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Internet                                                   A. Atlas, Ed.
Internet-Draft                                                        BT
Expires: January 29, 2009                                      R. Bonica
                                                        Juniper Networks
                                                              JR. Rivers
                                                           Nuova Systems
                                                                 N. Shen
                                                                 E. Chen
                                                           Cisco Systems
                                                           July 28, 2008


           Extending ICMP to Identify the Receiving Interface
                     draft-atlas-icmp-unnumbered-05

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
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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 29, 2009.

Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   This memo defines ICMP extensions, using ICMP multi-part messages,
   through which a router or host can explicitly identify the interface



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   upon which an undeliverable datagram anrrived.  The incoming
   interface can be identified by ifIndex, name, and/or address, as
   already used in MIBs and by OSPF.  The extensions defined herein are
   particularly useful when troubleshooting networks with unnumbered
   interfaces, parallel interfaces and/or asymmetric routing.


Table of Contents

   1.  Conventions Used In This Document  . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Applications . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Application to TRACEROUTE  . . . . . . . . . . . . . . . .  4
     3.2.  Policy and MTU Detection . . . . . . . . . . . . . . . . .  4
   4.  Interface Information Object . . . . . . . . . . . . . . . . .  5
     4.1.  C-type meaning in an Interface Information Object  . . . .  5
     4.2.  Interface Name Sub-Object  . . . . . . . . . . . . . . . .  7
     4.3.  Interface Information Object Description . . . . . . . . .  8
     4.4.  Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
   Intellectual Property and Copyright Statements . . . . . . . . . . 14
























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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 [RFC2119].


2.  Introduction

   IP devices use the Internet Control Message Protocol (ICMP) [RFC0792]
   (ICMPv6) [RFC4443] to convey control information.  In particular,
   when an IP device receives a datagram that it cannot forward, it may
   send an ICMP message to the datagram's originator.  Network operators
   and higher level protocols use these ICMP messages to detect and
   diagnose network issues.

   In the nominal case, the source address of the ICMP message
   identifies the interface upon which the non-forwardable datagram
   arrived.  However, in many cases, the incoming interface is not
   identified by the ICMP message at all.  Details follow:

   According to RFC1812 [RFC1812], when a router generates an ICMP
   message, the source address of that ICMP message MUST be one of the
   following:

   o  one of the IP addresses associated with the physical interface
      over which the ICMP message is transmitted
   o  if that interface has no IP addresses associated with it, the
      device's router-id or host-id is used instead.

   If the following conditions are true, the source address of the ICMP
   message identifies the interface upon which the non-forwardable
   datagram arrived:

   o  the device originates an ICMP message through the same interface
      upon which the non-forwardable datagram was received.
   o  that interface is numbered.

   However, the transmitting and incoming interfaces may be different
   due to an asymmetric return path, which can occur due to asymmetric
   link costs, parallel links or ECMP.

   For ICMPv6, the asymmetric issues need not be an issue, since there
   is more flexibility for ICMPv6, as defined in RFC4443 [RFC4443].  For
   responses to messages sent to addresses that aren't the router's, the
   source address must be chosen as follows:





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   o  the Source Address of the ICMPv6 packet MUST be a unicast address
      belonging to the node.  The address SHOULD be chosen according to
      the rules that would be used to select the source address for any
      other packet originated by the node, given the destination address
      of the packet.  However, it MAY be selected in an alternative way
      if this would lead to a more informative choice of address
      reachable from the destination of the ICMPv6 packet.

   For both ICMP and ICMPv6, when a network uses unnumbered interfaces,
   it is not possible to identify the incoming interface.  The
   extensions defined in this memo permit an ICMP originator to identify
   the interface through which the datagram that elicited the ICMP
   messages arrived.

   Using the extension defined herein, an IP device can explicitly
   identify the incoming interface by any or all of the following:

   o  IPv4 address
   o  IPv6 address
   o  name
   o  ifIndex

   Using the extension defined herein, an IP device can explicitly
   identify by the above the outgoing interface and next-hop over which
   a datagram would have been forwarded if that datagram had been
   deliverable.  This can be used for creating a downstream map.

   The extensions defined herein use the ICMP multi-part message
   framework defined in [RFC4884].  The same backward compatibility
   issues that apply to [RFC4884] apply to these extensions.


