Internet Draft D. Thaler
February 25, 2006 Microsoft
Expires August 2006
Multi-Subnet MANETs
<draft-thaler-autoconf-multisubnet-manets-00.txt>
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of 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/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Copyright Notice
Copyright (C) The Internet Society (2006). All Rights Reserved.
Abstract
This document describes an approach to addressing nodes in Mobile
Ad-hoc Networks (MANETs) which involves assigning a separate subnet
to each MANET router. This approach avoids many of the problems
that arise in other approaches, and is intended to allow existing
protocols and applications to work unmodified.
1. Introduction
A Mobile Ad-hoc Network (MANET) is one in which the topology may be
very dynamic, such as highly mobile nodes communicating over a
wireless medium. In this document we assume that there are
forwarding nodes which participate in a MANET routing protocol.
Furthermore, we assume that there may also be non-MANET nodes
attached behind MANET forwarding nodes (e.g., via wired Ethernet).
We will use the term "MANET router" to refer to the first type of
nodes, and "client" to refer to the latter type of nodes.
Thaler Expires August 2006 1
Draft Multi-Subnet MANETs February 2006
There are three general approaches to architecting the data
(forwarding) plane:
(A) Treat the entire MANET as a single link, and do all forwarding
at the datalink-layer, exposing (say) normal Ethernet to IP.
The control plane thus consists of a layer-2 routing protocol.
In this approach, existing protocols and applications work
normally.
(B) Treat the MANET as a single subnet composed of multiple links,
such that MANET routers must do layer-3 forwarding (decrement
TTL, etc.) between nodes in the same subnet. The control plane
consists of a layer-3 MANET routing protocol. This approach
has a number of problems as discussed in [MLSI], and may break
existing protocols and applications. Clients are either not
supported at all, or some additional proxying method is
required.
(C) Treat the MANET as a site containing many subnets, such that
MANET routers act as normal routers when forwarding data
between subnets. The control plane consists of a layer-3 MANET
routing protocol, as with approach (B). This approach avoids
most of the problems of (B), easily supports clients, and is
what the remainder of this document outlines.
2. Overview
The MANET is treated as a site composed of many subnets. Each MANET
router is assigned its own subnet prefix(es). Each client is
assigned its own IP address(es) on a subnet assigned to a MANET
router to which it is attached.
The MANET site may or may not have external connectivity. If there
is, then any site gateways are configured with the site prefix(es)
and advertise them into the external routing system, as normal site
gateways do. If there is no external connectivity, then one or more
MANET routers are configured with the site prefix(es), e.g., a
Unique Local IPv6 Prefix [RFC4193], and 10/8 for IPv4 [RFC1918]. It
may be possible to automatically generate a site prefix for the site
in a zero-configuration MANET (e.g., by electing one node to do so),
but such a mechanism is outside the scope of this document. Note
that a /48 IPv6 site prefix results in the ability to support up to
2^16 MANET routers, plus any clients behind them.
Each router then uses a subnet allocation protocol to acquire one or
more subnet prefixes within the site prefix. It then uses this
subnet prefix to number itself and any clients.
As a result, this approach needs only two MANET-specific protocols:
1) A routing protocol capable of exchanging subnet routes, and
2) A subnet allocation protocol capable of allocating prefixes.
Thaler Expires August 2006 2
Draft Multi-Subnet MANETs February 2006
All other protocols and applications operate normally.
3. Client Behavior
Clients operate with no changes, using normal IPv4 and IPv6
mechanisms.
4. MANET Router Behavior
4.1. Obtaining a subnet prefix
The requirements for a subnet allocation protocol are:
1) Must be capable of allocating a subnet prefix (not just a single
address).
2) Must prevent duplicate subnet prefix assignments.
3) Must handle network partitions and heals, due to the highly
dynamic nature of a MANET.
4) Must complete rapidly, with low overhead.
5) Must support a bootstrap scenario where all MANET routers without
a manually configured prefix attempt to allocate a prefix at the
same time.
