1. RFC 6745
Internet Research Task Force (IRTF)                          RJ Atkinson
Request for Comments: 6745                                    Consultant
Category: Experimental                                         SN Bhatti
ISSN: 2070-1721                                            U. St Andrews
                                                           November 2012

                  ICMP Locator Update Message for the
         Identifier-Locator Network Protocol for IPv4 (ILNPv4)


   This note defines an experimental ICMP message type for IPv4 used
   with the Identifier-Locator Network Protocol (ILNP).  ILNP is an
   experimental, evolutionary enhancement to IP.  The ICMP message
   defined herein is used to dynamically update Identifier/Locator
   bindings for an existing ILNP session.  This is a product of the IRTF
   Routing Research Group.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Research Task
   Force (IRTF).  The IRTF publishes the results of Internet-related
   research and development activities.  These results might not be
   suitable for deployment.  This RFC represents the individual
   opinion(s) of one or more members of the Routing Research Group of
   the Internet Research Task Force (IRTF).  Documents approved for
   publication by the IRSG are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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Copyright Notice

   Copyright (c) 2012 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
   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.

   This document may not be modified, and derivative works of it may not
   be created, except to format it for publication as an RFC or to
   translate it into languages other than English.

Table of Contents

   1. Introduction ....................................................2
      1.1. Document Roadmap ...........................................3
      1.2. ICMPv4 Locator Update ......................................4
      1.3. Terminology ................................................5
   2. ICMP Locator Update Message for ILNPv4 ..........................5
   3. Transport Protocol Effects ......................................8
   4. Implementation Considerations ...................................8
   5. Backwards Compatibility .........................................9
   6. Security Considerations .........................................9
   7. IANA Considerations ............................................10
   8. References .....................................................10
      8.1. Normative References ......................................10
      8.2. Informative References ....................................11
   9. Acknowledgements ...............................................11

1.  Introduction

   This document is part of the ILNP document set, which has had
   extensive review within the IRTF Routing RG.  ILNP is one of the
   recommendations made by the RG Chairs.  Separately, various refereed
   research papers on ILNP have also been published during this decade.
   So the ideas contained herein have had much broader review than the
   IRTF Routing RG.  The views in this document were considered
   controversial by the Routing RG, but the RG reached a consensus that
   the document still should be published.  The Routing RG has had
   remarkably little consensus on anything, so virtually all Routing RG
   outputs are considered controversial.

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   At present, the Internet research and development community is
   exploring various approaches to evolving the Internet Architecture to
   solve a variety of issues including, but not limited to, scalability
   of inter-domain routing [RFC4984].  A wide range of other issues
   (e.g., site multihoming, node multihoming, site/subnet mobility, node
   mobility) are also active concerns at present.  Several different
   classes of evolution are being considered by the Internet research
   and development community.  One class is often called "Map and
   Encapsulate", where traffic would be mapped and then tunnelled
   through the inter-domain core of the Internet.  Another class being
   considered is sometimes known as "Identifier/Locator Split".  This
   document relates to a proposal that is in the latter class of
   evolutionary approaches.

   The Identifier-Locator Network Protocol (ILNP) is a proposal for
   evolving the Internet Architecture.  It differs from the current
   Internet Architecture primarily by deprecating the concept of an IP
   Address and instead defining two new objects, each having crisp
   syntax and semantics.  The first new object is the Locator, a
   topology-dependent name for a subnetwork.  The other new object is
   the Identifier, which provides a topology-independent name for a

1.1.  Document Roadmap

   This document describes a new ICMPv4 Locator Update message used by
   an ILNP node to inform its correspondent nodes of any changes to its
   set of valid Locators.

   The ILNP architecture can have more than one engineering
   instantiation.  For example, one can imagine a "clean-slate"
   engineering design based on the ILNP architecture.  In separate
   documents, we describe two specific engineering instances of ILNP.
   The term "ILNPv6" refers precisely to an instance of ILNP that is
   based upon, and is backwards compatible with, IPv6.  The term
   "ILNPv4" refers precisely to an instance of ILNP that is based upon,
   and backwards compatible with, IPv4.

   Many engineering aspects common to both ILNPv4 and ILNPv6 are
   described in [RFC6741].  A full engineering specification for either
   ILNPv6 or ILNPv4 is beyond the scope of this document.

   Readers are referred to other related ILNP documents for details not
   described here:

   a) [RFC6740] is the main architectural description of ILNP, including
      the concept of operations.

