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

[Alexander Indenbaum]

On 10/11/06, Alex Zeffertt <ajz at cambridgebroadband.com> wrote:
> It still uses a forwarding delay.  Try "brctl setfd br0 1" to set it to
> 1 second.

Thanks Alex. It did the trick.
Could you explain why?

>
> 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
> >>
> >>
> >
> >
>
>


-- 
Alexander Indenbaum