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IETF AUTOCONF Shubhranshu Singh
Internet-Draft JaeHoon Kim
Expires:April 07, 2006 SAMSUNG AIT
Charles E. Perkins
Nokia Research Center
Pedro M. Ruiz
University of Murcia
Thomas Clausen
Ecole polytechnique
October 06, 2005
Ad hoc network autoconfiguration: terminology and problem statement
draft-singh-autoconf-adp-01
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Copyright (C) The Internet Society (2005).
Abstract
A Mobile Ad Hoc NETwork (MANET) is formed by the association of
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mobile devices, usually wireless and capable of multi-hop
communication among themselves even if there is no networking
infrastructure available. The autonomous nature of these networks
requires the existence of an autoconfiguration mechanism. This
document explains terminologies, problem statement and solution
requirements for ad hoc network autoconfiguration.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Problem statement . . . . . . . . . . . . . . . . . . . . . . 7
4.1 Stand-alone ad hoc network . . . . . . . . . . . . . . . . 7
4.2 Ad hoc network at the edge of infra-structure network . . 8
4.3 Temporarily hybrid ad hoc network . . . . . . . . . . . . 8
4.4 Dealing with network mergers and partitions . . . . . . . . 9
5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
A. Normative References . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . 14
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1. Introduction
A Mobile Ad Hoc NETwork (MANET) is formed by the association of
mobile devices, usually wireless and capable of multi-hop
communication among themselves even if there is no networking
infrastructure available. However, it is generally expected that, if
some MANET nodes are connected to external networks (e.g. Internet)
some of them might act as gateways towards those networks.
There are a number of solutions on interconnecting ad hoc networks to
the Internet[4][5][7]. Most of the solutions are tightly related to
the issue of discovering Internet gateways and auto-configuring
global addresses that are routable within the Internet. Usually,
autoconfiguration of addresses in MANET is also required even when
the MANET is isolated from external networks.
Currently there is no standard definition for commonly used ad hoc
network autoconfiguration related terminologies such as standalone
MANET, MANET local addresses, etc. This document provides definition
of such terminologies, in addition to problem statement and solution
requirements for address autoconfiguration in MANET.
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2. Terminology
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [5].
Mobile Ad hoc Network (MANET) Mobile Ad hoc Network (MANET) - A
network formed by a set of mobile devices equipped with one or
more wireless interfaces. Nodes are characterized by random
mobility and run ad hoc routing protocols for multi-hop
communication.
MANET Node - A device with one or more wireless interfaces and
associated IPv address(es) which is used by the MANET routing
protocol in use.
MANET local address - An IP address configured on a MANET node,
which is valid for communication among manet nodes that are part
of the same ad hoc network. Nodes MUST NOT communicate with other
nodes outside the MANET using this address.
Global address - An IPv4 or IPv6 address configured on a MANET node,
which is valid for communication with the nodes located in the
Internet. These addresses can also be used for communication with
nodes within the MANET.
Internet gateway - A node connected to ad hoc network as well as to
the Internet and capable of providing global addressing and
bidirectional connectivity to MANET nodes. Internet gateways
should provide topologically correct IPv6 prefixes. This process
can be done in a reactive, proactive or hybrid manner. Internet
gateway mostly runs ad hoc routing protocols as well as
infrastructure network protocols such as OSPF.
Duplicate Address Detection (DAD) - The process by which a node
confirms the uniqueness of an address it wishes to configure or
has already configured. A node already equipped with an IP
address participates in DAD in order to protect its IP address
from being used by another node.
Standalone ad hoc network - A network consisting of a group of MANET
nodes capable of spontaneously creating a multi-hop ad hoc network
without any connection (either direct of via gateways) to other IP
networks such as the Internet.
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Hybrid ad hoc network - A network formed by a group of MANET nodes,
capable of spontaneously forming a multi-hop ad hoc network, in
which one or more of the nodes act as Internet Gateways providing
access to other IP networks. They can be envisioned as a
standalone MANET with one or more Internet Gateways taking part
both in the MANET and in the external network.
