On Thu, 2 Mar 2006, Sylvain Coutant wrote:

> First, regarding Carp and STP what happens usually in a manageable L2
> switch when the same MAC is announced on two different ports ? I don't
> remember that STP includes loadsharing, so isn't it possible the switch
> will only choose one port to forward on ? Please excuse me if it sounds
> stupid and just explain why ;-)

STP does not concern itself with MAC addresses of 
end-stations/ hosts / devices. It uses the MAC addresses within the
networking elements that run STP to look for (and make) a loop-free
network. So you problem will not be a strict STP issue.

The problem you will/may encounter will differ based on the vendor of
SWITCH1 and SWITCH2. Some vendors will handle it OK if the MAC is a 
multicast MAC, some will log a warning, some will not allow it and simple 
accept the first port, some will forward randomly.

This is a pure vendor-implementation issue of how they forward frames 
and if their CAM/FDB/Forwarding Database/whatever they call it allows
multiple entries and if it expires entries on ports that go down.

> switches, themselves connected together through one port. That setup

 With all that attention to redundacy, why not make the link between 
 SWITCH1 and SWITCH2 two links or more? 

> Once again, how will spanning tree handle this case with the same MAC
> announced from the 4 firewalls ? My guess is packets from SRV1 will be
> dispatched to FW1* because the cost will be lower. Same for SRV2/FW2*.

 Not an STP issue, a frame-forwarding issue on the switch. STP is not 
 involved in end-user traffic forwarding.

 If you have a relationship with the vendor, ask them. Or simply try
 it out and report back!


cheers,
--
jason

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