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+Internet Engineering Task Force (IETF)                  E. Baccelli, Ed.
+Request for Comments: 5889                                         INRIA
+Category: Informational                                 M. Townsley, Ed.
+ISSN: 2070-1721                                            Cisco Systems
+                                                          September 2010
+
+
+                 IP Addressing Model in Ad Hoc Networks
+
+Abstract
+
+   This document describes a model for configuring IP addresses and
+   subnet prefixes on the interfaces of routers which connect to links
+   with undetermined connectivity properties.
+
+Status of This Memo
+
+   This document is not an Internet Standards Track specification; it is
+   published for informational purposes.
+
+   This document is a product of the Internet Engineering Task Force
+   (IETF).  It represents the consensus of the IETF community.  It has
+   received public review and has been approved for publication by the
+   Internet Engineering Steering Group (IESG).  Not all documents
+   approved by the IESG are 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
+   http://www.rfc-editor.org/info/rfc5889.
+
+Copyright Notice
+
+   Copyright (c) 2010 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.  Code Components extracted from this document must
+   include Simplified BSD License text as described in Section 4.e of
+   the Trust Legal Provisions and are provided without warranty as
+   described in the Simplified BSD License.
+
+
+
+
+
+
+Baccelli & Townsley           Informational                     [Page 1]
+
+RFC 5889                  Ad Hoc IP Addressing            September 2010
+
+
+Table of Contents
+
+   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
+   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
+   3.  Applicability Statement . . . . . . . . . . . . . . . . . . . . 4
+   4.  IP Subnet Prefix Configuration  . . . . . . . . . . . . . . . . 4
+   5.  IP Address Configuration  . . . . . . . . . . . . . . . . . . . 4
+   6.  Addressing Model  . . . . . . . . . . . . . . . . . . . . . . . 5
+     6.1.  IPv6 Model  . . . . . . . . . . . . . . . . . . . . . . . . 5
+     6.2.  IPv4 Model  . . . . . . . . . . . . . . . . . . . . . . . . 6
+   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
+   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
+     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
+     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
+   Appendix A.  Contributors . . . . . . . . . . . . . . . . . . . . . 7
+
+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 stable, logical network topology design
+   and corresponding IP interface configuration are straightforward.
+   Absent any assumption about link-level connectivity, however, there
+   is no canonical method for determining a given IP interface
+   configuration.
+
+   Link-level connectivity is generally qualified as undetermined when
+   it is unplanned and/or time-varying in character.  Ad hoc networks
+   are typical examples of networks with undetermined link-level
+   connectivity.  Routing protocols for ad hoc networks are purposely
+   designed to detect and maintain paths across the network, even when
+   faced with links with undetermined 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, to allow routing protocols and data packet forwarding to
+   function.
+
+   Note that routers may ultimately need additional IP prefixes for the
+   diverse applications that could run directly on the routers
+   themselves, or for assignment to attached hosts or networks.  For
+
+
+
+Baccelli & Townsley           Informational                     [Page 2]
+
+RFC 5889                  Ad Hoc IP Addressing            September 2010
+
+
+   IPv6, these addresses may be global [RFC3587], Unique-Local [RFC4193]
+   or Link-Local [RFC4291].  For IPv4, the addresses may be global
+   (i.e., public) or private [RFC1918].  In general, global scope is
+   desired over local scope, though it is understood that this may not
+   always be achievable via automatic configuration mechanisms.  In this
+   document however, automatic configuration of the prefixes used for
+   general applications is considered as a problem that is separable
+   from that of automatic configuration of addresses and prefixes
+   necessary for routing protocols to function.  This document thus
+   focuses on the latter: the type of IP address and subnet mask
+   configuration necessary for routing protocols and data packet
+   forwarding to function.
+
+2.  Terminology
+
+   This document uses the vocabulary and the concepts defined in
+   [RFC1918] and [RFC4632] for IPv4, as well as [RFC4291] for IPv6.
+
+3.  Applicability Statement
+
+   This model gives guidance about the configuration of IP addresses and
+   the IP subnet prefixes on a router's IP interfaces, which connect to
+   links with undetermined connectivity properties.
+
+   When more specific assumptions can be made regarding the connectivity
+   between interfaces or the (persistent) reachability of some
+   addresses, 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
+   connectivity to other interfaces, the only addresses that 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.
+
+   Thus, subnet prefix configuration on such interfaces must 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 on-link subnet prefix should be configured on such an
+      interface.
+
+   Note that if layer 2 communication is enabled between a pair of
+   interfaces, IP packet exchange is also enabled, even if IP subnet
+   configuration is absent or different on each of these interfaces.
+
+
+
+Baccelli & Townsley           Informational                     [Page 3]
+
+RFC 5889                  Ad Hoc IP Addressing            September 2010
+
+
+   Also note that if, on the contrary, assumptions can be made regarding
+   the connectivity between interfaces, or regarding the persistent
+   reachability of some addresses, these should be considered when
+   configuring IP subnet prefixes, and the corresponding interface(s)
+   may in such case be configured with an on-link 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 (as defined
+   in [RFC1136]).