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   b) [RFC6741] describes engineering and implementation considerations
      that are common to both ILNPv4 and ILNPv6.

   c) [RFC6742] defines additional DNS resource records that support

   d) [RFC6743] defines a new ICMPv6 Locator Update message used by an
      ILNP node to inform its correspondent nodes of any changes to its
      set of valid Locators.

   e) [RFC6744] defines a new IPv6 Nonce Destination Option used by
      ILNPv6 nodes (1) to indicate to ILNP correspondent nodes (by
      inclusion within the initial packets of an ILNP session) that the
      node is operating in the ILNP mode and (2) to prevent off-path
      attacks against ILNP ICMP messages.  This Nonce is used, for
      example, with all ILNP ICMPv6 Locator Update messages that are
      exchanged among ILNP correspondent nodes.

   f) [RFC6746] defines a new IPv4 Nonce Option used by ILNPv4 nodes to
      carry a security nonce to prevent off-path attacks against ILNP
      ICMP messages, and it also defines a new IPv4 Identifier Option
      used by ILNPv4 nodes.

   g) [RFC6747] describes extensions to Address Resolution Protocol
      (ARP) for use with ILNPv4.

   h) [RFC6748] describes optional engineering and deployment functions
      for ILNP.  These are not required for the operation or use of ILNP
      and are provided as additional options.

1.2.  ICMPv4 Locator Update

   As described in [RFC6740] and [RFC6741], an ILNP for IPv4 (ILNPv4)
   node might need to inform correspondent ILNPv4 nodes of changes to
   the set of valid Locator values.  The new ICMPv4 Locator Update
   message described in this document enables an ILNP-capable node to
   update its correspondents about the currently valid set of Locators
   valid to use in reaching the node sending this message [RFC2460]

   This new ICMPv4 message MUST ONLY be used for ILNPv4 sessions.
   Authentication is always required, as described in the Security
   Considerations section later in this document.

   Some might consider any and all use of ICMP to be undesirable.

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   In that context, please note that while this specification uses ICMP,
   on grounds that this is a control message, there is no architectural
   difference between using ICMP and using some different framing, for
   example UDP.

1.3.  Terminology

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

2.  ICMP Locator Update Message for ILNPv4

   The ICMP for IPv4 message described in this section has ICMP Type 253
   (as defined for experimental use in Section 8 of [RFC4727]) and is
   used ONLY with a current ILNPv4 session.  This message enables an
   ILNPv4 node to advertise changes to the active Locator set for the
   ILNPv4 node that originates this message to its unicast ILNP
   correspondent nodes.  It also enables those correspondents to
   acknowledge receipt of the advertisement.

   This particular ICMP for IPv4 message MUST ONLY be used with ILNPv4
   sessions.  The Checksum field for this message is calculated
   identically as for any other IPv4 ICMP message.

   ICMP Locator Update message

       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            |
      |  Num of Locs  |   Operation   |           RESERVED            |
      /                       Locator [1]                             /
      |        Preference [1]         |           Lifetime [1]        |
      /                       Locator [2]                             /
      |        Preference [2]         |           Lifetime [2]        |

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      ICMP Fields:

         Type                  253
                               This type value is taken from Section 8
                               of [RFC4727] and is allocated for
                               experimental use.

         Code                  0

         Checksum              The  16-bit one's complement of the
                               one's complement sum of the ICMP
                               message, starting with the ICMP Type.
                               For computing the checksum, the
                               Checksum field is set to 0.

         Num of Locs           The number of 32-bit Locator values
                               that are advertised in this message.

         Locator[i],           The 32-bit Locator values currently
          i = 1..Num of Locs   valid for the sending ILNPv4 node.

         Preference[i],        The preferability of each Locator[i],
          i = 1..Num of Locs   relative to other valid Locator[i]
                               values.  The Preference numbers here
                               are identical, both in syntax and
                               semantics, to the Preference values
                               for L32 records that are specified by

         Lifetime[i]           The maximum number of seconds that this
          i = 1..Num of Locs   particular Locator may be considered
                               valid.  Normally, this is identical
                               to the DNS lifetime of the
                               corresponding L32 record, if one

          Operation            The value in this field indicates
                               whether this is a Locator Update
                               Advertisement (0x01) or a Locator
                               Update Acknowledgement (0x02).

          RESERVED             A field reserved for possible future
                               use.  At present, the sender MUST
                               initialise this field to zero.
                               Receivers should ignore this field at
                               present.  The field might be used for
                               some protocol function in future.

