UplinkFast is a Cisco specific feature that improves the convergence time of the How to enable the Spanning Tree Protocol debugs in Catalyst 6000/6500 Switches that run the Cisco IOS system software in the event of the failure of an uplink. The UplinkFast feature is supported on Cisco Catalyst 4500/4000, 5500/5000, and 6500/6000 series switches running CatOS. This feature is also supported on Catalyst 4500/4000 and 6500/6000 switches that run Cisco IOS® System Software and 2900 XL/3500 XL, 2950, 3550, 3560 and 3750 series switches. The UplinkFast feature is designed to run in a switched environment when the switch has at least one alternate/backup root port (port in blocking state), that is why Cisco recommends that UplinkFast be enabled only for switches with blocked ports, typically at the access-layer.
Note: Do not use on switches without the implied topology knowledge of a alternative/backup root link typically to distribution and core switches in Cisco multilayer design.