STP Port States and Roles 1 — Questions and Answers
Question 1: How many port states exist in the original IEEE 802.1D Spanning Tree Protocol?
- 3
- 4
- 5 (Correct answer)
- 6
Correct answer: 5
IEEE 802.1D STP defines five port states: Blocking, Listening, Learning, Forwarding, and Disabled.
Question 2: In which STP port state does a switch port learn MAC addresses but NOT forward data frames?
- Blocking
- Listening
- Learning (Correct answer)
- Forwarding
Correct answer: Learning
In the Learning state, the port populates the MAC address table but still does not forward data frames to prevent loops.
Question 3: A port in the Blocking state will do which of the following?
- Forward data frames and send BPDUs
- Receive BPDUs but not forward data frames (Correct answer)
- Learn MAC addresses and forward BPDUs
- Neither send nor receive any traffic
Correct answer: Receive BPDUs but not forward data frames
A Blocking port listens to BPDUs to stay informed about the STP topology but discards all data frames to prevent loops.
Question 4: What is the default duration of the Listening state in IEEE 802.1D STP?
- 5 seconds
- 10 seconds
- 15 seconds (Correct answer)
- 20 seconds
Correct answer: 15 seconds
The Listening state lasts for one Forward Delay period, which defaults to 15 seconds in IEEE 802.1D.
Question 5: Which STP port state is functionally equivalent to the Discarding state introduced in RSTP (802.1w)?
- Forwarding
- Learning
- Listening
- Blocking (Correct answer)
Correct answer: Blocking
RSTP's Discarding state consolidates 802.1D's Blocking and Listening states, where the port neither learns MAC addresses nor forwards frames.
Question 6: In which two STP port states does a port actively participate in sending and receiving BPDUs? (Choose the pair that applies)
- Blocking and Disabled
- Listening and Forwarding (Correct answer)
- Learning and Disabled
- Disabled and Forwarding
Correct answer: Listening and Forwarding
Ports in the Listening and Forwarding states actively send and receive BPDUs; Blocking only receives them, and Disabled does neither.
Question 7: What total time does a port transitioning from Blocking to Forwarding take by default in IEEE 802.1D?
- 15 seconds
- 20 seconds
- 30 seconds (Correct answer)
- 50 seconds
Correct answer: 30 seconds
A port passes through Listening (15 s) and Learning (15 s) states, totaling 30 seconds before reaching the Forwarding state.
STP Port States and Roles 1
How many port states exist in the original IEEE 802.1D Spanning Tree Protocol?