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   NOTE WELL:  The ICMP Type value is allocated for shared
               experimental use in Section 8 of [RFC4727].
               It is not uniquely assigned to ILNPv4.  So,
               implementations need to code particularly
               defensively as other IPv4 experiments might be
               using this same ICMP Type value for an
               entirely different purpose with a different
               ICMP packet format.

   The Operation field has value 1 (hexadecimal 0x01) for a Locator
   Update Advertisement.  The Operation field has value 2 (hexadecimal
   0x02) for a Locator Update Acknowledgement.  All other values of the
   Operation field are reserved for future use by future revisions of
   this specification.

   A node whose set of valid Locators has changed MUST send Locator
   Update Advertisement messages to each correspondent node for each
   active unicast ILNP session.  For unicast ILNP sessions, the receiver
   of a valid (i.e., authentication checks all passed, advertisement is
   received from a current correspondent node) Locator Update
   Advertisement addressed to the receiver MUST send a Locator Update
   Acknowledgement back to the sender of the Locator Update
   Advertisement.  The Acknowledgement message body is identical to the
   received Advertisement message body, except for the Operation value.

   All ILNPv4 ICMP Locator Update messages MUST contain a valid ILNPv4
   Identifier Option and MUST contain an ILNPv4 Nonce Option.

   ILNPv4 ICMP Locator Update messages also MAY be protected using IP
   Security for ILNP [RFC6741] [RFC4301].  Deployments in high-threat
   environments SHOULD also protect ILNPv4 ICMP Locator Update messages
   using IPsec.  While IPsec Encapsulating Security Payload (ESP) can
   protect a payload, no form of IPsec ESP is able to protect an IPv4
   Option that appears prior to the ESP header.  Note that even when IP
   Security for ILNP is in use, the ILNPv4 Nonce Option still MUST be
   present.  This simplifies protocol processing, and it also means that
   a receiver can perform the inexpensive check of the Nonce value
   before performing any (potentially expensive) cryptographic

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3.  Transport Protocol Effects

   The ICMP Locator Update message has no impact on any transport

   The ICMP Locator Update message might affect where packets for a
   given transport-layer session are sent, but an ILNP design objective
   is to decouple transport protocols (e.g., TCP, UDP, SCTP) and
   transport-layer sessions network-layer changes.

4.  Implementation Considerations

   Implementers may use any internal implementation they wish, provided
   that the external appearance is the same as this implementation

   To support ILNPv4, and to retain the incremental deployability and
   backwards compatibility needed, the network layer needs a mode bit in
   the Transport Control Block (or its equivalent) to track which IP
   sessions are using the classic IPv4 mode and which IP sessions are
   using ILNPv4 mode.

   Further, when supporting ILNPv4, nodes will need to support a
   Identifier Locator Communication Cache (ILCC) in the network layer as
   described in [RFC6741].

   A node sending an ICMP Locator Update message MUST include all
   currently valid Locator values in that message.  A node receiving a
   valid ICMP Locator Update message MUST replace the previously current
   set of Locator values for that correspondent node in its own ILCC
   with the newly received set of Locator values.

   Every implementation needs to support a large number of Locator
   values being sent or received in a single ICMP Locator Update
   message, because a multihomed node or multihomed site might have a
   large number of upstream links to different service providers, each
   with its own Locator value.

   It should be noted that as the ICMP Type uses an experimental value
   from [RFC4727], care should be taken when using with other protocols
   also using experimental values.

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5.  Backwards Compatibility

   This IPv4 ICMP message uses the same checksum calculations as any
   other IPv4 ICMP message.

   When ILNPv4 is not in use, the receiving IPv4 mode MUST discard the
   ICMP Locator Update packet without processing the packet.

6.  Security Considerations

   Security considerations for the overall ILNP Architecture are
   described in [RFC6740].  Additional common security considerations
   are described in [RFC6741].  This section describes security
   considerations specific to ILNPv4 topics discussed in this document.

   The ICMPv4 Locator Update message MUST ONLY be used for ILNPv4

   The ILNPv4 Nonce Option [RFC6746] MUST be present in packets
   containing an ICMPv4 Locator Update message.  Further, the received
   Nonce Destination Option must contain the correct nonce value for the
   packet to be accepted by the recipient and then passed to the ICMPv4
   protocol for processing.  If either of these requirements are not
   met, the received packet MUST be discarded as a forgery, and a
   security event SHOULD be logged by the system receiving the non-
   authentic packet.

   ILNP sessions operating in higher risk environments SHOULD use IP
   Security for ILNP [RFC6741] [RFC4301] *in addition* to the ILNPv4
   Nonce Option.  Use of IP Security for ILNP to protect a packet does
   NOT permit the packet to be sent without the Nonce Option.

