BPDUGuard
I talked about this a bit earlier—if you turn on PortFast for a switch port, turning on BPDUGuard
is a really good idea. If a switch port that has PortFast enabled receives a BPDU on that
port, it will shut that port down and put it into an error-disabled state.
S1(config-if-range)#spanning-tree bpduguard ?
disable Disable BPDU guard for this interface
enable Enable BPDU guard for this interface
S1(config-if-range)#spanning-tree bpduguard enable