First the root bridge will be selected based on the lowest Bridge ID (made of 2bytes priority and MAC address of the bridge). Once the root is slected other switches have to decide how they will get to the bridge. The parameters used are in the order:
1. Port-cost (lowest better) - This is as seen from the access switches towards the root.
2. Port-priority (lowest better) - Advertised by the root and affects downstream switches.
3. Port-ID (lowest better)- When you look at the output of show spann, for f0/4 you will see something like 128.4. 128 is the port priority and 4 is the port ID. See output below.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...