo Reply described in Section
   4.5 of RFC4379, except the destination IP address and the destination
   UDP port of the message part.  The destination IP address of the
   Relayed Echo Reply is set to the first routable IP address from the
   Relay Node Address Stack TLV, and the destination UDP port is set to
   3503.

   2.  When the intermediate relay node received an Relayed Echo Reply
   with the initiator IP address in the Relay Node Address Stack TLV is
   IP unroutable, the intermediate relay node would send the Relayed
   Echo Reply to the next relay node with the content of the UDP packet
   unchanged.  The destination IP address of the Relayed Echo Reply is
   set to the first routable IP address from the Relay Node Address
   Stack TLV.  Both the source and destination UDP port should be 3503.

4.4.  Receiving an Relayed Echo Reply

   Upon receiving an Relayed Echo Reply message with its address as the
   destination address in the IP header, the relay node should check the
   address items in Relay Node Address Stack TLV in sequence and find
   the first routable node address.

   If the first routable address is the top one of the address list,
   i.e., the initiator address, the relay node should send an Echo Reply
   message to the initiator containing the same payload with the Relayed
   Echo Reply message received.

   If the first routable address is not the top one of the address list,
   i.e., another intermediate relay node, the relay node should send an
   Relayed Echo Reply message to this relay node with the payload
   unchanged.






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4.5.  Sending an Echo Reply

   The Echo Reply is sent in two cases:

   1.  When the replying LSR received an Echo Request with the initiator
   IP address in the Relay Node Address Stack TLV is IP routable, the
   replying LSR would send an Echo Reply to the initiator.  In addition
   to the procedure of the Echo Reply described in Section 4.5 of
   RFC4379, the Relay Node Address Stack TLV would be carried in the
   Echo Reply.

   2.  When the intermediate relay node LSR received an Relayed Echo
   Reply with the initiator IP address in the Relay Node Address Stack
   TLV is IP routable, the intermediate relay node would send the Echo
   Reply to the initiator with the payload no changes other than the
   Message Type field.  The destination IP address of the Echo Reply is
   set to the initiator IP address, and the destination UDP port would
   be copied from the Initiator Source Port field of the Relay Node
   Address Stack TLV.  The source UDP port should be 3503.

4.6.  Receiving an Echo Reply

   In addition to the processes in Section 4.6 of RFC4379, the initiator
   would copy the Relay Node Address Stack TLV received in the Echo
   Reply to the next Echo Request.


5.  LSP Ping Relayed Echo Reply Example

   Considering the inter-AS scenario in Figure 4 below.



   +-------+   +-------+   +------+   +------+   +------+   +------+
   |       |   |       |   |      |   |      |   |      |   |      |
   |  PE1  +---+   P1  +---+ ASBR1+---+ ASBR2+---+  P2  +---+  PE2 |
   |       |   |       |   |      |   |      |   |      |   |      |
   +-------+   +-------+   +------+   +------+   +------+   +------+
   <---------------AS1-------------><---------------AS2------------>
   <--------------------------- LSP ------------------------------->


                      Figure 4: Example Inter-AS LSP


   In the example, an LSP has been created between PE1 to PE2.  When
   performing LSP traceroute on the LSP the first Echo Request sent by
   PE1 with outter-most label TTL=1, contains the Relay Node Address



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   Stack TLV with the only address of PE1.

   After processed by P1, P1's address will be added in the Relay Node
   Address Stack TLV address list following PE1's address in the Echo
   Reply.

   PE1 copies the Relay Node Address Stack TLV into the next Echo
   Request when receiving the Echo Reply.

   Upon receiving the Echo Request, ASBR1 checks the address list in the
   Relay Node Address Stack TLV in sequence, and finds out that PE1
   address is routable.  Then deletes P1 address, and adds its own
   address following PE1 address.  As a result, there would be PE1
   address followed by ASBR1 address in the Relay Node Address Stack TLV
   of the Echo Reply sent by ASBR1.

   PE1 then sends an Echo Request with outter-most label TTL=3,
   containing the Relay Node Address Stack TLV copied from the received
   Echo Reply message.  Upon receiving the Echo Request message, ASBR2
   checks the address list in the Relay Node Address Stack TLV in
   sequence, and finds out that PE1 address is IP route unreachable, and
   ASBR1 address is the first routable one in the Relay Node Address
   Stack TLV.  ASBR2 adds its address as the last address item following
   ASBR1 address in Relay Node Address Stack TLV, sets ASBR1 address as
   the destination address of the Relayed Echo Reply, and sends the
   Relayed Echo Reply to ASBR1.

   Upon receiving the Relayed Echo Reply from ASBR2, ASBR1 checks the
   address list in the Relay Node Address Stack TLV in sequence, and
   finds out that PE1 address is first routable one in the address list.
   Then ASBR1 send an Echo Reply to PE1 with the payload of received
   Relayed Echo Reply no changes other than the Message Type field.

