Cisco CCNA Spanning Tree Protocol (STP) 3

Question 1

Which Rapid STP (802.1w) port role replaces the STP blocking state and provides an alternate path to the root bridge?

Accepted Answer

Alternate port

Answer

In RSTP, the Alternate port is in the Discarding state and provides a redundant path to the root bridge if the root port fails.

Question 2

What is the purpose of the STP Topology Change Notification (TCN) BPDU?

Accepted Answer

To inform other switches that the Layer 2 topology has changed so MAC tables can be flushed

Answer

TCN BPDUs signal topology changes so that switches reduce their MAC address aging timer to quickly flush stale entries.

Question 3

A network has three switches with default bridge priorities. Switch A has MAC 00:00:00:00:00:01, Switch B has MAC 00:00:00:00:00:02, and Switch C has MAC 00:00:00:00:00:03. Which switch becomes the root bridge?

Accepted Answer

Switch A

Answer

With equal priorities, the switch with the lowest MAC address wins; 00:00:00:00:00:01 is the lowest, making Switch A the root bridge.

Question 4

Which STP port state is equivalent to the RSTP 'Discarding' state?

Accepted Answer

Blocking

Answer

RSTP combines the STP Blocking and Listening states into a single Discarding state where neither forwarding nor MAC learning occurs.

Question 5

What is the STP path cost for a 1 Gbps link using the IEEE 802.1D-2004 revised cost values?

Accepted Answer

4

Answer

The revised IEEE 802.1D-2004 cost for a 1 Gbps link is 4, while the original 1998 standard assigned it a cost of 4 as well (but 10 Gbps=2, 100 Mbps=19).

Cisco CCNA Practice Test

Cisco CCNA Practice Test

Cisco CCNA Spanning Tree Protocol (STP) 3