1. Lowest bridge ID (Priority:MAC Address) switch becomes the Root-Bridge
2. Each non-root bridge should have ONE root port (RP) which is the port having lowest path-cost to Root Bridge.
If the path cost equal, then here are the criteria:
- 1. Lowest Sending Bridge ID
- 2. Lowest Port Priority (of sender)
- 3. Lowest Interface number (of sender)
3. All ports in Root Bridge become Designated Ports (DP)
4. Each segment should have one Designated Port (DP)
5. All RP/DPs will be in FORWARDING state & all other ports will be in BLOCKING state.
You may wish to look at this animation:
You can see some detail here also: