STP Troubleshooting STP 2 — Questions and Answers
Question 1: How do you configure STP priority for load balancing across VLANs?
- Set different root bridges for different VLANs using per-VLAN priority values (Correct answer)
- All VLANs must use the same root
- Load balancing is not possible with STP
- Use IP routing instead
Correct answer: Set different root bridges for different VLANs using per-VLAN priority values
By making different switches the root bridge for different VLANs, traffic can be distributed across redundant links.
Question 2: What is the TCN BPDU?
- Topology Change Notification sent by a switch when it detects a port state change (Correct answer)
- A type of network attack
- A timer configuration
- A management message
Correct answer: Topology Change Notification sent by a switch when it detects a port state change
TCN BPDUs notify the root bridge of topology changes so the network can update its forwarding tables.
Question 3: How does STP interact with EtherChannel?
- STP treats an EtherChannel as a single logical link, preventing it from blocking individual member ports (Correct answer)
- STP blocks all EtherChannel ports
- EtherChannel disables STP
- They are incompatible
Correct answer: STP treats an EtherChannel as a single logical link, preventing it from blocking individual member ports
EtherChannel bundles physical links into one logical link, so STP sees a single high-bandwidth connection rather than redundant links.
Question 4: What is the recommended STP configuration for access layer ports?
- Enable PortFast and BPDU guard on all access ports connected to end devices (Correct answer)
- Leave default settings
- Disable STP on access ports
- Set all access ports as root ports
Correct answer: Enable PortFast and BPDU guard on all access ports connected to end devices
PortFast provides immediate connectivity while BPDU guard protects against unauthorized switches being connected.
Question 5: What debugging tools are available for STP issues?
- debug spanning-tree events, show spanning-tree detail, show spanning-tree interface (Correct answer)
- Only ping and traceroute
- Only log files
- No debugging tools exist for STP
Correct answer: debug spanning-tree events, show spanning-tree detail, show spanning-tree interface
Multiple show and debug commands provide visibility into STP operations, state changes, and BPDU processing.
Question 6: What is the best practice for STP timer configuration?
- Use default timers unless there is a specific justified reason to change them (Correct answer)
- Always increase all timers
- Set all timers to minimum
- Timer changes are required for all networks
Correct answer: Use default timers unless there is a specific justified reason to change them
Default STP timers are carefully calculated based on worst-case scenarios and should generally not be modified.
STP Troubleshooting STP 2
How do you configure STP priority for load balancing across VLANs?