Allows a port running STP to go directly from blocking to forwarding mode.
This will bypass the 50 second timer (20 seconds max age, 15 seconds listening, 15 seconds learning).

sh spanning-tree interface fastEthernet 0/1
SW(config)#spanning-tree portfast ?
 bpdufilter Enable portfast bpdu filter on this switch
 bpduguard Enable portfast bpdu guard on this switch
 default Enable portfast by default on all access ports

SW(config-if)#spanning-tree portfast ?
 disable Disable portfast for this interface
 trunk Enable portfast on the interface even in trunk mode


Switch01 has two paths to the root (sw0) where one is FWD and one is BLCK.
With UplinkFast the port that could potentially reach the rootswitch is collectivly refered as an uplinkgroup (includes FWD and BLCK ports). If the FWD port goes down, the other ports will transition to FWD immediately (between 1-3 seconds).
Not recommended on core and distribuition switches making it “PortFast on the access layer”.
UplinkFast is enabled globally and for all VLANs on the switch.