The Primary Effect of the Spanning-Tree Portfast Command

D

The primary effect of the spanning-tree portfast command is to immediately transition a port from the blocking or listening state to the forwarding state, bypassing the usual spanning-tree protocol (STP) learning and forwarding delay. This command is typically used on access ports that connect to end devices, such as desktops, printers, or servers, where there is no risk of creating a loop in the network.

Here is a more detailed explanation of each answer:

A. It immediately enables the port in the listening state. This statement is incorrect. The portfast command bypasses the listening state and immediately enables the port in the forwarding state.

B. It immediately puts the port into the forwarding state when the switch is reloaded. This statement is partially correct. The portfast command does immediately put the port into the forwarding state, but it is not dependent on the switch being reloaded. Portfast can be configured on a port at any time, and the port will immediately transition to the forwarding state.

C. It enables BPDU messages. This statement is incorrect. The portfast command does not enable or disable BPDU messages. BPDU messages are used by STP to detect loops in the network and ensure a loop-free topology. When portfast is enabled on a port, the switch does not send or receive BPDU messages on that port, as it assumes that the port is connected to an end device and not to another switch.

D. It minimizes spanning-tree convergence time. This statement is correct. The portfast command can help to minimize the time it takes for STP to converge after a topology change. Without portfast, a port must go through the listening and learning states before transitioning to the forwarding state, which can take up to 50 seconds. With portfast, the port immediately transitions to the forwarding state, reducing the convergence time.