   Implementations need to support the case where a single ICMP Locator
   Update message contains a large number of Locator and Preference
   values and ought not develop a security fault (e.g., stack overflow)
   due to a received message containing more Locator values than

   If the ILNP Nonce value is predictable, then an off-path attacker
   might be able to forge data or control packets.  This risk also is
   mitigated by the existing common practice of IP Source Address
   filtering [RFC2827] [RFC3704].

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7.  IANA Considerations

   This document makes no request of IANA.

   If in the future the IETF decided to standardise ILNPv4, then
   allocation of a unique ICMP Type for the Locator Update as part of
   the IETF standardisation process would be sensible.

8.  References

8.1.  Normative References

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

   [RFC2460]   Deering, S. and R. Hinden, "Internet Protocol, Version 6
               (IPv6) Specification", RFC 2460, December 1998.

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

   [RFC4301]   Kent, S. and K. Seo, "Security Architecture for the
               Internet Protocol", RFC 4301, December 2005.

   [RFC4727]   Murphy, S., "BGP Security Vulnerabilities Analysis", RFC
               4272, January 2006.

   [RFC6740]   Atkinson, R. and S. Bhatti, "Identifier-Locator Network
               Protocol (ILNP) Architectural Description", RFC 6740,
               November 2012.

   [RFC6747]   Atkinson, R. and S. Bhatti, "Address Resolution Protocol
               (ARP) Extension for the Identifier-Locator Network
               Protocol for IPv4 (ILNPv4)", RFC 6747, November 2012.

   [RFC6741]   Atkinson, R. and S. Bhatti, "Identifier-Locator Network
               Protocol (ILNP) Engineering and Implementation
               Considerations", RFC 6741, November 2012.

   [RFC6746]   Atkinson, R. and S.Bhatti, "IPv4 Options for the
               Identifier-Locator Network Protocol (ILNP)", RFC 6746,
               November 2012.

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8.2.  Informative References

   [RFC2827]   Ferguson, P. and D. Senie, "Network Ingress Filtering:
               Defeating Denial of Service Attacks which employ IP
               Source Address Spoofing", BCP 38, RFC 2827, May 2000.

   [RFC3704]   Baker, F. and P. Savola, "Ingress Filtering for
               Multihomed Networks", BCP 84, RFC 3704, March 2004.

   [RFC4984]   Meyer, D., Ed., Zhang, L., Ed., and K. Fall, Ed., "Report
               from the IAB Workshop on Routing and Addressing", RFC
               4984, September 2007.

   [RFC6742]   Atkinson, R., Bhatti, S. and S. Rose, "DNS Resource
               Records for the Identifier-Locator Network Protocol
               (ILNP)", RFC 6742, November 2012.

   [RFC6748]   Atkinson, R. and S. Bhatti, "Optional Advanced Deployment
               Scenarios for the Identifier-Locator Network Protocol
               (ILNP)", RFC 6748, November 2012.

   [RFC6743]   Atkinson, R. and S. Bhatti, "ICMPv6 Locator Update
               Message", RFC 6743, November 2012.

   [RFC6744]   Atkinson, R. and S. Bhatti, "IPv6 Nonce Destination
               Option for the Identifier-Locator Network Protocol for
               IPv6 (ILNPv6)", RFC 6744, November 2012.

9.  Acknowledgements

   Steve Blake, Stephane Bortzmeyer, Mohamed Boucadair, Noel Chiappa,
   Wes George, Steve Hailes, Joel Halpern, Mark Handley, Volker Hilt,
   Paul Jakma, Dae-Young Kim, Tony Li, Yakov Rehkter, Bruce Simpson,
   Robin Whittle, and John Wroclawski (in alphabetical order) provided
   review and feedback on earlier versions of this document.  Steve
   Blake provided an especially thorough review of an early version of
   the entire ILNP document set, which was extremely helpful.  We also
   wish to thank the anonymous reviewers of the various ILNP papers for
   their feedback.

   Roy Arends provided expert guidance on technical and procedural
   aspects of DNS issues.

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Authors' Addresses

   RJ Atkinson
   San Jose, CA 95125

   EMail: rja.lists@gmail.com

   SN Bhatti
   School of Computer Science
   University of St Andrews
   North Haugh, St Andrews
   Fife  KY16 9SX
   Scotland, UK

   EMail: saleem@cs.st-andrews.ac.uk

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  1. RFC 6745