Spanning Tree Protocol part 3

Find the Root Bridge

1. Find the root bridge with the lowest priority or MAC address. Sometimes called the Bridge ID.
2. All the active ports on the Root Bridge become designated ports.


Find the Root ports (One RP per switch)

1. Lowest cost to Root Bridge.
2. Lowest neighbor Bridge ID
3. Lowest neighbor port priority
4. Lowest neighbor internal port number.



Finding the Designated ports for LAN segments.

1. Between non-root switch segments, find the switch that has the lost cost to the root bridge.
2. Lowest BID
3. Lowest neighbor port priority (Rare)
4. Lowest neighbor internal port number. (Rare)


STP Costs
1. 100 for 10Mbps
2. 19 for 100Mbps
3. 4 for 1Gbps
4. 2 for 10Gbps