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 Example 12-3, where we change the spanning-tree port cost on SW3 from Figure 12-5. We will then examine what changes in Example 12-4.
Figure 12-5 Analysis of SW3’s Current Root Cost of 4 with Defaults
Back in Figure 12-4, with default settings, SW1 became root, and SW3 blocked on its Eth1/2 interface. A brief scan of the figure, based on the default STP cost of 2 for Ten Gigabit interfaces, shows that SW3 should have found a cost 2 path and a cost 4 path to reach the root, as shown in ...
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