Linux Ethernet Bridging - Aug 2007 - [Bridge] bridge problem when one interface is in blocking mode

Hi,

We have a simple bridge setup but the ping (and other
network traffic) does not work reliably. After tracing
the code, it looks like a software bug. Since bridge
software is been running by thousands of people. I
guess I am wrong.  Anyway, here is the problem.

There are 2 boxes and each one has 2 interfaces, 1
ethernet and 1 wifi. STP is enabled for the bridge to
avoid the loop. So the box 1 has wifi in the blocking
mode. When we ping from box 1 to box 2, lots of
packages lost. Ping from box 2 to box 1 does not has
this problem. 

After we tracing the code, we noticed that the box try
to using wifi to send the packages which is in
blocking mode. This happens because the ath0 is
returned from the forwarding database. It's
implemented in __br_fdb_get(br, dest). 
>From the etherreal, I noticed, that the STP package is
broadcast from the box 2. From the function
br_handle_frame(), if a stp package is received, it
will update the forwarding database. Since the STP
package is sent/received by both interfaces, the wifi
(blocking) received the package and update the
forwarding database too. So, __br_fdb_get() will
returns the wifi card sometimes. And then, the package
is lost. 

Regards,

Dengyi Wang







       
____________________________________________________________________________________
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Sims Stories at Yahoo! Games.
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On Wed, 22 Aug 2007 15:36:30 -0700 (PDT)
wang dengyi <dy_wang@yahoo.com> wrote:
> Hi,
> 
> We have a simple bridge setup but the ping (and other
> network traffic) does not work reliably. After tracing
> the code, it looks like a software bug. Since bridge
> software is been running by thousands of people. I
> guess I am wrong.  Anyway, here is the problem.
> 
> There are 2 boxes and each one has 2 interfaces, 1
> ethernet and 1 wifi. STP is enabled for the bridge to
> avoid the loop. So the box 1 has wifi in the blocking
> mode. When we ping from box 1 to box 2, lots of
> packages lost. Ping from box 2 to box 1 does not has
> this problem. 
> 
> After we tracing the code, we noticed that the box try
> to using wifi to send the packages which is in
> blocking mode. This happens because the ath0 is
> returned from the forwarding database. It's
> implemented in __br_fdb_get(br, dest). 
> 
> >From the etherreal, I noticed, that the STP package is
> broadcast from the box 2. From the function
> br_handle_frame(), if a stp package is received, it
> will update the forwarding database. Since the STP
> package is sent/received by both interfaces, the wifi
> (blocking) received the package and update the
> forwarding database too. So, __br_fdb_get() will
> returns the wifi card sometimes. And then, the package
> is lost. 
> 
> Regards,
> 
> Dengyi Wang
What kernel version are you using?

Bridging over wifi doesn't usually work unless the wifi driver
has WDS support.  In wifi when bridging the driver would need
to add an additional header that gives intermediate hop information:
See:
	http://www.cisco.com/en/US/docs/wireless/access_point/1300/12.2_15_JA/configuration/guide/o13wds.html

> 
> 
> 
> 
> 
> 
>        
>
____________________________________________________________________________________
> Moody friends. Drama queens. Your life? Nope! - their life, your story.
Play Sims Stories at Yahoo! Games.
> http://sims.yahoo.com/  
> _______________________________________________
> Bridge mailing list
> Bridge@lists.linux-foundation.org
> https://lists.linux-foundation.org/mailman/listinfo/bridge

-- 
Stephen Hemminger <shemminger@linux-foundation.org>

On Thu, Aug 30, 2007 at 12:22:58PM -0700, Stephen Hemminger
wrote:
> This patch fixes some packet leakage in bridge.  The bridging code
> was allowing forward table entries to be generated even if a device
> was being blocked. The fix is to not add forwarding database entries
> unless the port is active.
Seems reasonable -- ACK

John
-- 
John W. Linville
linville@tuxdriver.com

From: "John W. Linville" <linville@tuxdriver.com>
Date: Thu, 30 Aug 2007 16:03:13 -0400
> On Thu, Aug 30, 2007 at 12:22:58PM -0700, Stephen Hemminger wrote:
> > This patch fixes some packet leakage in bridge.  The bridging code
> > was allowing forward table entries to be generated even if a device
> > was being blocked. The fix is to not add forwarding database entries
> > unless the port is active.
> 
> Seems reasonable -- ACK
Applied, thanks.