Subject: Difficulty implementing a gateway node for a peer-to-peer ad hoc network using AODV routing

From: [email-masked]
Date: Wed, 13 Feb 2002 15:06:46 -0800

Hi all,

I am trying to connect a network of ad hoc nodes (running in peer-to-peer
mode using AODV routing) to our company intranet using a 'gateway node'.
This 'gateway node' contains 2 network interfaces :
- 1 wireless (802.11) for speaking to the ad hoc nodes (hereafter referred
to as GN-eth-802.11), and
- 1 wired (802.3 i.e. regular ethernet) for speaking to the company
intranet (hereafter referred to as GN-eth-802.3).

Below is a rough ASCII sketch of the arrangement :

                                                                 'gateway
node'
     -----------       802.11
----------------------------------------------------          802.3
--------------------------------
     | Client |    <---------->   |  GN-eth-802.11   |   GN -eth-802.3   |
<---------->   |  Company Intranet   |
     -----------
----------------------------------------------------
--------------------------------

After booting the gateway node and a client node (but before enabling the
AODV routing), I can ping from the client node to all of the following
successfully i.e.

Client   --------------------->  GN-eth-802.11
(successful)
Client   ------------------------------------------------->  GN-eth-802.3
(successful)
Client
----------------------------------------------------------------------------------------------->

Company intranet    (successful)

However, after starting up AODV, the client node can still reach the
wireless interface of the gateway node (GN-eth-802.11), but can no longer
reach the wired interface of the gateway node (GN-eth-802.3) or the company
intranet i.e.

Client   --------------------->  GN-eth-802.11
(successful)
Client   -------------------------------------XXX--------->  GN-eth-802.3
(NOTsuccessful)
Client
-------------------------------------XXX---------------------------------------------------->

Company intranet    (NOT successful)

It seems that as soon as I 'insmod' the AODV routing module, it breaks the
connection to the wired segment fo the network.  I looked at the kernel IP
routing table (using the 'route' command) and can see that the AODV module
has updated the kernel IP routing table (which is to be expected for the
wireless 802.11 ethX interface).  However, after 'insmod'ing the AODV
routing module, some of the routing entries for the wired 802.3 ethX
interface also seem to have been modified / deleted.  I have tried looking
at the differences and manually adding some of the desired route entries
using the 'route add' command, but have so far been unsuccessful in
reconnecting the wired part of the network once AODV is running.

So finally ;-) , my questions are :

- has anyone successfully configured a 'gateway node' with both wired and
wireless network interfaces, and where AODV routing is used for the ad hoc
nodes running in peer-to peer mode ?

- is this a configuration issue, or does installing the AODV module change
something else in addition to modifying the kernel IP routing table ?

- is there another (better or easier) way of implementing a gateway node
for connecting a wired network to a wireless network running AODV,
OPERATING IN PEER-TO-PEER MODE (since the ad hoc nodes are running in
peer-to-peer mode, I can't just use a COTS wireless router operating in
infrastructure mode) ?

Any advice / information much appreciated.

Thanks.

- Piers.

---

From: JMG <[email-masked]>
Date: Thu, 14 Feb 2002 10:58:21 +0100

Hello,
It seems that the problem is how to inject a defaut route for ad hoc nodes to reach a fixed network.
Is this question has already  been discussed in the working group ?
In Piers's case, is there a way to configure AODV on the gateway node to advertise "I'm the default
gateway" ?
Is it specific to on-demand routing protocols or is it the same for proactive protocols like OLSR ?

thanks
Jean-Mickaël

---

From: Erik Nordström <[email-masked]>
Date: 14 Feb 2002 11:21:13 +0100

Hello Piers.

AODV currently does not define a way to do "Internet gatewaying". The
main problem has to do with the way subnets should be handled in an
ad-hoc network. The AODV draft says that nodes should be able to have IP
addresses belonging to different subnets, but they should still be able
to communicate directly. This clearly breaks the subnet idea of
"traditional" IP routing and makes Internet gatewaying impossible.
Apparently, the way to do this is a MANET problem, something not decided
on yet. However, there exists a few drafts on how to connect an ad-hoc
network to the Internet.

I don't know which implementation of AODV you are using, but it sounds
like "kernel-aodv". I don't think that implementation has any Internet
gateway support.

If you want to experiment, you could try the AODV-UU implementation
(version 0.2) which has experimental Internet gateway support. This
feature is implemented with the restriction that nodes should be
configured with IP-addresses on the same subnet.

http://www.docs.uu.se/~henrikl/aodv/

Otherwise I would recommend using LUNAR, which is a bit more robust, but
are created for smaller networks of up to around 10 nodes.

http://www.docs.uu.se/docs/research/projects/selnet/lunar/

I hope this answers your questions.

/Erik Nordström, 

Uppsala University.