STP Configuration and Management 2 — Questions and Answers
Question 1: Which command sets a Cisco switch as the root bridge for VLAN 10 using the preferred method?
- spanning-tree vlan 10 priority 0
- spanning-tree vlan 10 root primary (Correct answer)
- spanning-tree vlan 10 root-bridge
- spanning-tree vlan 10 forward-time 0
Correct answer: spanning-tree vlan 10 root primary
The 'spanning-tree vlan 10 root primary' macro automatically sets the priority to 24576 (or lower if needed) to make the switch root.
Question 2: What is the default STP hello time on Cisco switches?
- 1 second
- 2 seconds (Correct answer)
- 4 seconds
- 10 seconds
Correct answer: 2 seconds
The default STP hello time is 2 seconds, which is the interval between configuration BPDUs sent by the root bridge.
Question 3: When configuring PVST+, what is the valid range for the spanning-tree port priority value?
- 0–255 in increments of 1
- 0–240 in increments of 16 (Correct answer)
- 0–255 in increments of 16
- 0–65535 in increments of 4096
Correct answer: 0–240 in increments of 16
Port priority in PVST+ ranges from 0 to 240 in increments of 16, with a default of 128.
Question 4: Which Cisco IOS command enables Rapid PVST+ globally on a switch?
- spanning-tree mode rapid-pvst (Correct answer)
- spanning-tree mode rstp
- spanning-tree rapid enable
- spanning-tree mode 802.1w
Correct answer: spanning-tree mode rapid-pvst
The command 'spanning-tree mode rapid-pvst' enables Rapid Per-VLAN Spanning Tree Plus on Cisco IOS switches.
Question 5: What happens to a port configured with 'spanning-tree bpduguard enable' when it receives a BPDU?
- The port transitions to blocking state
- The port is placed in err-disabled state (Correct answer)
- The port discards the BPDU and continues forwarding
- The port sends a topology change notification
Correct answer: The port is placed in err-disabled state
BPDU Guard immediately err-disables a port upon receiving a BPDU to protect against unauthorized switches.
Question 6: Which command verifies the STP root bridge and port roles on a Cisco switch for VLAN 1?
- show spanning-tree brief
- show spanning-tree vlan 1 (Correct answer)
- show spanning-tree root
- show spanning-tree summary
Correct answer: show spanning-tree vlan 1
The 'show spanning-tree vlan 1' command displays detailed STP information including root ID, local bridge ID, and all port roles for VLAN 1.
Question 7: What is the purpose of 'spanning-tree vlan 10 root secondary'?
- Sets priority to 0 to become backup root
- Sets priority to 28672 to become backup root if the primary fails (Correct answer)
- Configures the switch as a backup designated bridge
- Sets priority to 32768 as a secondary root backup
Correct answer: Sets priority to 28672 to become backup root if the primary fails
The 'root secondary' macro sets the bridge priority to 28672, making it the second-lowest priority to serve as backup root.
STP Configuration and Management 2
Which command sets a Cisco switch as the root bridge for VLAN 10 using the preferred method?