Could someone explain to me what is the different between the Port # and Fastinterface in the output below? This is the output generated after executing the sho spanningtree detail.
Thanks in advance,
Port 50 (FastEthernet0/46) of VLAN0001 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.50.
Designated root has priority 32768, address 0007.eb78.e390
Designated bridge has priority 32769, address 0014.1cec.3f80
Designated port id is 128.50, designated path cost 19
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
The port is in the portfast mode
Link type is shared by default
BPDU: sent 7393757, received 0
Port 50 is the port's spanning-tree identifier.
You can see it in the second row as well: Port identifier 128.50
128 is the port priority, 50 is the port identifier.
The port identifier is not necessarily tied to the port number (Fastethernet0/46 in this case). You don't have to worry about it.
It is used by the spanning-tree algorithm in specific cases as a tiebreaker, if multiple ports are candidates for the designated port role:
The port that receives the BPDU with the lowest sender port ID, will become the designated port, if all other prior decisive factors (root bridge ID, root path cost, sender bridge ID and sender port priority) are the same.