Skip to main content

ICMP Extensions for Multiprotocol Label Switching

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 4950.
Authors Ron Bonica , Der-Hwa Gan , Carlos Pignataro , Dan Tappan
Last updated 2015-10-14 (Latest revision 2007-02-01)
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
Stream WG state WG Document
Document shepherd (None)
IESG IESG state Became RFC 4950 (Proposed Standard)
Action Holders
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD Ross Callon
Send notices to (None)
MPLS Working Group                                             R. Bonica
Internet-Draft                                                    D. Gan
Intended status: Standards Track                        Juniper Networks
Expires: August 4, 2007                                        D. Tappan
                                                            C. Pignataro
                                                     Cisco Systems, Inc.
                                                        January 31, 2007

           ICMP Extensions for MultiProtocol Label Switching

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   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."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on August 4, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).


   This memo defines an extension object that can be appended to
   selected multi-part ICMP messages.  This extension permits Label
   Switching Routers to append MPLS information to ICMP messages, and
   has already been widely deployed.

Bonica, et al.           Expires August 4, 2007                 [Page 1]
Internet-Draft                  ICMP MPLS                   January 2007

Table of Contents

   1.  Conventions Used In This Document . . . . . . . . . . . . . . . 3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Application to TRACEROUTE . . . . . . . . . . . . . . . . . . . 4
   4.  Disclaimer  . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  MPLS Label Stack Object . . . . . . . . . . . . . . . . . . . . 5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9

Bonica, et al.           Expires August 4, 2007                 [Page 2]
Internet-Draft                  ICMP MPLS                   January 2007

1.   Conventions Used In This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC2119 [RFC2119].

2.  Introduction

   IP routers use the Internet Control Message Protocol, ICMPv4
   [RFC0792] and ICMPv6 [RFC4443], to convey control information to
   source hosts.  Network operators use this information to diagnose
   routing problems.

   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
   datagram" to which the ICMP message is a response.

   MPLS Label Switching Routers (LSR) also use ICMP to convey control
   information to source hosts.  Section 2.3 of [RFC3032] describes the
   interaction between MPLS and ICMP, and Sections 2.4 and 3 of
   [RFC3032] provide applications of that interaction.

   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 an
   error 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, 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
   forwarded the original datagram based upon information contained by
   the MPLS label stack.

   This memo defines an ICMP extension object that permits an LSR to
   append MPLS information to ICMP messages.  Selected ICMP messages
   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.

   The ICMP extensions defined in this document must be preceded by an

Bonica, et al.           Expires August 4, 2007                 [Page 3]
Internet-Draft                  ICMP MPLS                   January 2007

   ICMP Extension Structure Header and an ICMP Object Header.  Both are
   defined in [I-D.bonica-internet-icmp].

   The ICMP extension defined in this document is equally applicable to
   ICMPv4 [RFC0792] and ICMPv6 [RFC4443].  Throughout this document,
   unless otherwise specified, the acronym ICMP refers to multi-part
   ICMP messages, encompassing both ICMPv4 and ICMPv6.

3.  Application to TRACEROUTE

   The ICMP extension defined in this memo supports enhancements to
   TRACEROUTE.  Enhanced TRACEROUTE applications, like older
   implementations, indicate which nodes the original datagram visited
   en route to its destination.  They differ from older implementations
   in that they also reflect the original datagram's MPLS encapsulation
   status as it arrived at each node.

   Figure 1 contains sample output from an enhanced TRACEROUTE

     > traceroute

     traceroute to (, 30 hops max, 40 byte packets

      1 (  0.661 ms  0.618 ms  0.579 ms

      2 (  0.861 ms  0.718 ms  0.679 ms

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

      3 (  0.822 ms  0.731 ms  0.708 ms

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

      4 (  0.961 ms  8.676 ms  0.875 ms

                Figure 1: Enhanced TRACEROUTE Sample Output

4.  Disclaimer

   This memo does not define the general relationship between ICMP and
   MPLS.  Section 2.3 of [RFC3032] defines this relationship.

Bonica, et al.           Expires August 4, 2007                 [Page 4]
Internet-Draft                  ICMP MPLS                   January 2007

   The current memo does not define encapsulation specific TTL
   manipulation procedures.  It defers to Section 5.4 of RFC 3034
   [RFC3034] and Section 10 of [RFC3035] in this matter.

