Spanning Tree Protocol (STP) Flashcards

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

Answer: Alternate port

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

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

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

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

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?

Answer: Switch A

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.

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

Answer: Blocking

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

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

Answer: 4

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).

Which command verifies the STP role and state of all ports on a Cisco switch for VLAN 10?

Answer: show spanning-tree vlan 10

The 'show spanning-tree vlan 10' command displays the root bridge, bridge priority, port roles, port states, and costs for VLAN 10.

Which RSTP port type connects to another switch's designated port and can achieve rapid transition to Forwarding?

Answer: Point-to-point port

RSTP point-to-point ports (full-duplex links to other switches) can negotiate rapid transitions using the proposal/agreement mechanism.