Spanning Tree Protocol (STP) Flashcards

Which STP port state forwards data frames but does NOT learn MAC addresses?

Answer: Listening

The Listening state participates in frame forwarding decisions but does not populate the MAC address table.

A switch has a bridge priority of 32768 and a MAC address of 00:1A:2B:3C:4D:5E. What is its Bridge ID?

Answer: 32768:00:1A:2B:3C:4D:5E

The Bridge ID is a combination of the bridge priority (2 bytes) followed by the MAC address (6 bytes).

What is the default STP forward delay timer value?

Answer: 15 seconds

The default forward delay is 15 seconds, which applies to both the Listening and Learning states.

Which type of STP port provides the best path from a non-root switch back toward the root bridge?

Answer: Root port

Each non-root switch has exactly one root port, which is the port with the lowest cost path to the root bridge.

In PVST+, how is the extended system ID used in the bridge priority field?

Answer: The VLAN ID is added to the bridge priority

PVST+ uses the lower 12 bits of the 16-bit priority field as the extended system ID (VLAN ID), so valid priorities must be multiples of 4096.

Which STP feature automatically sets a port to the Forwarding state when connected to an end device, bypassing the Listening and Learning states?

Answer: PortFast

PortFast allows a port to transition directly to Forwarding, skipping Listening and Learning, and is intended for ports connected to end hosts.

What happens when a switch running STP receives a superior BPDU on its root port?

Answer: It updates its root bridge information and may recalculate the topology

A superior BPDU (lower bridge ID) causes the switch to update its stored topology information and potentially trigger STP recalculation.