Modify Preferred Forwarding Interface

B

The correct answer is B. The port priority.

In the context of Cisco's Spanning Tree Protocol (STP), the preferred forwarding interface is the interface that will be used to forward traffic on a particular VLAN. By default, the STP algorithm selects the interface with the lowest cost to the root bridge as the preferred forwarding interface. However, you can modify this behavior by adjusting the port priority for a specific interface.

The port priority is a value that is used to determine which port on a switch will be used as the preferred forwarding interface. The default port priority value is 128, and a lower value indicates a higher priority. To configure a specific interface as the preferred forwarding interface, you can lower its port priority value so that it becomes the preferred path for traffic.

For example, suppose you have two switches connected via multiple interfaces, and you want to ensure that all traffic for a particular VLAN is forwarded over a specific interface. In that case, you can lower the port priority value for that interface, making it the preferred forwarding interface for that VLAN.

To modify the port priority value for an interface, you can use the following command in Cisco IOS:

cCopy code
(config-if)# spanning-tree port-priority <value> 

Where <value> is a number between 0 and 240, in increments of 16. A lower value indicates a higher priority, and the default value is 128. Keep in mind that modifying the port priority value for an interface can impact the overall topology of your network, so it's essential to understand the implications of making such changes.