(Optional) Configuring Port Priority If a loop occurs, the MSTP uses the port priority when selecting an interface to put into the forwarding state. You can assign higher priority values (lower numerical values) to interfaces that you want selected first and lower priority values (higher numerical values) that you want selected last. If all interfaces have the same priority value, the MSTP puts the interface with the lowest interface number in the forwarding state and blocks the other interfaces.
Note If the device is a member of a switch stack, you must use the spanning-tree mst [ instance-id ] cost cost interface configuration command instead of the spanning-tree mst [ instance-id ] port-priority priority interface configuration command to select a port to put in the forwarding state. Assign lower cost values to ports that you want selected first and higher cost values to ports that you want selected last. To configure port priority, perform this procedure: Before you begin • An MST must be specified and enabled on the device. • You must also know the specified MST instance ID and the interface used.
Procedure Configuring Multiple Spanning-Tree Protocol (Optional) Configuring Port Priority Command or Action Purpose Step 2 configure terminal Example: Device# configure terminal Enters global configuration mode. Step 3 spanning-tree mst instance-id root secondary Example: Device(config)# spanning-tree mst 0 root secondary Configures a devices as the secondary root device. For instance-id, you can specify a single instance, a range of instances separated by a hyphen, or a series of instances separated by a comma. The range is 0 to 4094. Step 4 end Example: Device(config)# end Returns to privileged EXEC mode. Command or Action Purpose Step 1 enable Example:
Device> enable Enables privileged EXEC mode. Enter your password if prompted. Configuring Multiple Spanning-Tree Protocol 19