Which command is used to configure the STP cost of an interface?

The command to configure the Spanning Tree Protocol (STP) cost for an interface is structured as "spanning-tree vlan vlan-id cost cost." This command allows you to explicitly define the cost associated with a particular VLAN on a specific interface. The STP cost is a crucial parameter because it influences the path selection process for the spanning tree algorithm.

In STP, the switch with the lowest accumulated cost to the root bridge is preferred, meaning that by adjusting the cost on specific interfaces, you can manipulate the topology. This is essential for network administrators aiming to control traffic flow or optimize redundant paths within a network.

Other commands provided in the choices serve different purposes. For instance, configuring port priority affects the selection of the designated port but does not set the cost. The commands related to “root primary” and “root secondary” pertain to manipulating the root bridge election process and are not directly related to setting an interface's cost. Understanding these distinctions helps in effectively managing STP configurations.