STP STP Fundamentals — Questions and Answers
Question 1: What is the primary purpose of Spanning Tree Protocol?
- To prevent Layer 2 switching loops in networks with redundant paths (Correct answer)
- To route IP packets
- To encrypt network traffic
- To manage DHCP addresses
Correct answer: To prevent Layer 2 switching loops in networks with redundant paths
STP prevents broadcast storms and MAC table instability by blocking redundant paths in switched networks.
Question 2: What is a bridge ID in STP?
- A combination of bridge priority and MAC address used to elect the root bridge (Correct answer)
- An IP address assigned to switches
- A physical label on the switch
- A VLAN identifier
Correct answer: A combination of bridge priority and MAC address used to elect the root bridge
The bridge ID consists of a priority value and the switches MAC address, determining which switch becomes the root bridge.
Question 3: What is the root bridge in STP?
- The switch with the lowest bridge ID that serves as the reference point for all path calculations (Correct answer)
- The switch with the most ports
- The fastest switch
- The newest switch on the network
Correct answer: The switch with the lowest bridge ID that serves as the reference point for all path calculations
The root bridge is elected based on having the lowest bridge ID and serves as the center of the spanning tree topology.
Question 4: What are the STP port states in 802.1D?
- Blocking, Listening, Learning, Forwarding, Disabled (Correct answer)
- Active, Inactive
- Open, Closed
- On, Off, Standby
Correct answer: Blocking, Listening, Learning, Forwarding, Disabled
802.1D STP uses five port states as ports transition from blocking to forwarding.
Question 5: What is the STP path cost?
- A value assigned to each port based on link speed, used to determine the best path to the root bridge (Correct answer)
- The price of the network cable
- The physical distance between switches
- The number of VLANs on a link
Correct answer: A value assigned to each port based on link speed, used to determine the best path to the root bridge
Path cost is inversely related to link speed - faster links have lower costs, making them preferred paths.
Question 6: How often does the root bridge send BPDUs?
- Every 2 seconds by default (hello timer) (Correct answer)
- Every 10 seconds
- Every 30 seconds
- Only once during initialization
Correct answer: Every 2 seconds by default (hello timer)
The root bridge generates hello BPDUs every 2 seconds, which are relayed by other switches to maintain the spanning tree.
STP STP Fundamentals
What is the primary purpose of Spanning Tree Protocol?