Network merger - The process by which two or more ad hoc networks
(either standalone or hybrid), previously disjoint, get connected.
In general, this proccess happens as a consequence of the mobility
of the nodes.
Network partitioning - The process by which an ad hoc network
(either standalone or hybrid) which was previously connected,
splits into two or more disconnected ad hoc networks. In general,
this proccess happens as a consequence of the mobility of the
nodes. When this happens, some of the routes in MANET nodes
become invalid hence some nodes may become unreachable.
Network merger detection - The process by which ad hoc nodes detect
the merger of two or more initially isolated MANETs.
Network partition detection - The process by which ad hoc nodes
detect the partition of a single MANET into two or more networks.
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3. Assumptions
o Routes between nodes in the ad hoc network MUST NOT leak into the
Internet.
o Network routes (those valid for an entire network prefix instead
of just a single node) require reachability to every node which
exists within the prefix, just as within the Internet.
o A gateway can be treated as a default router for the Internet.
o A gateway SHOULD maintain active routes for all nodes within the
MANET which are actively engaged in communications with their
partners in the Internet.
o Nodes within the Internet cannot distinguish whether or not a
gateway offers connectivity to an ad hoc network or some other
sort of stub network.
o If two gateways advertise connectivity to the same routing prefix,
then those two gateways MUST coordinate their routing tables so
that they exhibit equal reachability for all nodes within that
routing prefix.
o Multiple gateways may offer several different routing prefixes. A
node may choose which gateway's routing prefix to use for
autoconfiguration according to any convenient criterion; the
methods for making the determination are not constrained to be
only those specified within a MANET autoconfiguration protocol
specification.
o Autoconfigured addresses are likely to have lifetimes associated
with them, and after the lifetime expires use of the address
should be immediately discontinued.
o When duplicate addresses are detected, the node which has had the
address for the least amount of time MUST discontinue.
Alternatively, BOTH nodes MUST discontinue using this address.
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4. Problem statement
There are Specifications for address autoconfiguration in the
traditional IPv6 networks e.g. RFC 2462,RFC 2461, etc. However,
due to the challenges presented by MANET (as defined and understood
by the IETF MANET WG), these specifications need to be extended
for MANET environment. Unlike in the traditional IP networks, each
ad hoc node, besides being traffic end-point, should be capable of
forwarding traffic destined for other hosts i.e each ad hoc node
normally acts as a "router" as well as a "host". Additionally, the notion
of all nodes being able to access a shared communication medium fails
in MANET: since all nodes in a MANET do not share the same physical
link. A single transmission does not suffice for a broadcast or
link-local multicast to reach all nodes. Transmissions which are
otherwise not supposed to be forwarded by routers, such as limited
broadcast and link-local multicast, should be forwarded by the nodes
in order to reach all the MANET nodes. In other words, nodes constituting
an ad-hoc network do not share access to a single multicast-capable
link for signaling. Many protocol specifications used in the traditional
IP networks e.g. RFCs 2462, 2461 etc. do, however, assume that
subnet-local signals (e.g. link-local multicast signal) are received by
each of the hosts on the particular subnet without being forwarded by
the routers defining the subnet boundary.
There is a growing requirement for address autoconfiguration
solutions in the MANET environment - to be used by the ad hoc nodes
constituting standalone networks as well as edge networks. However,
the solutions should be designed with a minimal modification and
should be compliant with the specifications that are widely used in
the traditional IP networks.
Ad hoc networks can either be deployed as an standalone MANET or as
an edge network, attached to the Internet. Indeed, IETF MANET WG has
this point of view for developing the MANET routing protocols.
The autoconfiguration protocol has to carefully distinguish between
cases when a gateway offers a routing prefix, from the case when a
"local" prefix has to be used since no routing prefix is available
for the purpose. In this way, a single addressing solution is
obtained, but just as within the Internet there are different kinds
of addresses. Some parallels can be drawn between the "manet local"
addressing and the "zeroconf" solution devised within the IETF
working group of the same name. However, there may be differences
which are discovered as more development occurs towards the
specification of the address autoconfiguration protocol.
