Linux and VLAN

Hi

in a pen test of a Ip Voice network I have the following issue :
the ip phone sends 802.1q tagged datas to the switch and the switch
sends back non tagged datas.

I tried to simulate an IP phone Vlan behaviour to do my pen test (like
arp spoofing, dhcp corruption) but it clearly fail as if I use Vconfig
it creates a tagged interface and coming back datas are not seen by this
interface.

Is there a way to do an interface that sends taggued data and accept non
802.1q taggued data ?

regards

Sylvain Eche wrote:

> Is there a way to do an interface that sends taggued data and accept non
> 802.1q taggued data

You want to mix tagged and untagged data on the same NIC? If I remember
correctly, the eth0 interface (or ethN) would be untagged while eth0.1 (or
ethN.M) will be tagged/expect to be tagged for VLAN M.

Also remember that you can mix tagged interfaces and virtual interfaces (ie.
ethN.M:X).

- Andrew

If I remember
correctly, the eth0 interface (or ethN) would be untagged while eth0.1 (or
ethN.M) will be tagged/expect to be tagged for VLAN M.

You 're right but the problem is if I do a ping -I eth0.1
the icmp packets comes out tagged and in my case they comes back
untagged so through eth0 and my ping don't see the answer as it sticks
to eth0.1

> Also remember that you can mix tagged interfaces and virtual interfaces (ie.
> ethN.M:X).

I'm not sure to understand what you mean ?

Sylvain Eche wrote:

> You 're right but the problem is if I do a ping -I eth0.1
> the icmp packets comes out tagged and in my case they comes back
> untagged so through eth0 and my ping don't see the answer as it sticks
> to eth0.1

This sounds like a problem not with the machine sending the ICMP Ping
packets but with the machine sending the ICMP Pong packets (or perhaps a
intervening switch if the Pong-er isn't 802.1q-aware itself).

I don't experience this problem on my Linux machines that are 802.1q-aware.

If you're forced to use -I, then I wonder if it might be a routing issue.
Perhaps the Ponger has some reason to route response packets differently
than you're expecting such that they reach eth0 instead of eth0.1.

- Andrew