The All-New Switch Book: The Complete Guide to LAN Switching Technology, Second Edition

5.7. Configuring the Spanning Tree

Well-designed systems allow "power users" to custom-tailor a configuration to their specific needs, but provide defaults that are appropriate for the vast majority of situations.^[] If left to its default behavior, the STP will automatically select the Root Bridge, all Designated Bridges, and all Designated Ports according to the algorithm described in section 5.2.2.2. For many users, this is perfectly adequate; the catenet will properly resolve loops and provide full connectivity along the best available paths. However, the STP also incorporates a great deal of flexibility for the network administrator who, for example:

^[] The VMS operating system comes to mind as one of the great examples of this principle.

• Has a complex configuration of bridges, with many potential Designated Bridges for a given link

• Wants to carefully control the configuration and topology change behavior in anticipation of specific events (bridge failures, link failures, and so on)

• Knows that the default behavior will result in an undesirable configuration (for example, a known, numerically low Bridge Identifier is present on a bridge connected to a low-speed link at the edge of the catenet)

• Needs to configure a specific bridge as root, possibly as a requirement for a proprietary WAN load-sharing algorithm

• Wants to tune the performance and convergence of the protocol for specific needs

The STP allows the network administrator to adjust the STP parameters to achieve almost any ...