MPLS Working Group                                             R.Bonica
Internet Draft                                              MCIWorldCom
Document: draft-ietf-mpls-icmp-02.txt                          D.Tappan
                                                          Cisco Systems
                                                                  D.Gan                                             R. Bonica
Internet-Draft                                                    D. Gan
Expires: February 3, 2006                               Juniper Networks
                                                               D. Tappan
                                                     Cisco Systems, Inc.
                                                          August 2000 2, 2005

           ICMP Extensions for MultiProtocol Label Switching

Status of this Memo

   This document

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1. Abstract

   This Internet-Draft will expire on February 3, 2006.

Copyright Notice

   Copyright (C) The current Internet Society (2005).


   This memo proposes extensions to ICMP that permit Label Switching
   Routers to append MPLS information to ICMP messages.

Table of Contents

   1.  Conventions Used In This Document  . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Application to TRACEROUTE  . . . . . . . . . . . . . . . . . .  5
   4.  Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     5.1   Common Header  . . . . . . . . . . . . . . . . . . . . . .  8
     5.2   Object Header  . . . . . . . . . . . . . . . . . . . . . .  8
     5.3   MPLS Stack Entry Object Class  . . . . . . . . . . . . . .  9
     5.4   Extended Payload Object Class  . . . . . . . . . . . . . . 10
   6.  Backward Compatibility . . . . . . . . . . . . . . . . . . . . 11
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   9.  Normative References . . . . . . . . . . . . . . . . . . . . . 13
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13
       Intellectual Property and Copyright Statements . . . . . . . . 15

1.   Conventions used in this document Used In This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC-2119].

3. RFC2119 [1].

2.  Introduction

   Routers and destination hosts

   IP routers use the Internet Control Message Protocol (ICMP) [RFC-792] [2] to
   convey control information to source hosts.  Network operators use
   this information to diagnose routing problems.

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   When a router receives an undeliverable IP datagram, it can send an
   ICMP message to the host that originated the datagram.  The ICMP
   message indicates why the datagram could not be delivered.  It also
   contains the IP header and leading payload octets of the "original

   In this document, the term "original datagram" refers to the datagram
   to which the ICMP message is a response.

   MPLS Label Switching Routers (LSR) also use ICMP to convey control
   information to source hosts.  Sections 2.3 and 2.4 of [ENCODE] RFC 3032 [3]
   describe the interaction between MPLS and ICMP.

   When an LSR receives an undeliverable MPLS encapsulated datagram, it
   removes the entire MPLS label stack, exposing the previously
   encapsulated IP datagram.  The LSR then submits the IP datagram to a
   network-forwarding module for an
   error processing. processing module.  Error processing can include ICMP message

   The ICMP message indicates why the original datagram could not be
   delivered.  It also contains the IP header and leading octets of the
   original datagram.

   The ICMP message, however, includes contains no information regarding the MPLS
   label stack that encapsulated the original datagram when it arrived
   at the LSR.  This omission is significant because the LSR would have
   routed the original datagram based upon information contained by the
   MPLS label stack.

   The current

   This memo proposes extensions to ICMP that permit an LSR to append
   MPLS label stack information to ICMP messages.  ICMP messages
   regarding MPLS encapsulated datagrams SHOULD include the MPLS label
   stack, as it arrived at the router that is sending the ICMP message.
   The ICMP message MUST also include the IP header and leading payload
   octets of the original datagram.

   Network operators will use this information

3.  Application to diagnose routing

4. Motivation TRACEROUTE

   ICMP extensions defined in the current this memo support enhancements to
   TRACEROUTE.  The enhanced TRACEROUTE, like older implementations,
   indicates which nodes the original datagram visited en route to its
   destination.  It differs from older implementations in that it also
   indicates the original datagrams MPLS encapsulation status as it
   arrived at each node.

   Figure 1 contains sample output from an enhanced TRACEROUTE

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     > traceroute

     traceroute to, (, 30 hops max, 40 byte packets

      1 1.281 (  0.661 ms 1.103  0.618 ms 1.096  0.579 ms

      2 1.281 (  0.861 ms 1.103  0.718 ms 1.096  0.679 ms mplsLabel1=2001

        MPLS Label=100048 Exp=0 TTL=1 S=1

      3 1.281 (  0.822 ms 1.103  0.731 ms 1.096  0.708 ms mplsLabel1=2002

        MPLS Label=100016 Exp=0 TTL=1 S=1

      4 1.281 ms 1.103 ms 1.096 ms mplsLabel1=2003
        5 1.281 ms 1.103 (  0.961 ms 1.096  8.676 ms
        6 1.281 ms 1.103 ms 1.096  0.875 ms

                Figure 1. 1: Enhanced TRACEROUTE sample output

5. Sample Output

4.  Disclaimer

   The current

   This memo does not define the general relationship between ICMP and
   MPLS.  Sections 2.3 and 2.4 of [ENCODE] RFC3032 define this relationship.

