What does a router use to determine the path to send packets?

• A. IP address
• B. MAC address
• C. Domain name
• D. Port number

Answer: (A)

Routing decisions are made using the destination IP address. A router operates at the network layer and reads the IP header to determine which next hop and exit interface will best forward the packet toward its destination, consulting its routing table to pick the path. MAC addresses are used only for delivering frames on the local network segment, and the router may use ARP to learn the MAC of the next hop on that local link, but the actual path between networks is driven by IP routing. Domain names are resolved to IPs by DNS, but a router makes forwarding decisions based on the IP address, not the domain name. Port numbers belong to the transport layer and identify applications, not routing paths.