+
+   Routing protocols that do not require unique IP addresses within the
+   routing domain utilize a separate unique identifier within the
+   routing protocol itself; such identifiers could be based on factory
+   assignment or configuration.
+
+   Nevertheless, configuring an IP address that is unique within the
+   routing domain satisfies the less stringent uniqueness requirements,
+   while also enabling protocols that have the most stringent
+   requirements of uniqueness within the routing domain.  As a result,
+   the following principle allows for IP autoconfiguration to apply to
+   the widest array of routing protocols:
+
+   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
+
+   Sections 4 and 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 IPv6 and IPv4.
+
+   Note that the guidelines provided in this document slightly differ
+   for IPv6 and IPv4, as IPv6 offers possibilities that IPv4 does not
+   (i.e., the possibility to simply not configure any on-link subnet
+   prefix on an IPv6 interface), which provide a "cleaner" model.
+
+
+
+
+
+
+
+
+
+Baccelli & Townsley           Informational                     [Page 4]
+
+RFC 5889                  Ad Hoc IP Addressing            September 2010
+
+
+6.1.  IPv6 Model
+
+   For IPv6, the principles described in Sections 4 and 5 suggest the
+   following rules:
+
+   o  An IP address configured on this interface should be unique, at
+      least within the routing domain, and
+
+   o  No on-link subnet prefix is configured on this interface.
+
+   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
+   connectivity to neighbors may be constantly changing.  The known
+   limitations are:
+
+   o  In general, there is no mechanism to ensure that IPv6 link-local
+      addresses are unique across multiple links, though link-local
+      addresses using an IID that are of the modified EUI-64 form should
+      be globally unique.
+
+   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 different links.
+
+   Therefore, autoconfiguration solutions should be encouraged to
+   primarily focus on configuring IP addresses that are not IPv6 link-
+   local.
+
+6.2.  IPv4 Model
+
+   For IPv4, the principles described in Sections 4 and 5 suggest rules
+   similar to those mentioned for IPv6 in Section 6.1, that are:
+
+   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 32 bits
+      long.
+
+   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 6.1 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 Duplicate Address
+   Detection (DAD).
+
+
+
+Baccelli & Townsley           Informational                     [Page 5]
+
+RFC 5889                  Ad Hoc IP Addressing            September 2010
+
+
+7.  Security Considerations
+
+   This document focuses on the IP address and subnet mask configuration
+   necessary for routing protocols and data packet forwarding to
+   function.  [RFC4593] describes generic threats to routing protocols,
+   whose applicability is not altered by the presence of interfaces with
+   undetermined connectivity properties.  As such, the addressing model
+   described in this document does not introduce new security threats.
+
+   However, the possible lack of pre-established infrastructure or
+   authority, as enabled by the use of interfaces with undetermined
+   connectivity properties, may render some of the attacks described in
+   [RFC4593] easier to undertake.  In particular, detection of
+   malevolent misconfiguration may be more difficult to detect and to
+   locate.
+
+8.  References
+
+8.1.  Normative References
+
+   [RFC1136]  Hares, S. and D. Katz, "Administrative Domains and Routing
+              Domains: A model for routing in the Internet", RFC 1136,
+              December 1989.
+
+   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
+              Architecture", RFC 4291, February 2006.
+
+   [RFC3927]  Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
+              Configuration of IPv4 Link-Local Addresses", RFC 3927,
+              May 2005.
+
+   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
+              and E. Lear, "Address Allocation for Private Internets",
+              BCP 5, RFC 1918, February 1996.
+
+   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
+              Addresses", RFC 4193, October 2005.
+
+   [RFC3587]  Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global
+              Unicast Address Format", RFC 3587, August 2003.
+
+   [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
+              (CIDR): The Internet Address Assignment and Aggregation
+              Plan", BCP 122, RFC 4632, August 2006.
+
+
+
+
+
+
+
+Baccelli & Townsley           Informational                     [Page 6]
+
+RFC 5889                  Ad Hoc IP Addressing            September 2010
+
+
+8.2.  Informative References
+
+   [RFC4593]  Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to
+              Routing Protocols", RFC 4593, October 2006.
+
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+Baccelli & Townsley           Informational                     [Page 7]
+
+RFC 5889                  Ad Hoc IP Addressing            September 2010
+
+
+Appendix A.  Contributors
+
+   This document reflects discussions and contributions from several
+   individuals including (in alphabetical order): Teco Boot, Thomas
+   Clausen, Ulrich Herberg, Thomas Narten, Erik Nordmark, Charles
+   Perkins, Zach Shelby, and Dave Thaler.
+
+Authors' Addresses
+
+   Emmanuel Baccelli (editor)
+   INRIA
+
+   EMail: Emmanuel.Baccelli@inria.fr
+   URI:   http://www.emmanuelbaccelli.org/
+
+
+   Mark Townsley (editor)
+   Cisco Systems
+
+   EMail: mark@townsley.net
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+Baccelli & Townsley           Informational                     [Page 8]
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