When a router forwards a packet to the next hop, what happens to the MAC addresses?
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Correct answer: The router replaces the original source and destination MAC addresses with the sending router MAC address as the source and neighbor MAC address as the destination..
Why this is the answer
When a router forwards a packet, it operates at Layer 3 (Network Layer) for IP addressing and Layer 2 (Data Link Layer) for MAC addressing. Each hop across a network segment involves a new Layer 2 frame. The router decapsulates the incoming frame, examines the destination IP address, and determines the next hop. It then constructs a new Layer 2 frame for the outgoing interface. This new frame will have the MAC address of the router's outgoing interface as the source MAC address and the MAC address of the next-hop device (another router or the final destination host) as the destination MAC address. The original source and destination MAC addresses from the incoming frame are discarded because they are only relevant to the previous Layer 2 segment. The IP addresses (Layer 3) remain unchanged unless Network Address Translation (NAT) is involved.
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