[Bridge] STP on Linux 2.6.30.9

[Stephen Hemminger]

On Thu, 07 Jan 2010 17:57:16 -0600
Andrew <amckay at iders.ca> wrote:

> Hey guys,
> 
> I'm working with a bridge I set up on Linux 2.6.30.9.  I have two boards 
> connected and created a redundant connection between them.  Basic set up is:
> 
> brctl addbr br0
> brctl addif br0 vlan1
> brctl addif br0 vlan2
> brctl stp br0 on
> 
> Then I bring up the interfaces.  Everything seems to be fine.  Root 
> bridge is negotiated properly and leaves both interfaces in forwarding 
> mode.  The other bridge leaves one port in forwarding and puts the other 
> in blocking mode.  However after several seconds a message is printed on 
> my terminal saying that vlan2 lost it's neighbor and goes through the 
> listening, learning and then forwarding states.  It then quickly flips 
> back to blocking mode.  Is this normal behavior for STP on Linux 
> 2.6.30.9?  Or do I have something else going on here?
> 
> net/bridge/br_stp.c:36 br0: port 2(vlan2) entering blocking state
> br0: neighbor 8000.3a:1f:34:08:54:56 lost on port 2(vlan2)
> net/bridge/br_stp.c:36 br0: port 2(vlan2) entering listening state
> net/bridge/br_stp.c:36 br0: port 2(vlan2) entering learning state
> br0: topology change detected, sending tcn bpdu
> net/bridge/br_stp.c:36 br0: port 2(vlan2) entering forwarding state
> br0: topology change detected, sending tcn bpdu
> net/bridge/br_stp.c:36 br0: port 2(vlan2) entering blocking state
> 
> If there's any further information you need, let me know.

Bridging two vlan's with STP can be problematic because many
switches implement STP on a physical interface (see vlan Spanning
Tree). Also, make sure that STP packets aren't being blocked by
some firewall rule.