[Bridge] LAN-WAN Bridging Problem

Stephen Hemminger shemminger at linux-foundation.org
Wed Jan 24 13:30:52 PST 2007

On Wed, 24 Jan 2007 09:30:41 -0800
Michael Boutte <mboutte at pacbell.net> wrote:

> Hello,
> I am experiencing what may be a unique problem with operating the 
> bridge. My hardware is custom Freescale MPC875 processor based with one 
> ethernet (eth0) and one hdlc (hdlc0) WAN port and I am connecting two of 
> these boards together using the WAN ports over a long distance - 
> essentially two bridges in series.  They are running Linux 2.6.15 with 
> bridging enabled in the kernel configuration. When I first power up both 
> boards the bridge comes up fine and the two outside LANs are connected 
> as if it were one LAN with a smart long cable in between. brctl works to 
> set it up and the "showmacs" properly shows all of the MACs on each end.
> The problem occurs If I disconnect the ethernet cable directly from the 
> bridge at either end. The console on the disconnected units says "br0: 
> port 2(eth0) entering disabled state". When I reconnect the cable it 
> shows "br0: port 2(eth0) entering learning state" plus messages about 
> network topology change detected. That LAN end no longer has a link to 
> the other end, yet at the console of the unit disconnected and 
> reconnected I can ping in either direction to any device in both LAN 
> segments. Time makes no difference, but if I issue the command "ifconfig 
> eth0 down" and then back "up" the link is almost immediately restored. 
> This works either while the cable is disconnected or after it is 
> reconnected.
> I compared the effect of a cable disconnect with a standard PC running 
> Linux and it seems to be identical, that is, ifconfig shows the port as 
> up even when the cable is disconnected on both. I tried having STP 
> enabled or disabled, and adding the ports into br0 in the opposite order 
> with no difference either. Any ideas on why the bridge does not 
> automatically restore? and especially on how I can make it automatically 
> restore itself?
> Thank you for your kind attention.
> Mike Boutte

You probably don't want the forwarding delay period (30 seconds)
that occurs on link transitions. Use:
	brctl setfd br0 0

Stephen Hemminger <shemminger at linux-foundation.org>

More information about the Bridge mailing list