4.1 Stand-alone ad hoc network
Examples of standalone ad hoc networks are conference-room networks,
battlefield networks, surveillance networKs, etc. For these
networks, IPv4 and/or IPv6 address auto-configuration mechanism is
needed.
These addresses should be routable only within the particular ad hoc
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network and should be unique even in situations where two or more
networks, initially isolated, merge together to form a single
network. Network merger can occur anytime and makes the address
uniqueness maintenance quite challenging in such situations.
4.2 Ad hoc network at the edge of infra-structure network
Fig.1. shows an ad hoc network deployed at the edge of the Internet.
H1
|
+---------------+
| Internet |
+---------------+
* *
* *
GW1* *
| GW2
| |
---N1 |
/ | |
N4 | N2--- N5
| |
N3-----------+
Fig. 1: Hybrid ad hoc network connected to Internet.
Hybrid networks can be envisioned as an standalone network connected
to the Internet via one or more Internet Gateways. These gateways
are located between the two networks and are capable of providing
globally routable addresses as well as bi-directional connectivity to
the ad hoc nodes connected to it either directly (1-hop) or via one
or more intermediate nodes. These gateways may either be fixed or
mobile, single or multiple, equipped with wired and/or wireless
interfaces.
Ad hoc nodes may use Internet gateway for global prefix allocation
and configuration of globally routable addresses. However, it
introduces issues such as how MANET nodes receive and/or Internet
gateway provides globally routable prefixes, etc. Hence, for such
network sufficient but limited detail about Internet gateway
discovery and operation is required, along with an address
autoconfiguration solution.
4.3 Temporarily hybrid ad hoc network
Temporarily hybrid ad hoc network scenario arise due to the situation
where an ad hoc network may be sometimes stand-alone and sometimes
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connected to the Internet e.g. a car or subway network connected
while parked or at station and disconnected otherwise.
Basically, the problems in this case are similar to those introduced
in the above two cases. However, in this case, ad hoc nodes should
detect the lack of reachability to the Internet and SHOULD maintain
their allocated addresses for the lifetime which has been assigned
during the autoconfiguration process. For local addresses, no such
lifetime is necessary, but could anyway be assigned as a minimal
protection against partitioning.
4.4 Dealing with network merges and partitions
By the nature of MANET, two or more ad hoc networks which are
initially isolated, can merge together or a single ad hoc network can
get partitioned into two or more separate networks, at any moment in
time. While network partitioning may not cause any severe problem in
the MANET's operation, it may be needed that network partitioning is
detected so that the resources (e.g. limited number of addressed) can
be re-used among the nodes. Network merger introduces challenges to
maintain the address uniqueness. Normally, once an address is
allocated to a node, it continues using it and at the same time
defending its own addresses from being allocated to any other node.
However, since initially isolated ad hoc networks allocates
addresses independent with each other, there remains some probability
of more than one node using same address once two/more independent
ad hoc networks merge.
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5. Requirements
In order to offer a lightweight but interoperable auto-configuration
mechanism a number of requirements SHOULD be satisfied. These
requirements include:
Extensibility - The mechanism SHOULD be able to accomodate future
extensions and optimizations.
Efficiency - Given that network resources tend to be scarce in
MANETs, autoconfiguration mechanisms SHOULD be lightweight in
nature, and avoid making an excessive use of the network
resources.
Independence from ad hoc routing protocols - Autoconfiguration
mechanisms SHOULD be able to operate with different proactive and
reactive routing protocols.
Interoperable with fixed IP networks - When there are one or more
Internet gateways within a MANET, the address autoconfiguration
approach should provide global addresses to MANET nodes in such a
way that they MUST be able to interoperate with any IP host in the
Internet, using standard protocols.
Resilience and robustness - Given the dynamic nature of MANETs,
autoconfiguration mechanisms SHOULD be resilient and roubust to
packet losses, network partitions, network merges as well as
disconnections from fixed IP networks or Internet Gateways.
Validity both for IPv4 and IPv6 - Autoconfiguration mechanisms
SHOULD be capable of working both for IPV4 and IPv6
autoconfiguration.
