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

[Stephen Hemminger]

On Fri, 01 Jul 2005 11:59:08 +0200
Antonio Pinizzotto <antonio.pinizzotto at iit.cnr.it> wrote:

> 
> 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?
>


Stop abusing bridging.  People keep trying these wacky multiple
network things and they won't work. Bridging really can't handle anything
with multiple interfaces that could possibly create a forwarding loop.