[c-nsp] MAC address for SVIs on 3550

[Phillip Vandry]

Hello,

The following document makes clear the fact that the Catalyst 3550 does
not support using a unique MAC address on each Vlan interface:

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00801c9b4e.shtml

What's not explained in the document and what I'd like to understand
better is where the one common MAC address shared between all Vlan
interfaces comes from.

I have one 3550 where the MAC address for each Vlan also happens to
be shared with GigabitEthernet0/1 (and all the other ports have a
unique address). A different 3550 has the shared MAC address on
fast ethernet port 24. Yet another 3550 has the shared MAC address
only being shared among the Vlan interfaces - all the physical
ports then have their own MAC addresses.

Is there a rule?

-Phil