[Bridge] Re: Adding same physical port to multiple bridges

Josh Lehan bridge at krellan.com
Wed Jan 28 17:38:26 PST 2004

Stephen Hemminger wrote:

> Probably not. What are you trying to do?  Might to be bridge the
> physical LAN and do any filtering based on tag using bridge-filtering
> (ebtables).

I also have a need to add the same physical port to multiple bridges, 
but my reason is different.

I have a block of static IP addresses, but instead of having a separate 
routing subnet for the gateway, my gateway has been placed on one of my 
own static IP addresses!  So, I need to have a bridge in order to do 
proper firewalling, since both filtered and unfiltered traffic must flow 
on the same subnet.

Here is my network:

eth0 = to gateway, raw unfirewalled IP packets
(IP address is on the same subnet as the rest of my static IP addresses)
      | br0
eth1 = to the rest of my machines on my static IP addresses

eth2 = additional machines on private IP addresses (via NAT)
(on a completely different subnet, using private IP addresses)

I have successfully firewalled my other static IP addresses by bridging 
eth0 and eth1 together into br0.  This works beautifully.  None of my 
machines have connection problems, and they are being defended by a 

However, for gaming purposes, I'd like to bridge eth1 and eth2 also 
together.  This is because non-IP protocols (such as IPX/SPX, used by 
many games) are not routed across the subnets.

What would be really neat is if I could filter by protocol:
     IP on eth1 = bridge to eth0/eth1
Non-IP on eth1 = bridge to eth1/eth2

I don't think the current bridging code supports this.

A workaround would be to find (or write) a simple utility that listens 
to all non-IP packets coming in on both eth1 and eth2, and blindly 
echoes the raw packets onto the other interface, so that the two 
interfaces effectively become bridged with regards to non-IP packets. 
This would be all done in userspace, so as not to interfere with the 
kernel bridging code.  Does such a program already exist?


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