STP Configuration and Verification

Configuring and verifying Spanning Tree Protocol (STP) involves several steps. Here are the basic steps for configuring and verifying STP:

Enable STP: STP is typically enabled by default on switches. However, you should verify that STP is enabled on each switch in the network.

Configure the root bridge: In a STP network, one switch must be designated as the root bridge. You can manually configure the root bridge or allow the switches to elect a root bridge based on the lowest bridge ID. The bridge ID is a combination of the priority and the MAC address of the switch.

Configure bridge priorities: Each switch in the network has a priority value ranging from 0 to 65,535. The default priority is 32,768. To influence the root bridge selection process, you can adjust the priority of a switch by configuring a lower or higher priority value.

Configure port settings: You can configure port settings, such as port cost and port priority, to influence which ports are designated as root ports, designated ports, and blocked ports.

Verify the STP configuration: You can verify the STP configuration by checking the STP status, the root bridge ID, the root port, and the designated ports. You can also use commands such as “show spanning-tree” or “show spanning-tree vlan” to view the STP information.

Test the STP configuration: You should test the STP configuration by simulating link failures and verifying that the network converges properly. To summarize, configuring and verifying STP involves enabling STP, configuring the root bridge, configuring bridge priorities and port settings, verifying the STP configuration, and testing the STP configuration. By following these steps, you can ensure that STP is properly configured and operating in your network.

Cisco switches use STP (IEEE 802.1d) by default. You can buy some switches and connect them with Ethernet cables in a redundant topology, and STP will ensure that no loops exist. And you never even have to think about changing any settings!

Although STP works without any configuration, you should understand how STP works, understand how to interpret the STP-related show commands, and know how to tune STP by configuring various parameters. For example, by default, all switches use the same priority, so the switch with the lowest burned-in MAC address becomes the root. Instead, a switch can be configured with a lower priority, so the engineer always knows which switch is root, assuming that that switch is up and running.