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Which three statements are true regarding a topology change reconvergence scenario? (Choose three.)

You recently implemented a Layer 2 network using RSTP. Which three statements are true regarding a topology change reconvergence scenario? (Choose three.)

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A.
Switches do not flush MAC addresses learned from edge ports.

B.
When a port transitions to the discarding state on edge or nonedge ports, TCNs are generated and flooded.

C.
When a port transitions to the forwarding state on nonedge ports, the local switch generates and floods TCNs.

D.
Switches do not flush MAC addresses learned through the same port through which TCNs are received.

E.
When a port transitions to the forwarding state on edge ports, the local switch generates and floods TCNs.

Explanation:
RSTP decouples the states and roles of ports. It uses fewer port states than STP: discarding, learning, and forwarding. It also introduces two additional port roles for a total of five: designated, alternate, backup, and disabled. RSTP provides faster convergence time than the original STP. It identifies certain links as point-to-point and uses protocol handshake messages rather than fixed timeouts. When a point-to-point link fails, the alternate link can transition to the forwarding state without waiting for any protocol timers to expire and bypassing port states. Note that with RSTP (as with STP), all VLANs belong to the same spanning-tree instance.

For more information:
http://blog.ine.com/wp-content/uploads/2010/04/understanding-stp-rstp-convergence.pdf


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