3.  Applications

3.1.  Application to TRACEROUTE

   ICMP extensions defined in this memo require enhancements ([RFC4884])
   and provide additional capability 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 triggering packet arrived,
   even when that interface is unnumbered.

3.2.  Policy and MTU Detection

   A general application would be to identify which outgoing interface
   triggered a given function for the original packet.  For example, if



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   an ACL drops the packet and Dest Unreachable/Admin Prohibited denies
   the packet, being able to identify that might be useful.  Another
   example would be support PMTU, since this would allow identification
   of which outgoing interface can't support a given MTU size.


4.  Interface Information Object

   This section defines an ICMP extension object that can be appended to
   the ICMPv4 Time Exceeded, ICMPv4 Destination Unreachable, ICMPv4
   Parameter Problem, ICMPv6 Time Exceeded, and ICMPv6 Destination
   Unreachable messages, as described in [RFC4884].  For the description
   of the Interface Information Object, the incoming interface is the
   one upon which the packet which triggered the ICMP message was
   received.  If desired, information about a sub-IP member of the
   incoming interface can be included.  An example of such a sub-IP
   member would be a member of an Ethernet Link Aggregation Group that
   forms the incoming interface.  To minimize the use of extra octets
   required for this extension, there are four different pieces of
   information that can appear in an Interface Information Object.

   1.  If the interface of interest has at least one IPv4 address and
       the triggering packet was IPv4, then one of the interface's IPv4
       addresses MAY be included.
   2.  If the interface of interest has at least one IPv6 address and
       the triggering packet was IPv6, then one of the interface's IPv6
       addresses MAY be included.
   3.  The ifIndex of the interface of interest MAY be included.  This
       is the ifIndex assigned to the interface by the router in as
       specified by the Interfaces Group MIB [RFC2863].
   4.  An Interface Name Sub-Object, containing a string of no more than
       62 octets, MAY be included.

4.1.  C-type meaning in an Interface Information Object

   For this object, the c-type is split into two fields, a 2-bit
   interface-role field and a 6-bit included-information field.  This is
   illustrated below.













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   Bit   7     6      |   5       4       3       2       1       0
      +-------+-------+-------+-------+-------+-------+-------+-------+
      | Interface Role| Rsvd  | Rsvd  | index | IP    | Rsvd  | descr |
      +-------+-------+-------+-------+-------+-------+-------+-------+

     Interface Role: This 2-bit field [6:7] indicates the role of the
                     interface being identified.  The enumerated values
                     are given below.
              0 : This object describes the incoming interface.
              1 : This object describes the outgoing interface.
              2 : This object describes a sub-IP member of the
                  incoming interface.
              3 : Reserved

     Included Information: This 6-bit field [0:5] indicates what
                        information is included in the object.  The
                        information must be included in the same order
                        as the bits (leftmost, from highest, 5, to
                        lowest, 0,).

      bit
       5 : This bit is reserved for future use and MUST be set to 0 and
           MUST be ignored on receipt.

       4 : This bit is reserved for future use and MUST be set to 0 and
           MUST be ignored on receipt.

       3 : When set, this bit indicates the ifIndex of the interface
           is included.  When clear, the ifIndex is not included.

       2 : When set, this indicates an IP address of the interface
           is included.  When clear, no IP address is included.  The
           version of the IP packet containing the ICMP message will
           indicate the type of IP address.  An IPv4 packet will have an
           IPv4 address and an IPv6 packet will have an IPv6 address.

       1 : This bit is reserved for future use and MUST be set to 0 and
           MUST be ignored on receipt.

       0 : When set, this indicates an Interface Name Sub-object for
           the interface is included.  When clear, it is not included.


           Figure 1: C-Type for the Interface Information Object

   The information/sub-objects MUST be sent and received inside the
   Interface Information Object in the order that they are listed in the
   final 6-bits included-information field.  With the exception of the



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   Interface Name sub-object, the information included does not self-
   identify, so this is required to ensure correct parsing.

