STP Clinical & Scientific Knowledge 5

Question 1

What is a unidirectional link failure and which STP feature is designed to detect it?

Accepted Answer

A fiber link where one direction fails, detected by UDLD

Answer

UDLD (Unidirectional Link Detection) detects fiber links where traffic flows in only one direction, which STP cannot detect and which can cause loops.

Question 2

In STP, what is the total default convergence time when a direct link to the root bridge fails?

Accepted Answer

50 seconds

Answer

Default STP convergence is MaxAge (20s) + 2× Forward Delay (2×15s) = 50 seconds.

Question 3

Which STP feature is specifically designed to speed up convergence when an indirect failure (non-direct path) to the root occurs?

Accepted Answer

BackboneFast

Answer

BackboneFast reduces convergence time for indirect failures by immediately expiring MaxAge and sending Root Link Queries (RLQs).

Question 4

A switch running PVST+ has 100 VLANs configured. How many STP instances is it running?

Accepted Answer

100

Answer

PVST+ runs one independent STP instance per VLAN, so 100 VLANs means 100 separate spanning tree processes.

Question 5

What is the purpose of Root Guard in STP?

Accepted Answer

Prevents a designated port from accepting superior BPDUs that would make the connected switch root

Answer

Root Guard prevents a port from becoming a root port by placing it in root-inconsistent state if a superior BPDU is received.

(STP) Spanning Tree Protocol Practice Test

(STP) Spanning Tree Protocol Practice Test

STP Clinical & Scientific Knowledge 5