From the CCNP SWITCH Book:
"The UplinkFast feature on Catalyst switches enables leaf-node switches or switches at the ends of the spanning-tree branches to have a functioning root port while keeping one or more redundant or potential root ports in Blocking mode. When the primary root port uplink fails, another blocked uplink immediately can be brought up for use.
UplinkFast also makes some modifications to the local switch to ensure that it does not become the root bridge and that the switch is not used as a transit switch to get to the root bridge. In other words, the goal is to keep UplinkFast limited to leaf-node switches that are farthest from the root."
I don't get the point why the Uplinkfast should be enabled only on leaf-node switches. Can you give me an example of a transit switch where putting the port that receives suboptimal BPDUs into FW state, immediately after the failure of the link connected to the Root port, could bring to a loop?
Thanks in advance for help.