Last Updated on August 7, 2021 by Admin 3
On Cisco switches, what is the correct order of port transition through the Spanning Tree Protocol (STP) states?
- learning, listening, blocking, forwarding
- listening, blocking, forwarding, learning
- blocking, learning, forwarding, listening
- blocking, listening, learning, forwarding
There are five states in STP transition:
After STP initialization, a port moves from blocking to listening, then to learning, and finally into forwarding state. In case of any errors or exceptions, a port may enter into a disabled state directly from any of the other four states. Once STP has fully converged, all ports on all switches will be in either a forwarding state or a blocking state. All other port states are transitioning states between blocking and forwarding.
When STP is initialized, all ports start in the blocking state to prevent bridge loops. If a switch determines that a blocking port must transition to a forwarding state, the blocked port will first move into a listening state, where it begins sending Bridge Protocol Data Units (BPDUs). Next, the port will transition to a learning state, which allows it to populate its Media Access Control (MAC) address table with addresses learned on the port, but it does not yet forward data frames. Finally, it moves into the forwarding state, where the port is capable of sending and receiving data. The switch only learns MAC addresses during the learning and forwarding states.
LAN Switching Fundamentals
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