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

5.  MPLS Label Stack Object

   The MPLS Label Stack Object can be appended to the ICMP Time Exceeded
   and Destination Unreachable messages.  A single instance of the MPLS
   Label Stack Object represents the entire MPLS label stack, formatted
   exactly as it was when it arrived at the LSR that sends the ICMP

   Figure 2 depicts the MPLS Label Stack Object.  It must be preceded by
   an ICMP Extension Structure Header and an ICMP Object Header.  Both
   are defined in [I-D.bonica-internet-icmp].

   In the object payload, 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.

                   Class-Num = 1, MPLS Label Stack Class
                   C-Type = 1, Incoming MPLS Label Stack
                   Length = 4 + 4 * (number of MPLS LSEs)

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

                     Figure 2: MPLS Label Stack Object

   Label: 20 bits

   Exp: Experimental Use, 3 bits

   S: Bottom of Stack, 1 bit

Bonica, et al.           Expires August 4, 2007                 [Page 5]
Internet-Draft                  ICMP MPLS                   January 2007

   TTL: Time to Live, 8 bits

6.  Security Considerations

   This memo does not specify the conditions that trigger the generation
   of ICMP Messages for Labeled IP Packets.  It does not define the
   interaction between MPLS and ICMP.  However, this document defines an
   extension that allows an MPLS router to append MPLS information to
   multi-part ICMP messages, and therefore can provide the user of the
   traceroute application with additional information.  Consequently, a
   network operator may wish to provide this information selectively
   based on some policy; for example, only include the MPLS extensions
   in ICMP messages destined to addresses within the network management
   blocks with administrative control over the router.  An
   implementation could determine whether to include the MPLS Label
   Stack extensions based upon the destination address of the ICMP
   message, or based on a global configuration option in the router.
   Alternatively, an implementation may determine whether to include
   these MPLS extensions when TTL expires based on the number of label
   stack entries (depth of the label stack) of the incoming packet.
   Finally, an operator can make use of the TTL treatment on MPLS Pipe
   Model LSPs defined in [RFC3443] for a TTL-transparent mode of
   operation, that would prevent ICMP Time Exceeded altogether when
   tunneled over the MPLS LSP.

7.  IANA Considerations

   IANA is requested to assign the following object Class-num in the
   ICMP Extension Object registry:

             Class-Num   Description
                     1   MPLS Label Stack Class

   IANA is also requested to establish a registry for the corresponding
   class sub-type (C-Type) space, as follows:

             MPLS Label Stack Class Sub-types:

                C-Type  Description
                     1  Incoming MPLS Label Stack
             0xF7-0xFF  Reserved for private use

   C-Type values are assignable on a first-come-first-serve (FCFS) basis

Bonica, et al.           Expires August 4, 2007                 [Page 6]
Internet-Draft                  ICMP MPLS                   January 2007

8.  References

8.1.  Normative References

              Bonica, R., "Extended ICMP to Support Multi-part
              Messages", draft-bonica-internet-icmp-16 (work in
              progress), January 2007.

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, September 1981.

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

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, January 2001.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

8.2.  Informative References

   [RFC3034]  Conta, A., Doolan, P., and A. Malis, "Use of Label
              Switching on Frame Relay Networks Specification",
              RFC 3034, January 2001.

   [RFC3035]  Davie, B., Lawrence, J., McCloghrie, K., Rosen, E.,
              Swallow, G., Rekhter, Y., and P. Doolan, "MPLS using LDP
              and ATM VC Switching", RFC 3035, January 2001.

   [RFC3443]  Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing
              in Multi-Protocol Label Switching (MPLS) Networks",
              RFC 3443, January 2003.

Bonica, et al.           Expires August 4, 2007                 [Page 7]
Internet-Draft                  ICMP MPLS                   January 2007

Authors' Addresses

   Ronald P. Bonica
   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, Inc.
   250 Apollo Drive
   Chelmsford, MA  01824


   Carlos Pignataro
   Cisco Systems, Inc.
   7025 Kit Creek Road
   Research Triangle Park, N.C.  27709


Bonica, et al.           Expires August 4, 2007                 [Page 8]
Internet-Draft                  ICMP MPLS                   January 2007

Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at


   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).

Bonica, et al.           Expires August 4, 2007                 [Page 9]