Rich Seifert's "The Switch Book" describes a way for a switch to
implement VLANs: the forwarding table is the same as that for a
VLAN-unaware switch, but before forwarding a frame the switch checks
that the outgoing port is a member of the frame's VLAN. This seems to
me to be a kludge that allows a switch to have VLAN capability added
without changing the forwarding table implementation.
The Cisco switches that I have access to do things differently. I can
see the difference if I use the same MAC address in different VLANs.
The switches I have tested allow the same MAC address to map to
different ports on different VLANs.
For reasons I can't explain right now, the distinction is important to
me. The question is, how many switches out there implement VLANs in
the way described in Rich's book? I am interested both any currently
shipping switches do it that way, and what fraction of the installed
base of switches do it that way.