[Bridge] Minimal transparent bridge

Jim Lloyd jim.lloyd at mac.com
Fri Jun 2 10:28:21 PDT 2006


Hello again,

I didn't see any response to my questions below. Can someone at least  
confirm or deny that bridging is still broken (or not) with 2.6 kernels?

Thanks in advance,
Jim Lloyd

On May 31, 2006, at 7:10 PM, Jim Lloyd wrote:

> Hi folks,
>
> I have some ambitious plans to set up a Fedora Core 5 node as a
> transparent bridge between my host's gateway and the remainder of a
> rack of nodes colocated at the host that I share with some friends.
> I've had a hard time getting this working. I seem to be stuck at a
> pretty basic level, so I am hoping there is something obvious someone
> can point out for me. For example, I just noticed one warning against
> using 2.6 kernels. Is that still true, even for the most current 2.6
> kernels (2.6.16.1)?
>
> I'd like to start with a very simple question: what is the minimal
> steps to set up a server with two ethernet interfaces (eth0 and eth1)
> as a transparent bridge?
>
> I'm following the Nils Radtke's how-to here:
> http://www.tldp.org/HOWTO/Ethernet-Bridge-netfilter-HOWTO.html
>
> Assume I have a 3 node network:
>
> L:eth0 <-> eth0:B:eth1 <-> eth0:R
>
> B is my bridge. L and R are nodes on the same subnet that can ping
> each other if the bridge is replace by a hub.
>
>  From what I know so far, I thought the following steps on the bridge
> should be enough:
>
> 1) remove all iptable rules.
> 2) do the following
>
>      (ifdown eth0 1>/dev/null 2>&1;);
>      (ifdown eth1 1>/dev/null 2>&1;);
>      brctl addbr br0;
>      brctl stp br0 on;
>      brctl addif br0 eth0;
>      brctl addif br0 eth1;
>      ifconfig eth0 0.0.0.0 up;
>      ifconfig eth1 0.0.0.0 up;
>      ifconfig br0  up
>
> The above commands are taken from <http://www.tldp.org/HOWTO/Ethernet-
> Bridge-netfilter-HOWTO-3.html#ss3.3>, but reordered and stripped
> down. Note in particular I don't assign the br0 interface an ip  
> address.
>
> After doing the above, should I be able to once again ping R from L
> and vice versa? Or is setting proxy_arp and forwarding required?
>
>      for file in br0 eth0 eth1;
>      do
>        echo "1" > /proc/sys/net/ipv4/conf/${file}/proxy_arp;
>        echo "1" > /proc/sys/net/ipv4/conf/${file}/forwarding;
>      done;
>      echo "1" > /proc/sys/net/ipv4/ip_forward;
>
>  From reading Nils's how-to, these steps seem to be necessary.
> However, the bridge wiki page doesn't mention them <http://linux-
> net.osdl.org/index.php/Bridge>, and another page makes it seem like
> they might only be necessary for "pseduo-bridges": <http://lartc.org/
> howto/lartc.bridging.proxy-arp.html>.
>
> Thanks in advance for any answers.
>
> Jim Lloyd
>
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