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
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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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