Subject: Scaling question regarding AODV

From: Fred Baker <[email-masked]>
Date: Mon, 07 Jan 2002 08:39:00 -0800

I am relatively new to the Manet list, although I have been pretty much 
aware of the work and the issues. I am now reading through the DSR and AODV 
drafts.

One thing that doesn't make much sense to me in either one, and especially 
in AODV, is that they focus on routing to addresses, rather than to CIDR 
prefixes. I understand that sensors will often literally use isolated 
addresses as "router identifiers", but it seems that in many cases one 
would like the option of talking about a set of addresses which will move 
together - the addressable components of a vehicle, a set of PCs that live 
at a command post, and so on. Since an IPv4 address is trivially a prefix 
with a length of 32 bits, it seems odd to me to not include a prefix length 
in the routes as distributed, allowing the option of route aggregation and 
the use of LANs.

Can someone explain why this is not a feature of the protocol?

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From: "Charles E. Perkins" <[email-masked]>
Date: Mon, 07 Jan 2002 13:32:24 -0800

Hello Fred,

You wrote:

> prefixes.

A lot of ad hoc networks are going to be built from nodes other
than sensors, although I agree that sensor networks are likely
to be an important kind of ad hoc network.  AODV in particular does
allow routing to a CIDR prefix.  The reason that individual node
addresses are usually under consideration, is that this gives the
maximum amount of flexibility for movement.  A route for a CIDR
prefix might be valid only under the assumption that all the nodes
with the same prefix move together.  There have been solutions that
incorporate a sort of "home agent" reachable by way of the CIDR-prefix
route.  I'm not sure how to characterize the advantages of such a
system over one that requires all nodes with the same prefix to be
located together.

>         I understand that sensors will often literally use isolated

AODV can do this.

Regards,
Charlie P.

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From: Joe Macker <[email-masked]>
Date: Mon, 07 Jan 2002 18:51:51 -0500

Fred/All:

It has also never been clear to me why prefix advertisement mechanisms should be precluded.  While in certain cases manet nodes may be isolated single hosts with single addresses (sometimes i feel people get stuck on this particular application), protocols should be capable of supporting prefix advertisements when and where appropriate (In most cases its reasonably trivial to add the functionality).

OLSR IDv5, for one, discusses a capability to advertise associated networks and interfaces allowing one to advertise and build appropriate distributed routes for manet with attached fixed networks.  Its definitely limiting not to support such a capability when you really start going operational.  We have already been experimentally using this capability around our laboratory environment to support advertisement of fixed networks attached to an operational manet node.

-Joe

At 08:39 AM 1/7/2002 -0800, Fred Baker wrote:
>I am relatively new to the Manet list, although I have been pretty much aware of the work and the issues. I am now reading through the DSR and AODV drafts.
>
>One thing that doesn't make much sense to me in either one, and especially in AODV, is that they focus on routing to addresses, rather than to CIDR prefixes. I understand that sensors will often literally use isolated addresses as "router identifiers", but it seems that in many cases one would like the option of talking about a set of addresses which will move together - the addressable components of a vehicle, a set of PCs that live at a command post, and so on. Since an IPv4 address is trivially a prefix with a length of 32 bits, it seems odd to me to not include a prefix length in the routes as distributed, allowing the option of route aggregation and the use of LANs.
>

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From: "Jim Fleming" <[email-masked]>
Date: Mon, 7 Jan 2002 18:30:43 -0800

----- Original Message -----
From: "Fred Baker" <[email-masked]>
> with a length of 32 bits, it seems odd to me to not include a prefix
length

Trivial extensions to IPv4 and the recognition of UDP and TCP as the
workhorse services, extends the 32 bits with....
QoS +4
RIFRAF +4
Port +16
....these 24 additional bits come to light when DNS AAAA records are used
with IPv4.

http://www.dot-biz.com/INFO/Papers/

Jim Fleming
2002:[IPv4]:000X:03DB
http://www.IPv8.info

---

From: Fred Baker <[email-masked]>
Date: Mon, 07 Jan 2002 16:33:22 -0800

OK, I found the word "prefix" in the draft. I was waiting for draft 10 to 
read it thoroughly, so I missed that. The question came up first in DSR 
(which I just finished reading), which mentions prefixes without definition 
and only once.