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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]
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+RFC 5889 Ad Hoc IP Addressing September 2010
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+ 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.
+
+
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+
+
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+Baccelli & Townsley Informational [Page 4]
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+RFC 5889 Ad Hoc IP Addressing September 2010
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+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]
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+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]
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+RFC 5889 Ad Hoc IP Addressing September 2010
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+
+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]
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+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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