how to forward packets on two NICs

Hi all

I have to build a sniffer on our voip network so as to monitor what is going
wrong on it (bad communications quality) and my problem is that I can't
mirror the traffic because the switchs are not manageable. All the IP phones
are on the same subnet and the IPBX is the gateway.
Because I am not familiar with Voip protocols, I don't know really how all
this stuff is working... And I am looking for a solution which won't need to
change the IP topology... if it's possible.


I had the idea to configure the sniffer with two NIC and to forward all the
packets from one NIC to the other one, like a switch with 2 ports if you
want (I know that this is not a very good way to act but has I have said, I
would like to avoid changing the IP of the IPBX).

Do you think it is a solution ? If yes, do you know how to configure that ?
if no, do you see another solution ?

I have found a package call parprouted which allows to forward the ARP
requests, now I guess that I just have to find the same thing for IP packets
as there is no dhcp/bootp protocols here...


thanks in advance

On Mon, 03 Nov 2008 16:03:26 +0100, Julien Simbola wrote:

> I had the idea to configure the sniffer with two NIC and to forward all
> the packets from one NIC to the other one, like a switch with 2 ports if
> you want (I know that this is not a very good way to act but has I have
> said, I would like to avoid changing the IP of the IPBX).

This is called a bridge...

Google for linux bridge howto..!


--
Regards/mvh Joachim Mæland

If everything seems under control, you're just not going fast enough.
-Mario Andretti

I have been able to set this up, thanks to you Joachim

For those who are interested in a solution, it's pretty simple
Here is the way to proceed (using 2.6 kernel):

apt-get install ebtables
apt-get install bridge-utils

brctl addr br0
brctl addif br0 eth0
brctl addif br0 eth1

ifconfig br0 up


thank you
cheers





"Joachim Mæland" <jm-(E-Mail Removed)> wrote in message
news:hqh3u5-(E-Mail Removed)...
> On Mon, 03 Nov 2008 16:03:26 +0100, Julien Simbola wrote:
>
>> I had the idea to configure the sniffer with two NIC and to forward all
>> the packets from one NIC to the other one, like a switch with 2 ports if
>> you want (I know that this is not a very good way to act but has I have
>> said, I would like to avoid changing the IP of the IPBX).
>
> This is called a bridge...
>
> Google for linux bridge howto..!
>
>
> --
> Regards/mvh Joachim Mæland
>
> If everything seems under control, you're just not going fast enough.
> -Mario Andretti
>

Hello,

Julien Simbola a écrit :
>
> Here is the way to proceed (using 2.6 kernel):
>
> apt-get install ebtables
> apt-get install bridge-utils

Ebtables is not required to set up a simple bridge. It is required only
to do layer 2 filtering/mangling on the bridge. Bridge-utils works with
a 2.4 kernel too.