CCNP/CCDP Switching (642-813) practice questions: Spanning Tree port states

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Q5. Which Spanning-Tree port state allows addition of information that a switch port has learned, to its address table?

         A. Listen

        B. Learn

        C. Forward

        D. Disabled

Correct Answer: B

Explanation: 

A switch, participating in Spanning-Tree protocol, passes through the following states:
1. Blocked state: This is the initial state. All ports are put in a blocked state to prevent bridging loops. 
2. Listen state: This is the second state of switch ports. Here all the ports are put in listen mode. The port can listen to frames but can't send. The period of time that a switch takes to listen is set by "fwd delay" . 
3. Learn state: Learn state comes after Listen state. The only difference is that the port can add information that it has learned to its address table. The period of time that a switch takes to learn is set by "fwd delay". 
4. Forward state: A port can send and receive data in this state. Before placing a port in forwarding state, Spanning-Tree Protocol ensures that there are no redundant paths or loops.
5. Disabled state: This is the state when the switch port is disabled. A switch port may be disabled due to administrative reasons or due to switch specific problems.

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