Subject: [Fwd: Subnetwork and addressing in ad-hoc networks]

From: Bruno Husson <[email-masked]>
Date: Wed, 21 Nov 2001 12:38:23 +0100

--
Bruno HUSSON
Tel : +33 1 46 08 61 92
Fax : +33 1 46 08 61 10
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Subject: Subnetwork and addressing in ad-hoc networks
From: Bruno Husson <[email-masked]>
To: David Lundberg <[email-masked]>
Cc: Yves Pr?t <[email-masked]>, Colin Perkins <[email-masked]>
Date: Wed, 21 Nov 2001 10:44:38 +0100

Hi,

David Lundberg a écrit :

> Hi!
>
> > 8.11 Why is broadcast 255.255.255.255 ? isn't this a little general and
> > couldn't one use a less generic broadcast address mask ?
>
> Since the nodes around is not requiered to be on the same
> subnetwork.
>

It depends what you call a subnetwork.
I think that in many use cases,  nodes of an ad-hoc network can share a
common "network id". Thus broadcasting can be limited to that network id
(broadcast address composed of the network id followed by "1111...").

A node is not allowed to have any IP address of its choice when it is
connected on a given LAN.
I think an ad-hoc node should not be allowed to have any IP address. A
"network id" should be defined for each ad-hoc network (or ad-hoc
subnetwork).

The addressing problem has not been solved in ad-hoc networks.
An IPv4 address is normaly composed of a "network id" and a "host id".

In draft_ietf_manet_autoconf-00.txt, a value for the "network id" is proposed
: 169.254/16
and also a Duplicate Address Detection (DAD) mechanism for connex networks.
I agree with the DAD mechanism but disagree with a unique "network id" common
to all ad-hoc networks on the earth.

tony mcauley et al. recently presented a short paper called
"self-configuring netwhorks" at the ARL Federated Laboratory 4th Annual
Symposium which
presents a DHCP-based extension for dynamic address assignment in ad hoc
nets, in
http://search.ietf.org/internet-drafts/draft-itsumo-drcp-00.txt

Some have proposed that each node has a fixed adressed. Others propose that
address could change depending of node movements....

I personally think that addresing in ad-hoc should be compliant with other
networks, meaning that internetwork routing should also work when ad-hoc
networks are interconnected with fixed networks (internet for instance).
I think an ad-hoc network could be a subnetwork of a more important network.
An ad-hoc network could be considered as a unique network or composed of
several sub-networks, depending on the administrative organization, and on
the possible topology (totally meshed or nodes moving inside defined
separated areas...), exactly like for LANs.

Thus, the address class could be one of  B or C classes. As long as a node
stays in the same subnetwork, I think it should keep the same address. This
address is composed of the network-id corresponding to the sub-network inside
which it is (the network id is given by configuraiton of the node) and a host
id ideally calculated from its MAC address or possibly a random one at
initialization with a DAD mechanism limited to the sub-network.
This could answer to most ad-hoc addressing needs including possible
interconnection of an ad-hoc network  with fixed networks.

The limits of such a solution comes where nodes with different  network id
(i.e. members of different subnetworks) are neighbour and try to communicate
one with the other. In that case, some nodes should play the role of a
gateway between two subnetworks. So, subnetworking inside an ad-hoc network
should be restricted to specific cases where subnetworks are clearly
separated with some defined gateways between them. (this looks like the
notion of zone of some manet routing protocol like ZRP).  In that case, a
node moving from one subnet to another could possibly get a new address with
some mechanisms like address autoconfiguration and resolve routing with
mechanisms like MobileIP. DHCP and Mobile IP should be adapted in the ad-hoc
environment, as they usually imply fixed servers.

Finally there is the case of very large ad-hoc networks, with thousands of
nodes, able to move anywhere and to communicate with any other node. Is there
a clear use case (market) for this kind of problem? If yes, I am interested
to hear more about it.

--
Bruno HUSSON
Tel : +33 1 46 08 61 92
Fax : +33 1 46 08 61 10
Standard : +33 1 46 08 61 00
e-mail:[email-masked]
-----------------
SYCOMORE - Groupe EADS
Immeuble l'Etendard
63 ter, Avenue Edouard VAILLANT
92517 BOULOGNE-BILLANCOURT
http://www.sycomore.fr
------------------------------------------------------