Which type of addressing is used at Layer 3?

• A. MAC addresses
• B. GUIDs
• C. Port numbers
• D. IP addresses

Answer: (D)

Layer 3, the Network Layer, handles routing and forwarding packets between networks, so the addressing used here must be scalable across multiple hops. IP addresses provide this logical, network-wide identification for devices, allowing routers to determine how to reach a destination across different networks. In TCP/IP networks, IP addresses come in IPv4 or IPv6 forms and enable hierarchical routing, which is essential for moving data through complex networks. Within a local network, a separate mechanism (like ARP) maps that IP address to a physical MAC address so the frame can actually be delivered to the next hop, but the addressing scheme at Layer 3 is IP. By contrast, MAC addresses operate at Layer 2 for local-link delivery, port numbers at Layer 4 identify specific applications, and GUIDs are software identifiers rather than network addresses.