Autoconf Working Group C. Jelger
Internet-Draft Fraunhofer FOKUS
Expires: October 14, 2006 April 12, 2006
MANET Local IPv6 Addresses
draft-jelger-autoconf-mla-00.txt
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Abstract
This document defines how Unique Local IPv6 Unicast Addresses (RFC-
4193) can be used in wireless mobile ad hoc networks (MANETs) as
MANET Local IPv6 Addresses (MLAs). MLAs are intended to be used
inside a MANET and are not expected to be routable on the global
Internet. Each MANET node is expected to generate its MLA locally
without any coordination with other MANET nodes.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 3
3. MANET Local IPv6 Addresses (MLAs) . . . . . . . . . . . . . . . 3
3.1. Format . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Address generation . . . . . . . . . . . . . . . . . . . . 4
3.3. Address scope . . . . . . . . . . . . . . . . . . . . . . . 4
4. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 7
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1. Introduction
This document defines a possible use of Unique Local IPv6 Unicast
Addresses (ULAs)[1] as MANET Local IPv6 Addresses (MLAs) in wireless
mobile ad hoc networks (MANETs). MLAs are intended to be used inside
a MANET and are not expected to be routable on the global Internet.
Each MANET node is expected to generate its MLA locally, i.e. without
any coordination with other MANET nodes.
This extends the usage of ULAs to an extreme case where each MANET
node is considered as being a site and subnet [1] by itself. Since
MANET routing is flat (i.e. it creates /128 host routes), MANET nodes
do not necessarily need to share a network prefix for intra-MANET
communications. This loose addressing model allows to use a large
fraction of the upper 64-bit part of IPv6 addresses in order to
create addresses that are sufficiently random to avoid the use of
duplicate address detection schemes for intra-MANET communications.
2. Acknowledgements
The idea of using Unique Local IPv6 Addresses as MANET Local
Addresses has been originally discussed with a number of people
including Ryuji Wakikawa, Francisco Ros, Robert Hinden, Brian
Haberman and Guillaume Chelius. Therefore the author of this
document does not claim exclusive credit. Also note that the
formatting of this document is mostly inspired by [1].
3. MANET Local IPv6 Addresses (MLAs)
3.1. Format
Strictly speaking, MLAs have the same format as ULAs. The only
difference with ULAs is that both the Global ID and Subnet ID fields
are randomly generated. This results in a merged 56-bit field called
the Random ID.
| 7 bits |1| 56 bits | 64 bits |
+--------+-+------------------------+----------------------------+
| Prefix |L| Random ID | Interface ID |
+--------+-+------------------------+----------------------------+
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Where:
Prefix FC00::/7 prefix to identify Local IPv6 unicast
addresses.
L Set to 1. See [1] for details.
Random ID 56-bit random identifier used to create a
globally unique address.
Interface ID 64-bit Interface ID as defined in [2].
3.2. Address generation
To create an MLA for a given physical interface, a MANET node locally
generates its Random ID in a random manner. Since MANET routing is
flat and creates /128 host routes, MANET nodes do not need to share a
network prefix. Hence the Random ID is used in addition to the
Interface ID in order to create unique addresses (with a very high
probability of uniqueness). Using 56 bits gives around 7.2e+16
possible values for the Random ID, hence drastically reducing the
probability of an address collision if two nodes having the same
Interface ID generate the same Random ID.
The probability of an address collision is further reduced by the use
of EUI-64 identifiers as Interface IDs. EUI-64 that derive from
EUI-48 (e.g. IEEE 802 48-bit MAC addresses) are indeed expected to
be globally unique, while randomly generated identifiers [3] have an
extremely low collision probability (around 1.8e+19 possible values).
Given the network size currently being considered within the MANET
community (a few hundred nodes), and given the extremely large
randomness of MLAs, a node must not necessarily check whether a
generated MLA is unique. The overhead of performing duplicate
address detection (DAD) greatly superseeds its gain since the
probability of address collisions is extremely low.
Nevertheless, a passive DAD technique could be used in order to
detect address collisions, eventhough such events are very unlikely
to occur. This extra mechanism is however out of the scope of this
document.
3.3. Address scope
As Unique Local IPv6 Unicast Addresses, MANET Local Addresses have a
global scope. However MLAs are not globally routeable, and their use
is restricted inside a MANET. Since there does not exist any
standardized definition of the boundaries of a MANET, we assume that
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the use of MLAs is restricted to the set of MANET nodes (or routing
instances) willing to route packets using MLAs. This assumes that a
MANET routing protocol should always be willing to route packets
whose source and/or destination addresses are MLAs.
4. References
[1] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[2] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)
Addressing Architecture", RFC 3513, April 2003.
[3] Narten, T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001.
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Author's Address
Christophe Jelger
Fraunhofer Institute FOKUS
Kaiserin-Augusta-Allee 31
Berlin 10589
Germany
Phone: +49 30 3463 7137
Email: cje@fokus.fraunhofer.de
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