Hi. I just wish to ask if rstp on a trunk interface works in a forwarding or discarding state as per vlan or does it forward all vlans on one trunk interface and discards on another. I mean if i have interface f0/1 and f0/2 on a non-root switch and vlan 1 cost is less on f0/1 and vlan 2 cost is less on int f0/2, does this mean that f0/1 will be forwarding vlan 1 and discarding vlan2 while f0/2 will be forwarding vlan2 and discarding vlan 1?
RSTP is done on a per vlan basis so on a trunk interface one vlan could be in forwarding whilst another could be discarding. In fact this is quite a common setup as an access-layer switch connected to 2 distribution switches where the odd and even vlans are sent on different uplinks.