Most newer Cisco switches use RSTP by default. RSTP prevents frame looping out of the box and no additional configuration is necessary. To check whether a switch runs RSTP, the show spanning-tree command is used:
SW1#show spanning-tree VLAN0001 Spanning tree enabled protocol rstp Root ID Priority 32769 Address 0004.9A47.1039 This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32769 (priority 32768 sys-id-ext 1) Address 0004.9A47.1039 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 20 Interface Role Sts Cost Prio.Nbr Type ---------------- ---- --- --------- -------- -------------------------------- Fa0/3 Desg FWD 19 128.3 P2p Fa0/2 Desg FWD 19 128.2 P2p
If RSTP is not being used, the following command will enable it:
SW1(config)#spanning-tree mode rapid-pvst
Most other configuration options (electing root switch, selecting root and designated ports) are similar to the ones used in STP.
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