   For the Echo Request with outter-most label TTL=4, P2 checks the
   address list in the Relay Node Address Stack TLV in sequence, and
   finds out that both PE1 and ASBR1 addresses are not IP routable, and
   ASBR2 address is the first routable address.  And P2 would send an
   Relayed Echo Reply to ASBR2 with the Relay Node Address Stack TLV of
   four addresses, PE1, ASBR1, ASBR2 and P2 address in sequence.

   Then according to the process described in section 4.4, ASBR2 would
   send the Relayed Echo Reply to ASBR1.  Upon receiving the Relayed
   Echo Reply, ASBR1 would send an Echo Reply to PE1 as PE1 address is
   routable.  And as relayed by ASBR2 and ASBR1, the echo response would
   finally be sent to the initiator PE1.

   For the Echo Request with outter-most label TTL=5, the echo response
   would relayed to PE1 by ASBR2 and ASBR1, similar to the case of



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   TTL=4.

   The Echo Reply from the replying node which has no reachable route to
   the initiator is finally transmitted to the initiator by multiple
   relay nodes.


6.  Security Considerations

   The Relayed Echo Reply mechanism for LSP Ping creates an increased
   risk of DoS by putting the IP address of a target router in the Relay
   Node Address Stack.  These messages then could be used to attack the
   control plane of an LSR by overwhelming it with these packets.  A
   rate limiter SHOULD be applied to the well-known UDP port on the
   relay node as suggested in RFC4379.  The node which acts as a relay
   node SHOULD validate the relay reply against a set of valid source
   addresses and discard packets from untrusted border router addresses.
   An implementation SHOULD provide such filtering capabilities.

   If an operator wants to obscure their nodes, it is RECOMMENDED that
   they they may replace the failed node that originated the Echo Reply
   with their own address.

   Other security considerations discussed in [RFC4379], are also
   applicable to this document.


7.  Backward Compatibility

   When one of the nodes along the LSP does not support the mechanism
   specified in this draft, the node will ignore the Relay Node Address
   Stack TLV as described in section 4.2.  Then the initiator may not
   receive the Relay Node Address Stack TLV in Echo Reply message from
   that node.  In this case, an indication should be reported to the
   operator, and the Relay Node Address Stack TLV in the next Echo
   Request message should be copied from the previous Echo Request, and
   continue the ping process.  If the node described above is located
   between the initiator and the first relay node, the ping process
   could continue without interruption.


8.  IANA Considerations

   IANA is requested to assign one new Message Type, one new TLV and one
   new Return Code.






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8.1.  New Message Type

   New Message Type:
        Value    Meaning
        -----    -------
        TBD      MPLS Relayed Echo Reply

8.2.  New TLV

   New TLV: Routable Relay Node Address TLV
        Type    Meaning
        ----    --------
        TBD     Relay Node Address Stack TLV

   A suggested value is assigned from 32768-49161 as suggested by
   RFC4379 Section 3.

8.3.  New Return Code

   New Return Code:
       Value    Meaning
       -----    -------
       TBD      Response Packet length was exceeded by the Relay Node
                Address Stack TLV unexpected



9.  Acknowledgement

   The authors would like to thank Carlos Pignataro, Xinwen Jiao, Manuel
   Paul, Loa Andersson, Wim Henderickx, Mach Chen and Thomas Morin for
   their valuable comments and suggestions.


10.  References

10.1.  Normative References

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

   [RFC4377]  Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S.
              Matsushima, "Operations and Management (OAM) Requirements
              for Multi-Protocol Label Switched (MPLS) Networks",
              RFC 4377, February 2006.

   [RFC4378]  Allan, D. and T. Nadeau, "A Framework for Multi-Protocol
              Label Switching (MPLS) Operations and Management (OAM)",



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              RFC 4378, February 2006.

   [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.

10.2.  Informative References

   [ietf-mpls-seamless]
              Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
              M. and D. Steinberg, "Seamless MPLS Architecture",
              draft-ietf-mpls-seamless-mpls-02 , October 2012.


Authors' Addresses

   Ryan Zheng (editor)
   ZTE
   50, Ruanjian Avenue
   Nanjing, 210012, China

   Email: zheng.zhi@zte.com.cn


   Lizhong Jin (editor)
   ZTE
   889, Bibo Road
   Shanghai, 201203, China

   Email: lizho.jin@gmail.com


   Thomas Nadeau (editor)
   Juniper Networks
   Westford, MA

   Email: tnadeau@juniper.net





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   George Swallow (editor)
   Cisco
   300 Beaver Brook Road
   Boxborough , MASSACHUSETTS 01719, USA

   Email: swallow@cisco.com













































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