Which command enables BPDU Guard on all Portfast-enabled interfaces?

The command that enables BPDU Guard on all Portfast-enabled interfaces is designed to ensure that any interface configured for Portfast will have BPDU Guard activated automatically. This is important in a network because BPDU Guard helps prevent loops by disabling a port if it receives a Bridge Protocol Data Unit (BPDU), which indicates the presence of switches that could create a loop.

By using the command "spanning-tree portfast bpduguard default," you are instructing the switch to apply BPDU Guard to all interfaces that are configured for Portfast. Given that Portfast is typically used on edge ports connected to end devices rather than switches, enabling BPDU Guard helps protect the network from potential topology changes caused by accidental switch connections.

In contrast, the other choices have various limitations. For instance, "spanning-tree portfast bpduguard enable" applies BPDU Guard individually to each Portfast-enabled interface rather than defaulting it system-wide. The command "spanning-tree bpduguard default" activates BPDU Guard for all interfaces but does not specifically limit it to only Portfast-enabled interfaces. Lastly, "spanning-tree bpduguard all" is not an available command in Cisco IOS. Understanding these nuances highlights the importance of using the correct command