STP Configuration and Management 1 — Questions and Answers
Question 1: What STP parameter can be adjusted to influence which switch becomes the Root Bridge?
- Port Cost
- Bridge Priority (Correct answer)
- Forward Delay
- Hello Time
Correct answer: Bridge Priority
The Bridge Priority is a configurable value within a switch's Bridge ID, which is used to determine the Root Bridge. A lower bridge priority value increases the likelihood of a switch becoming the Root Bridge. Network administrators can manually adjust this value to influence the Root Bridge election and optimize network traffic flow according to their design.
Question 2: What is the effect of configuring PortFast on a switch port?
- It prevents the port from participating in STP
- It allows the port to transition immediately to the Forwarding state (Correct answer)
- It decreases the port’s bandwidth usage
- It increases the time the port spends in the Listening state
Correct answer: It allows the port to transition immediately to the Forwarding state
PortFast is an STP feature designed for access ports connected to end devices (like workstations or servers), not other switches. When enabled, PortFast allows the port to bypass the Listening and Learning states and immediately transition to the Forwarding state. This significantly reduces the time end devices wait to connect to the network, improving user experience.
Question 3: Which STP variant is designed to provide faster convergence compared to traditional STP?
- Multiple Spanning Tree Protocol (MSTP)
- Rapid Spanning Tree Protocol (RSTP) (Correct answer)
- Common Spanning Tree (CST)
- Per-VLAN Spanning Tree (PVST)
Correct answer: Rapid Spanning Tree Protocol (RSTP)
Rapid Spanning Tree Protocol (RSTP) is an evolution of traditional STP designed to provide much faster convergence times. It achieves this by introducing new port roles and states, and by actively negotiating port roles with neighboring switches. This allows for quicker recovery from link failures and topology changes, minimizing network downtime and improving network resilience.
Question 4: How can you verify the current STP configuration and status on a Cisco switch?
- Use the show ip interface command
- Use the show spanning-tree command (Correct answer)
- Use the show vlan command
- Use the show mac-address-table command
Correct answer: Use the show spanning-tree command
On Cisco switches, the `show spanning-tree` command is the primary tool for verifying the STP configuration and operational status. It displays information such as the Root Bridge, bridge priorities, port roles (Root, Designated, Blocking), port states (Forwarding, Learning, Blocking), and port costs for all VLANs. This command is essential for troubleshooting and monitoring STP in a network.
Question 5: What is the purpose of configuring a port’s cost in STP?
- To increase the speed of port transitions
- To influence the selection of the Root Bridge
- To determine the path preference and loop prevention (Correct answer)
- To control the frequency of BPDU transmissions
Correct answer: To determine the path preference and loop prevention
Port cost is an STP parameter that represents the 'cost' of sending data out of a specific port. Switches use port costs to calculate the shortest path to the Root Bridge and to determine which redundant links should be blocked to prevent loops. Lower cost paths are preferred, allowing administrators to influence traffic flow and ensure optimal network performance and redundancy.
STP Configuration and Management 1
What STP parameter can be adjusted to influence which switch becomes the Root Bridge?