An engineer is documenting how a Layer 2 switch builds and uses its MAC address table on a single VLAN with default settings. Which statements accurately describe the switch's behaviour as it learns addresses and forwards frames? Select THREE.
- AIt records the source MAC of each arriving frame against the port on which the frame was received. Correct
- BIt floods a unicast frame out every port in the VLAN except the ingress port when the destination MAC is unknown. Correct
- CIt populates the table using the destination MAC of each frame and the port towards which the frame is sent.
- DIt refreshes the ageing timer for an existing entry every time that source MAC sends another frame. Correct
- EIt consults the destination IP address to choose the egress port for a frame within the VLAN.
Why A is correct: MAC learning works on the source address of inbound frames, mapping that address to the ingress port so future traffic can be sent there.
Why B is correct: An unknown-unicast frame is flooded to all other ports in the VLAN so it can reach a host the table has not yet learned, while the ingress port is excluded.
Why C is wrong: This is tempting because forwarding uses the destination MAC, but learning is based on the source MAC and the ingress port, not the destination.
Why D is correct: Each frame from a known source resets the entry's ageing timer, so an active host stays in the table and only idle entries are removed.
Why E is wrong: This confuses Layer 3 routing with Layer 2 switching, since a switch forwards inside a VLAN using the destination MAC, not the IP address.