❑ STP(Spanning Tree Protocol) : A OSI 2 layer protocol that prevents looping due to flooding traffic. This is implemented by communicating BPDU frames between network equipments.
❑ The procedure of applying STP : In order to be operated STP, it is necessary to go through the following procedure.
* Switch#show spanning-tree : Check election results of root bridge and ports.
1. Elect the root bridge(Root switch) : The switch with the lowest BID among the switches in the same network is selected as the root bridge.
* BID : priority + MAC address
2. Elect the root port : All switches elect one of their ports as the root port.
A) Priority for electing root port
1) The port with closest to the root bridge.
2) The port with the lowest path cost to the root bridge(Based on port).
3) The port with the lowest BID of the adjacent switch.
4) The port with the lowest port ID of the adjacent switch.
5) The port with the lowest port ID.
3. Elect designated port : One designated port per segment is elected
* segment : A line connected between devices).
A) Priority for electing designated port
1) The port connected to the root port.
2) Non-root port.
3) The port with lowest path cost(Based on switch).
4) The port with a lower BID.
5) The port with a lower port ID.
4. Elect alternate port(non designated port) : The remaining port that have not been elected to the designated port in the segment.