What is the STP Port Fast (Portfast) feature, and what is the safety mechanism that prevents misuse on switch-to-switch links?

• A.PortFast should be configured on all switch ports including trunk links to speed up network convergence.
• B.PortFast causes an access port to transition immediately from Blocking to Forwarding, skipping Listening and Learning states (saves ~30 seconds). It is safe only on ports connected to end devices (PCs, servers, printers) because they cannot create switching loops. The safety mechanism is BPDU Guard: when enabled with PortFast, if the port receives a BPDU (which only a switch would send), the port is immediately err-disabled (shutdown), preventing a connected switch from creating a loop.
• C.PortFast disables STP entirely on the port, preventing any future STP participation.