What type of address is used only at the network layer for routing purposes?

• A. MAC address
• B. IP address
• C. Port number
• D. URL

Answer: (B)

Routing across networks relies on addresses at the network layer to direct packets toward their destination. That means IP addresses are used by routers to determine how to forward a packet from one network to another, with routers reading the destination IP to pick the next hop and the best path.

The MAC address operates at the data link layer and is used to deliver frames within a single local network segment; it isn’t used for routing between networks (frames are re-encapsulated with new link-layer addresses as they cross hops). Port numbers identify processes on a host at the transport layer, helping multiplex multiple applications but not guiding routing decisions across networks. URLs are application-layer identifiers that get resolved to IP addresses (via DNS, for example) but aren’t themselves the addresses routers use to route traffic.

So the address used specifically for routing purposes at the network layer is the IP address.