[LARTC] linux bridging problem: how to emulate 2 separate interfaces on a single one?

[Antonio Pinizzotto]

Hi all.

I would need to use a single physical interface on a Linux box to manage 
two different IP addresses (belonging to two separate logical subnets) 
with two different MAC address. (I need to emulate te presence of two 
separate physical interfaceses for a PC on the same LAN, at layer 2 and 
layer 3).

Is it possible to use the linux ethernet bridging code and two tap 
interfaces for this purpose?


Here is a picture of what I need to do.


  LAN__________________________________
                     |
                     | eth0 (no IP)
             ________|________
            |                 |
            |       br0       |
            |     (no IP)     |
            |_________________|
           tap0  |        | tap1
192.168.40.1/24 |        | 192.168.30.1/24
           MAC_0 |        | MAC_1
               __|________|__
              |              |
              |      PC      |
              |              |
              |______________|


I would need this picture to be equivalent to this one:


  LAN__________________________________
           eth0  |        | eth1
192.168.40.1/24 |        | 192.168.30.1/24
           MAC_0 |        | MAC_1
               __|________|__
              |              |
              |      PC      |
              |              |
              |______________|


I tried but it doens't work. I don't know if it's not contemplate or if 
I did a wrong configuration.
For example, on tap0, using tcpdump, I see all the L2 broadcast frames 
going on the LAN; but on the counters of "ifconfig tap0" all of them are 
considered dropped. No packet is counted as transmitted or received, 
also if I try to ping from or to tap0.
The tap interface starts to transmit/receive pachets only if it is 
connected to some process like qemu or openvpn.
Maybe, it is not possibile for tap interface to be used directly by the 
linux os?


Thanks!

Antonio