What is the operating mode and role of a backup port on a shared LAN...

blocking mode and provides an alternate path toward the designated bridge. Layer 2 switching behavior is driven by VLAN membership, MAC learning, trunk encapsulation, STP state, and EtherChannel negotiation. Cisco switches learn source MAC addresses on ingress, flood unknown unicasts within the same VLAN, and forward known unicasts only out the port associated with the destination MAC address. Trunk and EtherChannel questions must be solved on the logical interface and with the correct negotiation protocol: LACP uses active/passive, PAgP uses desirable/auto, and static mode uses on. STP and PortFast questions depend on whether the port is intended for an endpoint or part of the switched topology. The wrong choices usually apply the correct feature to the wrong port type or violate the required negotiation behavior. Cisco CCNA 200-301 v1.1 emphasizes these details because a single incorrect Layer 2 setting can create loops, VLAN leaks, or failed host connectivity. The selected answer matches Cisco switching operation.