   The sender of an Interface Information Object MUST NOT set the
   Interface Role to 3 and an Interface Role value of 3 MUST be ignored
   on receipt and the Interface Information Object discarded.  It is
   valid (though pointless until additional bits are assigned by IANA)
   to receive an Interface Information Object where bits 3,2, and 0 are
   all 0; this MUST NOT generate a warning or error.

4.2.  Interface Name Sub-Object

   The Interface Name Sub-Object MUST have a length that is a multiple
   of 4 octets and MUST NOT exceed 64 octets.  A one octet "charset
   type" and a one octet "length" are required and the interface name
   can be at most 62 octets long.  The interface name SHOULD be the
   MIB-II ifName [RFC2863] but MAY be some other human-meaningful name
   of the interface.  It is useful to rovide the ifName for cross-
   correlation with other MIB information and for human-reader
   familiarity.

   The Interface Name Sub-Object consists of three fields.  The first
   1-octet field indicates the character set type used by the second
   field.  The second field contains the length of the Interface name
   Sub-object, including the charset type, the length, and the human-
   readable name in octets.  The maximum valid length is 64 octets.  The
   length is constrained to ensure there is space for the start of the
   original packet and additional information.  The third field contains
   the human-readable name.

   octet      0          1        2                   63
        +--------------+--------+---..............-----------------+
        | charset type | length |   interface name octets 1-62     |
        +--------------+--------+---..............-----------------+


                    Figure 2: Interface Name Sub-Object

   charset type 0 : This indicates that the human-readable interface
   name MUST be provided in the US-ASCII charset [US-ASCII] using the
   Default Language [RFC2277].

   charset type 1 : This indicates that the human-readable interface
   name MUST be provided in the UTF-8 charset [RFC3629] using the
   Default Language [RFC2277].






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4.3.  Interface Information Object Description

   Figure 3 shows a full ICMPv4 Time Exceeded message, including the
   Interface Information Object, which must be preceded by an ICMP
   Extension Structure Header and an ICMP Object Header.  Both are
   defined in [RFC4884].

   Figure 4 depicts the Interface Information Object, with two of the
   valid permutations.

   Although all examples show an Interface Name Sub-object of length 64,
   this is only for illustration and depicts the maximum allowable
   length.


     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      |     Code      |          Checksum             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     unused    |    Length     |          unused               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Internet Header + leading octets of original datagram    |
     |                                                               |
     |                           //                                  |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Ver=2 |      (Reserved)       |           Checksum            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Length            |   Class-Num=2 | C-Type=9      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Interface ifIndex                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                Interface Name, 32-bit word 1                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...                                                              ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                Interface Name , 32-bit word 16                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


     Figure 3: ICMPv4 Time Exceeded message with Interface Information
                                  Object


             Class-Num = 2

     Example 1: Unnumbered Interface with ifIndex and interface name



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             C-Type = 00001001b   // Indicates incoming interface
             Length = 40 (4 + 4 + 32)

              0             1             2            3
      +--------------+--------------+--------------+--------------+
      |                    Interface ifIndex                      |
      +--------------+--------------+--------------+--------------+
      |                Interface Name, 32-bit word 1              |
      +--------------+--------------+--------------+--------------+
     ...                                                         ...
      +--------------+--------------+--------------+--------------+
      |                Interface Name , 32-bit word 16             |
      +--------------+--------------+--------------+--------------+


     Example 2: IPv4 interface with IPv4 address,
                ifIndex and interface name

             C-Type = 00001101b   // Indicates incoming interface
             Length = 44 (4 + 4 + 4 + 32)

              0             1             2            3
      +--------------+--------------+--------------+--------------+
      |                    Interface ifIndex                      |
      +--------------+--------------+--------------+--------------+
      |                    IPv4 address                           |
      +--------------+--------------+--------------+--------------+
      |                Interface Name, 32-bit word 1              |
      +--------------+--------------+--------------+--------------+
     ...                                                         ...
      +--------------+--------------+--------------+--------------+
      |                Interface Name, 32-bit word 16             |
      +--------------+--------------+--------------+--------------+


     Example 3: IPv6 interface with IPv6 address and ifIndex

             C-Type = 00001100b   // Indicates incoming interface
             Length = 24 (4 + 4 + 16)