   Specifically, this document defers to [ENCODE] RFC3032 with respect to the
   following issues:

      - conditions upon which an LSR emits ICMP messages

      - handling of ICMP messages bound for hosts that are identified by
      private addresses

   The current memo does not define encapsulation specific TTL
   manipulation procedures.  It defers to Section 10 5.4 of [MPLSATM] RFC 3034 [4]
   and Section 5.4 10 of [MPLSFRAME] RFC 3035 [5] in this matter.

   When encapsulation specific TTL manipulation procedures defeat the
   basic TRACEROUTE mechanism, they will also defeat enhanced TRACEROUTE

   The current memo does not address extensions to ICMPv6.  These should
   be addressed in a separate draft.

6. Formal

5.  Syntax

   This section defines a data structure that an LSR can append to
   selected ICMP messages.  The data structure contains the MPLS label
   stack that encapsulated the original datagram when it arrived at the


   In theory, the data structure defined herein can be appended to the
   following ICMP message types:

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      Destination Unreachable

      Time Exceeded

      Parameter Problem

      Source Quench


   However, in practice, it would only be useful when appended to the
   Destination Unreachable and Time Exceeded messages.

   According to RFC-792, bytes 0 through 19 of any ICMP message contain
   a header whose format is analogous to that of the IP datagram.  Bytes
   20 through 23 contain an ICMP message type, code and checksum.  Bytes
   24 through 27 contain message specific data.

   Also according to RFC-792, the final field contained by each of the
   ICMP message types listed above begins at byte 28.  It reflects the
   IP header and leading 64 bits of the original datagram. [RFC-1812]  RFC 1812 [6]
   recommends that this final field be extended to include as much of
   the original datagram as possible.

   When an LSR appends the data structure defined herein to an ICMP
   message, the final field of the ICMP message body MUST contain the
   first 128 octets of the original datagram.  At least 20 of these 128
   octets represent the IP header of the original datagram.

   If the original datagram was shorter than 128 octets, the final field
   MUST be padded with 0's.

   When an LSR appends the data structure defined herein to an ICMP
   message, the ICMP "total length" MUST be equal adjusted appropriately to
   include the data structure
   length plus 156. The first octet of the data structure must be
   displaced 156 octets from the beginning of the ICMP message. structure.

   The data structure defined in this section consists of a common
   header followed by object instances.  Each object instance consists
   of an object header plus contents.

   Currently, two object classes are defined.  One object class contains
   an entire MPLS label stack, formatted exactly as it was when it
   arrived at the LSR that sends the ICMP message.  The other contains
   some portion of the original datagram that could not be included in
   the final field of the ICMP message body (i.e., the octet 129 and

   Both object classes are optional.

   In the future, additional object classes may be defined.

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5.1  Common Header

             0             1            2              3
      | Vers |     (Reserved)     |          Checksum         |

                          Figure 2: Common Header

   The fields in the common header are as follows:

   Vers: 4 bits

      ICMP extension version number.  This is version 2.

   Checksum: 16 bits

      The one's complement of the one's complement sum of the data
      structure, with the checksum field replaced by zero for the
      purpose of computing the checksum.  An all-zero value means that
      no checksum was transmitted.

      If the checksum field contains a value other than described above,
      the ICMP message does not include the extensions described in this
      memo.  This, however, does not imply that the ICMP message is
      malformed.  It may be in strict compliance with RFC-1812.

   Reserved: Must be set to 0.


5.2  Object Header

   Every object consists of one or more 32-bit words with a one-word
   header, with the
   header.  The following format: is the format of the one-word header:

      |           Length          | Class-Num   | C-Type      |
      |                                                       |
      |               // (Object contents) //                 |
      |                                                       |

                          Figure 3: Object Header

   An object header has the following fields:

   Length: 16 bits

      Length of the object, measured in octets, including the object
      header and object contents.
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   Class-Num: 8 bits

      Identifies object class.

   C-Type: 8 bits

      Identifies object sub-type.


5.3  MPLS Stack Entry Object Class

   A single instance of the MPLS Entry Object class represents the
   entire MPLS label stack, formatted exactly as it was when it arrived
   at the LSR that sends the ICMP message

   In the illustration below, octets 0-3 depict the first member of the
   MPLS label stack.  Each remaining member of the MPLS label stack is
   represented by another 4 octets that share the same format.

   Syntax follows:

   MPLS Stack Entry Class = 1, C-Type = 1.

