[Bridge] Link fail over - bridge slow learning !?!

[Alex Zeffertt]

It still uses a forwarding delay.  Try "brctl setfd br0 1" to set it to
1 second.

Alexander Indenbaum wrote:
> Alex,
> 
> That was my first thought too, but STP is disabled.
> 
> On 10/11/06, Alex Zeffertt <ajz at cambridgebroadband.com> wrote:
>> Alexander Indenbaum wrote:
>> > Hello,
>> >
>> > I'm playing with dual-port NIC driver level link failover:
>> > * Driver exposes single network interface to the OS and operates both
>> > ports in active-passive failover mode.
>> > * Upon Link down event on active port, driver switches active and
>> > passive ports transparently for the OS.
>> >
>> > I'm testing the driver using Linux bridge module: "failover" dual-port
>> > NIC connected with two cables back-to-back to eth0 and eth1 which are
>> > part of br0 bridge.
>> >
>> > I simulate link fail with following scenario:
>> > * At t0 both eth0 and eth1 port links are UP, traffic is accepted by
>> > eth0 and forwarded to br0
>> > * At t1 I manually unplug eth0 cable, causing link to go down.
>> > "Failover" driver switches the traffic immediately from eth0 to eth1,
>> > while using the same MAC address.
>> > * From t1 till t1+12 secs packets are accepted by eth1 but dropped by
>> > bridge and not forwarded to br0.
>> > * At t1+12 secs bridge starts forwarding packets from eth1 to br0
>> >
>> > Hmm... I would expect that eth0 link down event would flush from
>> > bridge's table any MAC address associated with the port and that the
>> > bridge would start forwarding packets from eth1 to br0 immediately.
>> >
>> > Why does it take ~12 secs for bridge to learn that MAC address moved
>> > from eth0 to eth1 in the described scenario?
>> >
>>
>> It may be spanning tree, rather than MAC address learning that takes
>> so long.  Bridges spend a while just listening before forwarding, to
>> avoid becoming part of a bridging loop.
>>
>> Experiment with:
>>
>>    brctl showstp br0
>>    brctl stp br0 off
>>    brctl setfd br0 1
>>
>> Alex
>>
>>
> 
>