Autoconf E. Baccelli, Ed. Internet-Draft INRIA Intended status: Informational M. Townsley, Ed. Expires: June 10, 2010 Cisco Systems December 7, 2009 IP Addressing Model in Ad Hoc Networks draft-ietf-autoconf-adhoc-addr-model-01 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 Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on June 10, 2010. Copyright Notice Copyright (c) 2009 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 Baccelli, Ed. & Townsley, Ed. Expires June 10, 2010 [Page 1] Internet-Draft Ad Hoc IP Addressing December 2009 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 BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 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. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 9. Normative References . . . . . . . . . . . . . . . . . . . . . 6 Appendix A. Changes since -00 . . . . . . . . . . . . . . . . . . 7 Appendix B. Contributors . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Baccelli, Ed. & Townsley, Ed. Expires June 10, 2010 [Page 2] Internet-Draft Ad Hoc IP Addressing December 2009 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 have as purpose 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 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 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 to function. 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and Baccelli, Ed. & Townsley, Ed. Expires June 10, 2010 [Page 3] Internet-Draft Ad Hoc IP Addressing December 2009 "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Moreover, this document uses the vocabulary and the concepts defined in [RFC1918] and [RFC4632] for IPv4, as well as [RFC4291] for IPv6. 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, 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 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 on-link subnet prefix should be configured on such an interface. 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 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 Baccelli, Ed. & Townsley, Ed. Expires June 10, 2010 [Page 4] Internet-Draft Ad Hoc IP Addressing December 2009 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 IPv6 and IPv4. 6.1. 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 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 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 different links. Baccelli, Ed. & Townsley, Ed. Expires June 10, 2010 [Page 5] Internet-Draft Ad Hoc IP Addressing December 2009 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 Section 4 and Section 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 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 6.1 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 DAD. 7. IANA Considerations This document has no actions for IANA. 8. Security Considerations This document does 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. [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., and E. Lear, "Address Allocation for Private Internets", RFC 1918, 1996. Baccelli, Ed. & Townsley, Ed. Expires June 10, 2010 [Page 6] Internet-Draft Ad Hoc IP Addressing December 2009 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast Addresses", RFC 4193, 2005. [RFC3587] Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global Unicast Address Format", RFC 3587, 2003. [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan", RFC 4632, 2006. Appendix A. Changes since -00 This section logs the main changes of this document since its last version. These are: Facts on the needs of applications other than routing - At the end of the intro, added a disclaimer on the fact that apps other than routing may need additional addresses (potentially plus prefixes, and such, better global than local, but that the doc focuses only on what is necessary for the routing protocols to be functional. Modified list of issues pertaining to the use of LLs - Removed DAD issue as argument for why link-local addresses are not recommended for use. Other issues, that remain listed in this document, are still sufficient to reach the same conclusion. More precise expression of the model for IPv6 - Reworded the "/128 IPv6 prefixes" recommendation into "there is no on-link prefix" recommendation. More precise expression of the applicability of the model - Better expression of recommendation that "if you know something about reachability o addresses or interfaces" then you may leverage this to configure an on-link prefix in the last paragraphs of section 3 and 4. Appendix B. Contributors This document reflects discussions and contributions from several individuals including (in alphabetical order): Teco Boot, Ulrich Herberg, Thomas Narten, Erik Nordmark, Charles Perkins and Zach Shelby. Baccelli, Ed. & Townsley, Ed. Expires June 10, 2010 [Page 7] Internet-Draft Ad Hoc IP Addressing December 2009 Authors' Addresses Emmanuel Baccelli INRIA Email: Emmanuel.Baccelli@inria.fr URI: http://www.emmanuelbaccelli.org/ Mark Townsley Cisco Systems Email: townsley@cisco.com Baccelli, Ed. & Townsley, Ed. Expires June 10, 2010 [Page 8]