A frame with a broadcast destination address arriving at a switch: how is the frame forwarded?

• A. The switch broadcasts the frame only to devices on the same VLAN.
• B. The switch updates the MAC table and drops the frame.
• C. The switch forwards it out all ports except the ingress port.
• D. The switch discards the frame.

Answer: (C)

When a frame addressed to broadcast arrives at a switch, the switch cannot determine a single destination. To ensure all devices in that broadcast domain see it, the switch floods the frame out all ports that belong to the same VLAN as the port it came in on, except for the ingress port. This behavior also carries across trunk links, so devices on other switches in the same VLAN receive the frame as well. The switch does learn the source MAC from the frame, updating its MAC address table, but that learning doesn’t stop the flood. The frame is not discarded.