The show spanning-tree mst interface interface-id privileged EXEC command displays information only if the port is in a link-up operative state. Otherwise, you can use the show running-config interface privileged EXEC command to confirm the configuration. (Optional) Configuring Path Cost The MSTP path cost default value is derived from the media speed of an interface. If a loop occurs, the MSTP uses cost when selecting an interface to put in the forwarding state. You can assign lower cost values to interfaces that you want selected first and higher cost values that you want selected last.
If all interfaces have the same cost value, the MSTP puts the interface with the lowest interface number in the forwarding state and blocks the other interfaces. To configure path cost, 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. Configuring Multiple Spanning-Tree Protocol (Optional) Configuring Path Cost Command or Action Purpose Step 2 configure terminal Example: Device# configure terminal Enters global configuration mode. Step 3 interface interface-id Example:
Device(config)# interface gigabitethernet 1/0/1 Specifies an interface to configure, and enters interface configuration mode. Step 4 spanning-tree mst instance-id port-priority priority Example: Device(config-if)# spanning-tree mst 0 port-priority 64 Configures port priority. • 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. • For priority, the range is 0 to 240 in increments of 16. The default is 128. The lower the number, the higher the priority. The priority values are 0, 16, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, 224, and 240.
All other values are rejected. Step 5 end Example: Device(config-if)# end Returns to privileged EXEC mode. Configuring Multiple Spanning-Tree Protocol 20