CompTIA Network+ (N10-009)Network ImplementationMedium
A switch port running Spanning Tree Protocol has just been enabled and is currently examining incoming BPDUs to determine its role in the topology, but it is not yet forwarding user traffic or learning MAC addresses. Which STP port state is this?
- ALearning
- BListening
- CBlocking
- DForwarding
Show answer & explanationAnswer & explanation
Correct answer: B. Listening
In the Listening state, the port processes BPDUs to participate in topology calculation but does not yet learn MAC addresses or forward frames. This follows Blocking and precedes Learning, where MAC learning begins, and Forwarding, where actual data traffic flows.
Why the other options are wrong
- A. Learning state builds the MAC address table but still does not forward frames.
- C. Blocking discards all frames including BPDUs used for topology calculation are still received, but no active participation occurs beyond that.
- D. Forwarding is the final state where the port both learns addresses and forwards frames.
STP Port States
Spanning Tree Protocol progresses ports through Blocking, Listening, Learning, and Forwarding states to prevent loops while building a loop-free topology.
- Blocking: no forwarding, no learning, receives BPDUs
- Listening: processes BPDUs, no learning/forwarding
- Learning: builds MAC table, no forwarding
- Forwarding: full data traffic flow
Memory trick: Blocking, Listening, Learning, Forwarding — BLLF, the loop-free march.