              0             1             2            3
      |              Label               |EXP |S|     TTL     |
      |                                                       |
      |       // Remaining MPLS Stack Entries //              |
      |                                                       |

                  Figure 4: MPLS Stack Entry Object Class

   Label: 20 bits

   Exp: Experimental Use, 3 bits

   S: Bottom of Stack, 1 bit

   TTL: Time to Live, 8 bits


5.4  Extended Payload Object Class

   An instance of the Extended Payload Object class represents some
   portion of the original datagram that could not be fit in the final
   field of the ICMP message body (i.e., octets beyond 128).

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   Syntax follows:

   MPLS Stack Entry Class = 2, C-Type = 1.

              0             1             2            3
      |                                                       |
      |       // Additional bytes of original datagram //     |
      |                                                       |


                  Figure 5: Extended Payload Object Class

6.  Backward Compatibility

   ICMP extensions proposed in this document MUST be backward compatible
   with the syntax described in RFC-792.  Extensions proposed in this
   memo MUST NOT change or deprecate any field defined in RFC-
   792. RFC-792.

   The extensions defined herein are in keeping with the spirit, if not
   the letter of RFC-1812.  In order to support IP-in-IP tunneling, RFC-
   1812 extends the final field of selected ICMP messages to include a
   greater portion of the original datagram.  Unfortunately, it extends
   this field to a variable length without adding a length attribute.

   This memo binds the length of that final field to an arbitrarily
   large value (128 octets).  Fixing the length of that field
   facilitates extension of the ICMP message.  An additional object is
   provided through which octets 129 and beyond can be appended to the
   ICMP message.

   As few datagrams contain L3 or L4 header information beyond octet
   128, it is unlikely that the extensions described herein will disable
   any applications that rely upon RFC-1812 style ICMP messages.


7.  Security Considerations

   This memo presents no security considerations beyond those already
   presented by current ICMP applications (e.g., traceroute).

9. References

   [ARCH], Rosen, E., Viswanathan, A.,

8.  IANA Considerations

   IANA should establish a registry of ICMP extention classes and R. Callon, "Multiprotocol
   Label Switching Architecture", Internet Draft <draft-ietf-mpls-arch-
   06.txt>, August, 1999

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   [ENCODE], class-

9.  Normative References

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

   [2]  Postel, J., "Internet Control Message Protocol", STD 5, RFC 792,
        September 1981.

   [3]  Rosen, E., Rekhter, Y., Tappan, D, Farinacci, D., Fedorkow, G., Rekhter, Y., Farinacci, D.,
        Li, T., and A. Conta, A., "MPLS Label Stack Encoding", Internet
   Draft, <draft-ietf-mpls-label-encapse-07.txt>, September 1999.

   [MPLSATM], RFC 3032,
        January 2001.

   [4]  Conta, A., Doolan, P., and A. Malis, "Use of Label Switching on
        Frame Relay Networks Specification", RFC 3034, January 2001.

   [5]  Davie, B., Lawrence, J., McCloghrie, K., Rekhter, Y., Rosen, E., Swallow, G, G.,
        Rekhter, Y., and P. Doolan, "MPLS using LDP and ATM VC
   <draft-ietf- mpls-atm-04.txt>, June 2000.

   [MPLSFRAME], Conta, A., Doolan, P., Malis, A., "Use of Label
   Switching on Frame Relay Networks", <draft-ietf-mpls-fr-06.txt>,
   June, 2000.

   [RFC-792], Postel, J., "Internet Control Message Protocol", RFC 792,
   ISI, September 1981.

   [RFC-1812], 3035, January 2001.

   [6]  Baker, F., "Requirements for IP Version 4 Routers", RFC 1812,
        June 1995.

   [RFC-2026], Bradner, S., "Internet Standards Process Revision 3",
   RFC 2026, Harvard University, October 1996.

   [RFC-2119], Bradner, S,, "Key words for use in RFCs to Indicate
   Requirement Levels", RFC 2119, Harvard University, March 1997

10.  Acknowledgments

   Thanks to Yakov Rekhter and Mike Heard for their contributions to
   this memo.

11. Author's

Authors' Addresses

   Ronald P. Bonica
   MCI WorldCom
   22001 Loudoun County Pkwy
   Ashburn, Virginia, 20147
   Phone: 703 886 1681
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, VA  20171


   Der-Hwa Gan
   Juniper Networks
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089

   Daniel C. Tappan
   Cisco Systems Systems, Inc.
   250 Apollo Drive
   Chelmsford, Massachusetts, MA  01824


   Der-Hwa Gan
   Juniper Networks
   385 Ravendale Drive
   Mountain View, California 94043
 Bonica,Tappan,Gan   Draft-Expires February 2001                     8

 Bonica,Tappan,Gan   Draft-Expires February 2001                     9

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