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Versions: 00 01 02 03 rfc5889                                           
Autoconf                                                E. Baccelli, Ed.
Internet-Draft                                                     INRIA
Intended status: Informational                          M. Townsley, Ed.
Expires: April 22, 2010                                    Cisco Systems
                                                        October 19, 2009


                 IP Addressing Model in Ad Hoc Networks
                draft-ietf-autoconf-adhoc-addr-model-00

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on April 22, 2010.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
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   This document is subject to BCP 78 and the IETF Trust's Legal
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Abstract

   This document describes a model for configuring IP addresses and
   subnet prefixes on the interfaces of routers which connect to links



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   with undetermined connectivity properties.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Applicability Statement . . . . . . . . . . . . . . . . . . . . 3
   4.  IP Subnet Prefix Configuration  . . . . . . . . . . . . . . . . 3
   5.  IP Address Configuration  . . . . . . . . . . . . . . . . . . . 4
   6.  Addressing Model  . . . . . . . . . . . . . . . . . . . . . . . 4
     6.1.  IPv4 Model  . . . . . . . . . . . . . . . . . . . . . . . . 5
     6.2.  IPv6 Model  . . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Appendix A.  Open Issues  . . . . . . . . . . . . . . . . . . . . . 6
   Appendix B.  Contributors . . . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
































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1.  Introduction

   The appropriate configuration of IP addresses and subnet masks for
   router network interfaces is generally a prerequisite to the correct
   functioning of routing protocols.  Consideration of various items,
   including underlying link capabilities and connectivity, geographical
   topology, available address blocks, assumed traffic patterns,
   etc. are used when determining the appropriate network topology and
   the associated IP interface configuration.

   When the capabilities and connectivity of the links that connect
   routers are well-known and rather stable, logical network topology
   design and corresponding IP interface configuration are rather
   straightforward.  Absent any assumption about link-level
   connectivity, there is no canonical method for determining a given IP
   interface configuration.

   Ad hoc networks are typical examples of networks with undetermined
   link-level connectivity.  MANET routing protocols have as purpose to
   detect and maintain network connectivity, assuming that routers'
   interfaces are configured with IP addresses.  This document thus
   proposes a model for configuration of IP addresses and subnet
   prefixes on router interfaces to links with undetermined connectivity
   properties.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119].


3.  Applicability Statement

   The configuration proposed by this model is applicable to any
   router's IP interface.  It specifies IP addresses and IP subnet
   prefixes to be configured on network interfaces.

   When more specific assumptions can be made regarding the connectivity
   between interfaces, these SHOULD be considered when configuring
   subnet prefixes.


4.  IP Subnet Prefix Configuration

   If the link to which an interface connects enables no assumptions of



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   connectivity to other interfaces, the only addresses which can be
   assumed "on link", are the address(es) of that interface itself.
   Note that while link-local addresses are assumed to be "on link", the
   utility of link-local addresses is limited as described in Section 6.

   Subnet prefix configuration on such interfaces must thus not make any
   promises in terms of direct (one hop) IP connectivity to IP addresses
   other than that of the interface itself.  This suggests the following
   principle:

   o  no two such interfaces in the network should be configured with
      the same subnet prefix.

   If L2 communication is enabled between a pair of interfaces, IP
   packet exchange is enabled regardless of the IP subnet configuration
   on each of these interfaces.

   If on the contrary, assumptions can be made regarding connectivity
   between interfaces, these SHOULD be considered when configuring IP
   subnet prefixes, and the corresponding interfaces MAY be configured
   with the same subnet prefix.


5.  IP Address Configuration

   Routing protocols running on a router may exhibit different
   requirements for uniqueness of interface addresses; some have no such
   requirements, others have requirements ranging from local uniqueness
   only, to uniqueness within, at least, the routing domain.

   Configuring an IP address that is unique within the routing domain
   satisfies the less stringent uniqueness requirements of local
   uniqueness, while also enabling protocols which have the most
   stringent requirements of uniqueness within the routing domain.  This
   suggests the following principle:

   o  an IP address assigned to an interface that connects to a link
      with undetermined connectivity properties should be unique, at
      least within the routing domain.


6.  Addressing Model

   Section 4 and Section 5 describe principles for IP address and subnet
   prefix configuration on an interface of a router, when that interface
   connects to a link with undetermined connectivity properties.  The
   following describes guidelines that follow from these  principles,
   respectively for IPv4 and IPv6.



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6.1.  IPv4 Model

   For IPv4, the principles described in Section 4 and Section 5 suggest
   the following rules:

   o  An IP address configured on this interface should be unique, at
      least within the routing domain; and

   o  Any subnet prefix configured on this interface should be of length
      /32.

   Note that the use of IPv4 link-local addresses [RFC3927] in this
   context should be discouraged for most applications, as the
   limitations outlined in Section 6.2 for IPv6 link-local addresses
   also concern IPv4 link-local addresses.  These limitations are
   further exacerbated by the smaller pool of IPv4 link-local addresses
   to choose from and thus increased reliance on DAD.

6.2.  IPv6 Model

   For IPv6, the principles described in Section 4 and Section 5 suggest
   the following rules:

   o  An IP address configured on this interface should be unique, at
      least within the routing domain, and

   o  A subnet prefix configured on this interface should be of length
      /128.

   Note that while an IPv6 link-local address is assigned to each
   interface as per [RFC4291], in general link-local addresses are of
   limited utility on links with undetermined connectivity, as
   connnectivity to neighbors may be constantly changing.  The known
   limitations are:

   o  Even if tested for local uniqueness at one moment using
      Duplicate Address Detection [RFC4862], a duplicate link-local
      address might appear as a neighbor the next moment, without it
      being an explicit event that would trigger DAD again.  Such
      duplication would thus go undetected.

   o  There is no mechanism to ensure that IPv6 link-local addresses are
      unique across multiple links, hence they can not be used to
      reliably identify routers.

   o  Routers cannot forward any packets with link-local source or
      destination addresses to other links (as per [RFC4291]) while most
      of the time, routers need to be able to forward packets to/from



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      different links.

   Therefore MANET autoconfiguration solutions should be encouraged to
   primarily focus on configuring IP addresses that are not IPv6 link-
   local.


7.  IANA Considerations

   This document has no actions for IANA.


8.  Security Considerations

   This document does currently not describe any security
   considerations.


9.  Normative References

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

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, 2006.

   [RFC3927]  Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
              Configuration of IPv4 Link-Local Addresses", RFC 3927,
              2005.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, 2007.


Appendix A.  Open Issues

   The following issues were extensively discussed among the design
   team, without reaching a conclusion.

   MANET Link Model -  no satisfying MANET link model was formulated to
      date.  Lacking a better definition so far, a MANET link is: a link
      with undetermined connectivity properties.

   Global Uniqueness Requirements -  it remains to be determined whether
      or not the scope of AUTOCONF includes applications other than
      routing protocols running on the router, which may communicate
      with outside the routing domain and which for that, require
      globally unique addresses.



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Appendix B.  Contributors

   This document reflects discussions and contributions from several
   individuals including (in alphabetical order):

   Teco Boot: teco@inf-net.nl

   Ulrich Herberg: ulrich@herberg.name

   Thomas Narten: narten@us.ibm.com

   Charles Perkins: charliep@computer.org

   Erik Nordmark: erik.nordmark@sun.com


Authors' Addresses

   Emmanuel Baccelli
   INRIA

   Email: Emmanuel.Baccelli@inria.fr
   URI:   http://www.emmanuelbaccelli.org/


   Mark Townsley
   Cisco Systems

   Email: townsley@cisco.com






















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