Re: 2 NIC's on same network, possible?

[Ansgar Wiechers <bugtraq () planetcobalt net>]

On 2003-07-27 Vineet Mehta wrote:
> My collegue has a Linux machine which has 2 NIC's on it. What he did
> was assign the IP's 192.168.0.6/24 and 192.168.0.7/24 to the NIC's.
> And he was trying to ping the network but was getting errors (i dont
> know the errors).
>
>                -----------------
>               | Switch          |
>               |_________________|
>                 |             |
>                 |             |
>                 |             |
>           -------------------------------
>           |  NIC1            NIC2       |
>           |192.168.0.6/24 192.168.0.7/24|
>           |        Machine              |
>           |-----------------------------|
>
> I tried explaining him like this:-> 
>
> Configuring the machine's network like this is not a big problem, coz
> other machines on the network can still see these 2 IP's. But his
> machine will not be able to reach other machines on the network coz 2
> NIC's point to the same network so Linux kernel would be confused for
> which NIC to use to send packets.

Correct. Your machine can't have two routes pointing towards the same
network.

> If by any means we set the route to use ANY one NIC to reach the
> network then there will be no errors.

Probably (not sure about that). But you will at least double the traffic
your machine causes (provided it works at all).

> Am i right in this, or this is not possible AT ALL? I took my thought
> from the concept of IP Aliasing.

Why would he want to connect two Interfaces to the same network? The
only reason I can think of is port-trunking, but in that case the
operating system would handle both interfaces as one (AFAIK).

Regards
Ansgar Wiechers

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