STP Basics and Concepts 2 — Questions and Answers
Question 1: Which STP port state forwards data frames AND learns MAC addresses?
- Blocking
- Listening
- Learning
- Forwarding (Correct answer)
Correct answer: Forwarding
Only the Forwarding state both learns MAC addresses and forwards data frames across the network.
Question 2: What is the default STP bridge priority value on a Cisco switch?
- 0
- 4096
- 32768 (Correct answer)
- 65535
Correct answer: 32768
Cisco switches default to a bridge priority of 32768, which is the midpoint of the 0–65535 range.
Question 3: Which field in the Bridge ID is used to differentiate switches with the same base priority?
- Port cost
- MAC address (Correct answer)
- Hello timer
- VLAN ID
Correct answer: MAC address
When bridge priorities are equal, the lowest MAC address breaks the tie to elect the root bridge.
Question 4: What happens to a non-root switch port that receives a superior BPDU?
- It becomes a designated port
- It becomes a root port (Correct answer)
- It transitions to Forwarding immediately
- It sends a TCN BPDU
Correct answer: It becomes a root port
A port that receives the best BPDU from the root bridge direction becomes the root port for that switch.
Question 5: What is the STP port cost for a 1 Gbps link using the original IEEE cost values?
- 1
- 4 (Correct answer)
- 19
- 100
Correct answer: 4
The original IEEE 802.1D cost for a 1 Gbps link is 4, based on the formula 1000/bandwidth in Mbps.
Question 6: Which STP timer controls how long a port waits in the Listening and Learning states?
- Hello time
- Forward delay (Correct answer)
- Max age
- Hold time
Correct answer: Forward delay
The forward delay timer (default 15 seconds) determines the duration spent in each of the Listening and Learning states.
Question 7: In STP, what is the role of a designated port on a network segment?
- It is the port closest to the root bridge
- It blocks all traffic on that segment
- It forwards frames toward the root bridge
- It is the single forwarding port on each segment (Correct answer)
Correct answer: It is the single forwarding port on each segment
Each LAN segment has exactly one designated port, which is the forwarding port responsible for that segment's traffic toward the root.
STP Basics and Concepts 2
Which STP port state forwards data frames AND learns MAC addresses?