Configuring Spanning Tree STP/RSTP Configurations
Configuration Guide  
  217
Step 6 copy running-config startup-config
Save the settings in the configuration file.
This example shows how to enable spanning tree function, configure the spanning tree 
mode as RSTP and verify the configurations:
Switch#configure
Switch(config)#spanning tree mode rstp
Switch(config)#spanning-tree
Switch(config)#show spanning-tree active
Spanning tree is enabled
Spanning-tree’s mode: RSTP (802.1w Rapid Spanning Tree Protocol)
Latest topology change time: 2006-01-02 10:04:02
Root Bridge
Priority      : 32768
Address       : 00-0a-eb-13-12-ba
Local bridge is the root bridge
Designated Bridge
Priority      : 32768
Address       : 00-0a-eb-13-12-ba
Local Bridge
Priority      : 32768
Address       : 00-0a-eb-13-12-ba
Interface    State       Prio      Ext-Cost      Int-Cost      Edge     P2p            Mode     Role      Status
---------     --------     ----        --------         --------         ----        ---------      -----        -----       -------
Gi1/0/16    Enable   128       200000      200000         No        Yes(auto)    Rstp        Desg     Fwd
Gi1/0/18    Enable   128       200000      200000         No        Yes(auto)    Rstp        Desg     Fwd
Gi1/0/20    Enable   128       200000      200000        No        Yes(auto)    Rstp        Desg     Fwd
Switch(config)#end
Switch#copy running-config startup-config