Autoconf E. Baccelli, Ed.
Internet-Draft INRIA
Intended status: Informational M. Townsley, Ed.
Expires: March 28, 2010 Cisco Systems
September 24, 2009
IP Addressing Model in Ad Hoc Networks
draft-baccelli-autoconf-adhoc-addr-model-02
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 March 28, 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 in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Abstract
This document describes a model for configuring IP addresses and
subnet prefixes on the interfaces of routers which connect to links
Baccelli, Ed. & Townsley, Ed. Expires March 28, 2010 [Page 1]
Internet-Draft Ad Hoc IP Addressing September 2009
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 . . . . . . . . . . . . . . . . . . . . . . . . 4
6.2. IPv6 Model . . . . . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
9. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Appendix A. Open Issues . . . . . . . . . . . . . . . . . . . . . 6
Appendix B. Contributors . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
Baccelli, Ed. & Townsley, Ed. Expires March 28, 2010 [Page 2]
Internet-Draft Ad Hoc IP Addressing September 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 rather stable, design of the network
topology and associated IP interface configuration is rather
straightforward. As link-level assumptions become less-known and
more unstable, the design of network-level topology becomes
increasingly difficult. When assumptions about link-level
connectivity are fully absent, there is no canonical method for
determining a given IP interface configuration. This document
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 interface. It specifies addresses and subnet prefixes to be
configured on network interfaces.
When more specific assumptions can be made regarding the connectivity
to other interfaces on the link, 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 IPv6 link-local addresses are assumed to be "on
Baccelli, Ed. & Townsley, Ed. Expires March 28, 2010 [Page 3]
Internet-Draft Ad Hoc IP Addressing September 2009
link", the utility of IPv6 link-local addresses is limited as
specified in Section 6.2.
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 translates in the
following policy: no two such interfaces in the network should be
configured with the same subnet prefix.
As communication is allowed between interfaces of different routers
on a link even if these interfaces are configured to appear within
different subnets, IP packet exchange between routers on that link is
still enabled.
If on the contrary, assumptions can be made regarding connectivity to
other interfaces on the link, 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 the routing domain at least.
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
translates in the following policy: 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 a practical translation for these principles,
respectively for IPv4 and IPv6.
6.1. IPv4 Model
For IPv4, the principles described in Section 4 and Section 5 suggest
the following rules:
Baccelli, Ed. & Townsley, Ed. Expires March 28, 2010 [Page 4]
Internet-Draft Ad Hoc IP Addressing September 2009
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
/32.
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 neighbors
may be constantly moving in and out of reachability. 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 and DAD would not detect
that.
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.
Therefore MANET autoconfiguration solutions will primarily focus on
configuring IP addresses that are not IPv6 link-local.
7. IANA Considerations
This document has no actions for IANA.
Baccelli, Ed. & Townsley, Ed. Expires March 28, 2010 [Page 5]
Internet-Draft Ad Hoc IP Addressing September 2009
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.
[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.
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
Baccelli, Ed. & Townsley, Ed. Expires March 28, 2010 [Page 6]
Internet-Draft Ad Hoc IP Addressing September 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 March 28, 2010 [Page 7]