Configure the Port Priority

See STP Topology Example for the topology for this procedure. All switches are configured to be STP compatible using the spanning-tree compatibility stp command in Global Configuration mode. After the topology stabilizes, switch 1 is elected as root and all ports of all switches except port 2 and 3 (alternate, discarding) of switch 3 are in forwarding.

This example configures port 0/3 with a port priority of 32. Ports 1 and 2 of switch 2 become the alternate ports, and port 3 becomes the root port.

1. In switch 1, specify the interface for the port priority and configure the port priority for spanning tree.

   SEFOS# configure terminal
   SEFOS(config)# interface extreme-ethernet 0/3
   SEFOS(config-if)# spanning-tree port-priority 32
   SEFOS(config-if)# end

2. View the spanning tree properties of an interface.
   1. In Switch 1, type.

      SEFOS# show spanning-tree
       
      Root Id         Priority   32768
                      Address    00:01:02:03:04:01
                      Cost       0
                      Port       0 [0]
                      This bridge is the root
                      Max age 20 Sec, forward delay 15 Sec
                      Hello Time is 2 Sec
      MST00
      Spanning Tree  Protocol Enabled.
      MST00 is executing the mstp compatible Multiple Spanning Tree Protocol
      Bridge Id       Priority  32768
                      Address  00:01:02:03:04:01
                     Max age is 20 sec, forward delay is 15 sec
                      Hello Time is 2 sec                Dynamic Path Cost is Disabled                Dynamic Path Cost Lag-Speed Change is Disabled
      Name      Role         State        Cost     Prio   Type
      ----      ----         -----        ----     ----   ------
      Ex0/1     Designated   Forwarding   200000    128    SharedLan
      Ex0/2     Designated   Forwarding   200000    128    SharedLan
      Ex0/3     Designated   Forwarding   200000    32     SharedLan

   2. In Switch 2, type.

      SEFOS# show spanning-tree
       
      Root Id         Priority   32768
                      Address    00:01:02:03:04:01
                      Cost       200000
                      Port       2 [Ex0/2]
                     Max age 20 Sec, forward delay 15 Sec    
                      Hello Time is 2 Sec  
      MST00
      Spanning Tree  Protocol Enabled.
      MST00 is executing the mstp compatible Multiple Spanning Tree Protocol
      Bridge Id       Priority  32768 
                      Address  00:02:02:03:04:01
                     Max age is 20 sec, forward delay is 15 sec
                      Hello Time is 2 sec                Dynamic Path Cost is Disabled                Dynamic Path Cost Lag-Speed Change is Disabled
      Name      Role         State        Cost     Prio   Type
      ----      ----         -----        ----     ----   ------
      Ex0/1     Root       Forwarding   200000    128    SharedLan
      Ex0/2     Designated  Forwarding   200000    128    SharedLan

   3. In Switch 3, type.

      SEFOS# show spanning-tree
       
      Root Id         Priority   32768
                      Address    00:01:02:03:04:01
                      Cost       200000
                      Port       2 [Ex0/2]
                      Max age 20 Sec, forward delay 15 Sec              
                      Hello Time is 2 Sec
      MST00
      Spanning Tree  Protocol Enabled.
      MST00 is executing the mstp compatible Multiple Spanning Tree Protocol
      Bridge Id       Priority  32768 
                      Address  00:03:02:03:04:01
                     Max age is 20 sec, forward delay is 15 sec
                      Hello Time is 2 sec                Dynamic Path Cost is Disabled                Dynamic Path Cost Lag-Speed Change is Disabled
      Name      Role         State        Cost     Prio   Type
      ----      ----         -----        ----     ----   ------
      Ex0/1     Alternate    Discarding   200000    128    SharedLan
      Ex0/2     Alternate    Discarding   200000    128    SharedLan
      Ex0/3     Root         Forwarding   200000    128    SharedLan