STP Uplinkfast

What are STP features to improve STP convergence process ?

1. Port-fast (already explained in the previous post )

2. UplinkFast

3. BackboneFast,

UplinkFast

Normally in STP topology, if root port on the local switch failed , let say RP on switch 3 failed due to some reason, during such situation, STP has to perform a recalculation to bring out other blocked port and so that port will transition into root port ,but this process will takes at least 30 sec , two forward-delay timer to bring port into forwarding mode, again this 30 sec delay is unavoidable in some environments, hence what UplinkFast does is it allow the blocked port to be held in Standby mode, so that when ever local switch detects there  is root port failure, UplinkFast feature immediately transitioned blocked port into forwarding state and  helps to inprove convergence process by bypassing those 30 sec forward  delay .

Note: if there are multiple blocked port , then UplinkFast will choose port having lowest root path cost n transitioned that port into forwarding state.

By default, UplinkFast is disabled and we can enable it globally for all Vlans on switch by below command .

Switch(config)# spanning-tree uplinkfast 

Actual function of UplinkFast is track the link to root bridge , hence UplinkFast is not supported on Root Bridge , it's only intended for down stream switches ,

Enabling UplinkFast feature automatically increase bridge priority to 49152