Configuring STP Port Costs

Changing the STP port costs requires a simple interface subcommand: spanning-tree [vlan x] cost x. To show how it works, consider the following example, which changes what happens in the network shown in Figure 2-4.

Back in Figure 2-4, with default settings, SW1 became root, and SW3 blocked on its G0/2 interface. A brief scan of the figure, based on the default STP cost of 4 for Gigabit interfaces, shows that SW3 should have found a cost 4 path and a cost 8 path to reach the root, as shown in Figure 2-5.

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Figure 2-5 Analysis of SW3’s Current Root Cost of 4 with Defaults

To show the effects of changing the port cost, ...

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