Introduction to Spanning-Tree

Hello Andrew!

Actually, the information that is displayed after the word “Port” in the output in your post indicates which port on the switch is the root port for VLAN 1.

Notice it says GigabitEthernet0/1 in brackets. That’s the port using the typical designations we use to identify ports on a switch. However, STP uses an internal port reference number to identify ports, and that is what the number “2” here signifies. These STP port numbers are assigned in sequential order to all ports on a switch including management ports, fixed and modular physical ports, as well as virtual ports (SVIs) and tunnel ports.

How these numbers are assigned depends upon the platform and IOS version, and the configuration of any modular components of the switch.

These port numbers are an important part of STP as they also play a tie-breaking role in determining which port will be blocked. This is especially the case when two switches have multiple links between them, as shown at the end of this lesson. This number is the ultimate tiebreaker in such cases. Does that make sense?

I hope this has been helpful!