ITPEC FE Morning October 2023 Question 31

It forwards a frame only to the port where the destination MAC address is — a layer 2 switch learns which MAC address sits on which port.

The switch records the source MAC address of each frame it receives against the port it arrived on, building a MAC address table. When a frame arrives, it looks up the destination MAC address and sends the frame out of that one port. Only when the address is not in the table yet, or the frame is a broadcast, does it flood all ports.

Answer (c)

Why not others:

• •(a) — fragmentation happens at the network layer, in a router (layer 3); a layer 2 switch does not look inside the IP packet
• •(b) — dynamic IP address allocation is the job of a DHCP server
• •(d) — sending every frame to all ports is what a repeater hub does, which is exactly what a switch avoids

Key rule: A repeater hub copies to all ports, a switch forwards by MAC address to one port, and a router forwards by IP address between networks.

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