Question

An access switch port configured with spanning-tree portfast and spanning-tree bpduguard enable connects to a user workstation. A junior technician plugs an unmanaged consumer switch into that wall jack, and moments later the port goes into an err-disabled state and the user loses connectivity. What caused the port to shut down?

Accepted Answer

The port received a BPDU, and BPDU Guard err-disabled the interface

Answer

PortFast detected a loop and transitioned the port through the listening and learning states

Answer

Root Guard placed the port in a root-inconsistent state after receiving a superior BPDU

Answer

A native VLAN mismatch triggered the interface to err-disable