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Versions: 00 01 02 03 04 05 06 07 08 09 RFC 5837

Internet                                                        A. Atlas
Internet-Draft                                                JR. Rivers
Expires: June 12, 2006                                      Google, Inc.
                                                               R. Bonica
                                                        Juniper Networks
                                                        December 9, 2005


               ICMP Extensions for Unnumbered Interfaces
                     draft-atlas-icmp-unnumbered-00

Status of this Memo

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   This Internet-Draft will expire on June 12, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This memo defines extensions to ICMP that permit identification of
   unnumbered interfaces.  The interface the IP packet was received upon
   can be identified by appending an ifIndex and/or a string describing
   the interface.  These extensions are defined to facilitate
   troubleshooting in network with unnumbered interfaces and parallel
   links.



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Table of Contents

   1.  Conventions Used In This Document . . . . . . . . . . . . . . . 3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Application to TRACEROUTE . . . . . . . . . . . . . . . . . . . 4
   4.  Interface Object  . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Interface Description Object  . . . . . . . . . . . . . . . . . 4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8







































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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 [4].


2.  Introduction

   IP routers use the Internet Control Message Protocol (ICMP) [1] to
   convey control information to source hosts.  Network operators use
   this information to diagnose routing problems.

   When a router generates an ICMP message, the source IP address can be
   any address of the router.  In common implementations, the IP address
   selected is that of the incoming interface of the packet that
   triggered the ICMP message.  This allows easy identification of
   specific interface and is very useful for troubleshooting
   connectivity issues.

   When a network uses unnumbered interfaces and parallel links, it is
   not currently possible to identify the specific incoming interface of
   a packet based upon the responding ICMP message.  This memo defines
   two extensions to ICMP that permit an operator to identify the
   specific incoming interface traversed by a packet that triggered an
   ICMP message.

   These two extensions are motivated by the desire for similar
   information to that for numbered interfaces.  In the case of
   traceroute, the ICMP message contains the interfaces's IP address;
   then that IP address is commonly resolved via DNS to provide a
   meaningful name for the interface that is easier for humans.  One
   extension permits a router to include the interface's ifIndex; this
   can be used in combination with the source IP address for management
   tasks.  The second extension permits a router to include an interface
   description string.

   The inclusion of an interface description may also be useful for
   numbered interfaces that use a private IP address that DNS cannot
   resolve for supported users of traceroute and other ICMP message
   triggers.

   The ICMP message MUST include the IP header and leading payload
   octets of the original datagram.  As described in [2], an ICMP
   Extension Structure Header MUST follow the octets from the original
   datagram and come before any ICMP Extension Objects.





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3.  Application to TRACEROUTE

   ICMP extensions defined in this memo support enhancements to
   TRACEROUTE.  The enhanced TRACEROUTE application, like older
   implementations, indicates which nodes the original datagram visited
   en route to its destination.  It differs from older implementations
   in that it also reflects the incoming interface on which the original
   packet arrived, even when that interface is unnumbered.


4.  Interface Object

   This section defines an ICMP extention object that can be appended to
   the ICMP Time Exceeded and Destination Unreachable messages.  One or
   more Interface Objects can be appended to these messages.

   Figure 1 depicts the Interface Object.  It must be preceded by an
   ICMP Extension Structure Header and an ICMP Object Header.  Both are
   defined in [2].  The ifIndex included is that assigned to the
   interface by the router in as specified by the Interfaces Group MIB
   [3].


          Interface Class-Num = 2,
             C-Type = 1  (Incoming Interface)

             0             1             2            3
     +-------------+-------------+-------------+-------------+
     |                Interface ifIndex                      |
     +-------------+-------------+-------------+-------------+

   Figure 1: Interface Object


5.  Interface Description Object

   This section defines an ICMP extention object that can be appended to
   the ICMP Time Exceeded and Destination Unreachable messages.  One or
   more Interface Description Objects can be appended to these messages.

   Figure 2 depicts the Interface Description Object.  It must be
   preceded by an ICMP Extension Structure Header and an ICMP Object
   Header.  Both are defined in [2].








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        Interface Class-Num = 3,
          C-Type = 1  (Incoming Interface Description encoded in ASCII)

                  0             1             2            3
          +-------------+-------------+-------------+-------------+
          |              Interface Description                    |
          +-------------+-------------+-------------+-------------+

   Figure 2: Interface Description Object

   Interface Description: This field MUST have a length that is a
   multiple of 4 bytes; the string should be padded with zeroes as
   necessary.  The description can be either the same content as the
   MIB-II ifDescription field or some other human-meaningful description
   of the interface.


6.  Security Considerations

   These extensions can provide the user of traceroute with additional
   network information that is not currently available.  It may be
   desirable to provide this information to a particular network's
   operators and not to others.  If such policy controls are desirable,
   then an implementation could determine what extensions to include
   based upon the destination IP address of the ICMP message.  For
   instance, there could be an interface description that is appropriate
   for all potential recipients; a more detailed description and the
   ifIndex could be included as well if the destination IP address is a
   management address of the network that has administrative control of
   the router.


7.  IANA Considerations

   IANA should should reserve from the ICMP Extension Object registry: 2
   for the Interface Object and 3 for the Interface Description Object.
   IANA should reserve from the Interface Object's C-type the value 1
   for Incoming Interface.  IANA should reserve from the Interface
   Description Object's C-type the value 1 for Incoming Interface
   Description in ASCII.

8.  Normative References

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

   [2]  Bonica, R., "Extending the Internet Control Message Protocol
        (ICMP)", draft-bonica-internet-icmp-00 (work in progress),



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        September 2005.

   [3]  McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB
        using SMIv2", RFC 2233, November 1997.

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












































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Authors' Addresses

   Alia K. Atlas
   Google, Inc.
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   USA

   Email: akatlas@google.com


   J.R. Rivers
   Google, Inc.
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   USA

   Email: jrrivers@google.com


   Ronald P. Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, VA  20171
   US

   Email: rbonica@juniper.net
























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