ICND1 Spanning Tree Protocol (STP) 2 — Questions and Answers
Question 1: On a non-root switch, which port provides the best path toward the Root Bridge?
- Designated Port
- Blocked Port
- Root Port (Correct answer)
- Alternate Port
Correct answer: Root Port
Each non-root switch has exactly one Root Port, which is the port with the lowest accumulated path cost to the Root Bridge.
Question 2: The Bridge ID used in STP elections is composed of which two elements?
- IP address and subnet mask
- Bridge priority and MAC address (Correct answer)
- VLAN ID and port number
- Switch hostname and serial number
Correct answer: Bridge priority and MAC address
The 8-byte Bridge ID combines a 2-byte configurable bridge priority and the 6-byte MAC address burned into hardware.
Question 3: What is the IEEE STP path cost assigned to a 100 Mbps Fast Ethernet link?
- 4
- 19 (Correct answer)
- 100
- 1000
Correct answer: 19
The IEEE 802.1D long-mode STP path cost for a 100 Mbps Fast Ethernet link is 19; lower bandwidth results in higher cost.
Question 4: What is the default value of the STP Forward Delay timer?
- 5 seconds
- 10 seconds
- 15 seconds (Correct answer)
- 20 seconds
Correct answer: 15 seconds
The Forward Delay timer defaults to 15 seconds and applies to both the Listening state and the Learning state.
Question 5: Which STP port state receives BPDUs but blocks all user data traffic?
- Forwarding
- Blocking (Correct answer)
- Learning
- Disabled
Correct answer: Blocking
A port in Blocking state receives and processes BPDUs to remain aware of topology changes but discards all user data frames.
Question 6: What primarily determines which switch becomes the Designated Switch on a network segment?
- The switch with the highest bridge priority on the segment
- The switch with the lowest path cost to the Root Bridge (Correct answer)
- The switch with the highest MAC address on the segment
- The switch that was powered on most recently
Correct answer: The switch with the lowest path cost to the Root Bridge
The Designated Switch on each segment is the one with the lowest accumulated path cost to the Root Bridge, with Bridge ID as the tiebreaker.
Question 7: What is the default STP Max Age timer value?
- 5 seconds
- 10 seconds
- 15 seconds
- 20 seconds (Correct answer)
Correct answer: 20 seconds
The Max Age timer defaults to 20 seconds; after this period without receiving a BPDU, a switch discards stored BPDU information and initiates a topology change.
ICND1 Spanning Tree Protocol (STP) 2
On a non-root switch, which port provides the best path toward the Root Bridge?