              0             1             2            3
      +--------------+--------------+--------------+--------------+
      |                    Interface ifIndex                      |
      +--------------+--------------+--------------+--------------+
      |                    IPv6 address, 32-bit word 1            |
      +--------------+--------------+--------------+--------------+
      |                    IPv6 address, 32-bit word 2            |
      +--------------+--------------+--------------+--------------+



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      |                    IPv6 address, 32-bit word 3            |
      +--------------+--------------+--------------+--------------+
      |                    IPv6 address, 32-bit word 4            |
      +--------------+--------------+--------------+--------------+


                  Figure 4: Interface Information Object

4.4.  Usage

   For each interface described by an included Interface Information
   Object, these are the rules for the information to be included.  If
   the interface in question is unnumbered, then the Interface
   Information Object SHOULD include the ifIndex and SHOULD NOT include
   an IP address.  If the interface in question is numbered, then the
   Interface Information Object SHOULD include the IP address.  Other
   fields MAY be included in the Interface Information Object.

   In an ICMP message, more than one Interface Information Object with a
   given interface role MUST NOT be included.  Multiple Interface
   Information Objects, each with a different interface role, MAY be
   included.


5.  Security Considerations

   This extension 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 sub-objects to include
   based upon the destination IP address of the ICMP message that will
   contain the sub-objects.

   For instance, the IP address may be included for all potential
   recipients.  The ifIndex and interface name could be included as well
   if the destination IP address is a management address of the network
   that has administrative control of the router.

   Another example use case would be where the detailed information in
   these extensions may be provided to ICMP destinations within the
   local administrative domain, but only traditional information is
   provided to 'external' or untrusted ICMP destinations.

   Another issue is when a device inside a private region generates an
   ICMP message with some of these extensions and that ICMP message will
   transit a NAT to reach its destination.  A NAT may choose to remove
   or overwrite the extensions.



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6.  IANA Considerations

   IANA should should reserve from the ICMP Extension Object registry: 2
   for the Interface Information Object.

   From the Interface ID Object's c-type, IANA should reserve as
   follows:

   o  Bit 0: Interface Name Sub-Object included
   o  Bit 1: Unallocated - allocatable with Standards Action
   o  Bit 2: IP address included
   o  Bit 3: ifIndex include
   o  Bit 4: Unallocated - allocatable with Standards Action
   o  Bit 5: Unallocated - allocatable with Standards Action
   o  Bit 6-7: Interface Role field
      *  Value 0: Incoming Interface
      *  Value 1: Outgoing Interface
      *  Value 2: Incoming Interface - Sub-IP Member
      *  Value 3: Unallocated - allocatable with Standards Action

   Additionally, the Interface Name Sub-Object has a 1 octet charset
   type field.  IANA should create a registry for it and allocate as
   follows:

   o  0 : encoded in ASCII
   o  1 : encoded in UTF-8
   o  2-127: Unallocated - allocatable with Standards Action
   o  128-255: Unallocated - allocated on first come basis.


7.  Acknowledgements

   The authors would like to thank Carlos Pignataro, Sasha Vainshtein,
   and Joe Touch for their comments and suggestions.


8.  References

8.1.  Normative References

   [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.

   [RFC2863]  McCloghrie, K. and F. Kastenholz, "The Interfaces Group
              MIB", RFC 2863, June 2000.



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   [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.

   [RFC4884]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
              "Extended ICMP to Support Multi-Part Messages", RFC 4884,
              April 2007.

8.2.  Informative References

   [RFC1812]  Baker, F., "Requirements for IP Version 4 Routers",
              RFC 1812, June 1995.

   [RFC2277]  Alvestrand, H., "IETF Policy on Character Sets and
              Languages", BCP 18, RFC 2277, January 1998.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [US-ASCII]
              "Coded Character Set -- 7-bit American Standard Code for
              Information Interchange, ANSI X3.4-1986".


Authors' Addresses

   Alia K. Atlas (editor)
   BT

   Email: alia.atlas@bt.com


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

   Email: rbonica@juniper.net


   J.R. Rivers
   Nuova Systems

   Email: jrrivers@nuovasystems.com






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   Naiming Shen
   Cisco Systems
   225 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: naiming@cisco.com


   Enke Chen
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: enkechen@cisco.com



































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Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   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
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
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Acknowledgment

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





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