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

5.5. An Example of Loop Resolution

Rather than deal with all of the concepts in abstract and algorithmic terms, let's take a look at an example of a catenet with loops and see how the STP works to resolve the loops and achieve a tree topology.

You are watching a trained network professional. The stunts being performed entail a high degree of risk, require years of practice, and should not be attempted by amateurs or young children. Don't try this at home.

Before you go off and build a replica of the depicted catenet for use in your organization, be aware that the example is primarily designed to demonstrate STP behavior; as such, it includes a number of interesting boundary conditions and link configurations that rarely occur in most environments. That is, the example is not necessarily practical or useful for any normal purposes. Given that caveat, consider the configuration shown in Figure 5-17.

Figure 5.17. Example configuration

For simplicity, we assume that all of the Bridge and Port Priorities are left at their default values (or set to a common value, which amounts to the same thing). Each bridge is shown with a (simplified) numerical Bridge Identifier, each port with a Port Identifier, and each link with an associated cost.

Following the algorithm described ...