Scalable - MANET autoconfiguration protocols should avoid increasing
congestion in the MANET as the number of MANET nodes increases, or
as they travel at higher speeds, or as more communication partners
launch applications within the ad hoc network, or as the frequency
of network partitions increases.
Simplicity - Autoconfiguration mechanisms should be easy to test and
deploy.
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6. Security Considerations
Since this document does not specify any protocol, no additional
security vulnerabilities are created. However, experience with other
address autoconfiguration protocols indicates that it is difficult to
expect a very high degree of security. This is especially true in an
ad hoc network using manet-local addresses, since it may be
unfeasible to interact with any pre-existing security infrastructure.
Nevertheless, the protocols should be designed to avoid as many
security pitfalls as can be avoided. This may involve using
collaboration histories and out-of-band mechanisms requiring user
interventions.
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Appendix A. Normative References
o [1] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
o [2] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
o [3] Engelstad, P., Tonnesen, A., Hafslund, A. and G. Egeland,
"Internet Connectivity for Multi-Homed Proactive Ad Hoc Networks",
First IEEE International Conference on Sensor and Ad hoc
Communications and Networks, October 2004.
o [4] Ryuji Wakikawa et. al. Global connectivity for IPv6 Mobile Ad
Hoc Networks, IETF "draft-wakikawa-manet-globalv6-03.txt"
o [5] Shubhranshu Singh, Kim, JH., Choi, YG., Kang, KL. and YS.
Roh, "Mobile multi-gateway support for IPv6 mobile ad hoc
networks" I-D draft-singh-manet-mmg-00.txt, June 2004.
o [6] Perkins, C., Malinen, J., Wakikawa, R. and E. Belding-Royer,
"IP Address Autoconfiguration for Ad Hoc Networks", I-D
draft-perkins-manet-autoconf-01.txt, November 2001.
o [7] Cha, H., Park, J. and H. Kim, "Extended Support for Global
Connectivity for IPv6 Mobile Ad Hoc Networks", October 2003.
o [8] Jeong, J., Park, J., Kim, H. and D. Kim, "Ad Hoc IP Address
Autoconfiguration", I-D draft-jeong-adhoc-ip-addr-autoconf-02.txt,
February 2004.
o [9] Paakkonen, P., Rantonen, M. and J. Latvakoski, "IPv6
addressing in a heterogeneous MANET-network", I-D
draft-paakkonen-addressing-htr-manet-00.txt, December 2003.
o [10] Jelger, C., Noel, T. and A. Frey, "Gateway and address
autoconfiguration for IPv6 adhoc networks", I-D
draft-jelger-manet-gateway-autoconf-v6-02.txt, April 2004.
o [11] Sun, Y. and E. Belding-Royer, "A study of dynamic addressing
techniques in mobile ad hod networks", I-D Wireless communication
and mobile computing, May 2004.
o [12] Engelstad, P., Tonnesen, A., Hafslund, A. and G. Egeland,
"Internet Connectivity for Multi-Homed Proactive Ad Hoc Networks",
First IEEE International Conference on Sensor and Ad hoc
Communications and Networks, October 2004.
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Authors' Addresses
Shubhranshu
Samsung AIT, Comm & Network Lab
Phone: +82 31 280 9569
Email: Shubhranshu@gmail.com
JaeHoon Kim
Samsung AIT
Comm & Network Lab
Phone: +82 31 280 9532
Email: jaehoonk@samsung.com
Charles E. Perkins
Nokia Research Center,
Communications Systems Laboratory
Phone: +1 650 625 2986
Email: charliep@iprg.nokia.com
Pedro M. Ruiz
University of Murcia
Dept. Information and Communications Eng.
Facultad de Informatica
Campus de Espinardo s/n,
Spain
Phone: +34 968367646
Email: pedrom@dif.um.es
Thomas Heide Clausen
LIX, Ecole Polytechnique
Phone: +33 6 6058 9349
Email: T.Clausen@computer.org
URI: http://www.lix.polytechnique.fr/Labo/Thomas.Clausen/
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