[c-nsp] Same MAC addresses from two ports on different VLAN

[Tim Durack]

On Fri, Mar 12, 2010 at 2:21 PM, Jay Nakamura <zeusdadog at gmail.com> wrote:
> We have an Extreme Summit switch where I found that if you have two
> separate ports on different VLANs, and the same MAC address enters the
> switch on those two completely different VLANs, the switch will start
> having problems forwarding traffic.  (Or only use the first entry in
> the FDB, I am not sure what it actually does other than half of the
> traffic drops.)  Extreme support has confirmed that this is by design.
>
> The reason I am posting this here is simple, does Cisco switches do
> the same thing?  Or if MAC address comes from two ports on different
> VLAN, would it just forward per VLAN?  Or would it depend on the
> model?
>
> I can think of so many possible problems with this that I want to see
> if this is common design of switches or just Extreme and I need to
> start using different L2 switches.

I have run into it multiple times on some older (circa 2000) ProCurve
equipment. Modern switches should have per-vlan fdb, avoiding this
problem.

-- 
Tim:>