6) Should support the ability to detect duplicate layer-2 addresses.
7) Should support the ability to detect a duplicate IPv6 link-local
address within the MANET site (since the dynamic nature means
that any other router may eventually be on the same link, this
helps avoid future conflicts).
Details of the actual subnet allocation protocol are outside the
scope of this draft. At a high level, an address allocation
protocol proposed for a multilink-subnet approach (approach B) can
be modified to be suitable, by inclusion of a prefix length.
4.2. Using a subnet prefix
One common practice in BGP is to assign a routable address to the
router's loopback interface, and use that for communication which
may be routed over different physical interfaces over time (e.g., to
survive failures).
In the same vein, a MANET router takes its allocated prefix, assigns
it to its loopback interface, and advertises it in the MANET routing
protocol. If the MANET router also has a client interface (e.g., an
Ethernet link with wired clients attached), then the implementation
can either allocate a second subnet prefix for that link, or may
simply assign its sole subnet prefix to a client interface rather
than its loopback interface. The MANET router then assigns its own
Thaler Expires August 2006 3
Draft Multi-Subnet MANETs February 2006
IPv4 and/or IPv6 addresses on its loopback interface by using a
fixed address suffix (e.g., .1 in IPv4 and ::1 in IPv6).
The MANET router's other interfaces (e.g., a wireless interface used
to communicate with other MANET routers) is not given an IPv4
address (i.e., left unnumbered). An IPv6 link-local address is
assigned per normal IPv6 stateless address autoconfiguration
[RFC2462]. Note that normal IPv6 Duplicate Address Detection may
occur as usual, but the MANET routers seen on that link will change
over time. DAD need not be redone as long as the subnet allocation
protocol is responsible for detecting duplicate IPv6 link-local
addresses.
Applications running on the MANET router will use the loopback
interface, since that is the one with the global address on it. All
other MANET nodes will appear to the application as being off-
subnet.
5. Security Considerations
Often the hardest attacks to defend against are on-link attacks
(e.g., ARP attacks in IPv4). Unlike the other two approaches, this
approach narrows the set of nodes which are on-link to only those
nodes which are nearby, as opposed to being anywhere in the MANET.
In addition to mitigations in various protocols, this may make
social mitigations easier as well.
In addition, since this approach does not change the standard
address allocation and forwarding mechanisms in IPv4 and IPv6, it
avoids the security issues mentioned in [MLSI], resulting in a
potentially more secure environment than with a multilink subnet
approach.
The routing protocol in use must be secured to avoid attackers
misrouting packets. The issues here are discussed in [RFC2501].
The subnet allocation protocol in use must also be secured to avoid
attackers consuming all available subnet space, or preventing
legitimate MANET routers from obtaining a subnet prefix.
6. IANA Considerations
This document has no actions for IANA.
7. Acknowledgements
Suresh Krishnan first suggested assigning a subnet prefix to each
MANET node.
Thaler Expires August 2006 4
Draft Multi-Subnet MANETs February 2006
8. Normative References
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
and E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
9. Informative References
[MLSI] Thaler, D., "Issues With Protocols Proposing Multilink
Subnets", draft-thaler-intarea-multilink-subnet-issues-
00.txt, February 2006.
[RFC2501] Corson, S. and J. Macker, "Mobile Ad hoc Networking
(MANET): Routing Protocol Performance Issues and
Evaluation Considerations", RFC 2501, January 1999.
Authors' Addresses
Dave Thaler
Microsoft
One Microsoft Way
Redmond, WA 98052
Phone: +1 425 703 8835
Email: dthaler@microsoft.com
Thaler Expires August 2006 5
Draft Multi-Subnet MANETs February 2006
Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed
to pertain to the implementation or use of the technology described
in this document or the extent to which any license under such
rights might or might not be available; nor does it represent that
it has made any independent effort to identify any such rights.
Information on the procedures with respect to rights in RFC
documents can be found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use
of such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository
at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
Thaler Expires August 2006 6