In IP routing, how do routers determine where a packet needs to go?

In IP routing, how do routers determine where a packet needs to go?

• A. Routers look at the IP packet header and use the destination address field.
• B. Routers rely on the payload content to determine routing.
• C. Routers use the TCP port number to forward packets.
• D. Routers determine destination from DNS records.

Answer: (A)

The main idea is that routing decisions are based on the destination IP address found in the IP header. Routers look at that address and use their routing table to pick the best next hop toward that destination. The routing table is built from networks the router can reach, learned through static routes or dynamic routing protocols, and it often uses the longest-prefix match to choose the most specific route. If there’s no specific match, a default route is used. This decision is about the network layer only. The content inside the packet (the payload) or transport-layer details like TCP/UDP port numbers aren’t used for forwarding decisions by routers. DNS is involved earlier to translate a domain name into an IP address, but once the packet is on the network, routing relies solely on the destination IP address and the routing table.

The main idea is that routing decisions are based on the destination IP address found in the IP header. Routers look at that address and use their routing table to pick the best next hop toward that destination. The routing table is built from networks the router can reach, learned through static routes or dynamic routing protocols, and it often uses the longest-prefix match to choose the most specific route. If there’s no specific match, a default route is used.

This decision is about the network layer only. The content inside the packet (the payload) or transport-layer details like TCP/UDP port numbers aren’t used for forwarding decisions by routers. DNS is involved earlier to translate a domain name into an IP address, but once the packet is on the network, routing relies solely on the destination IP address and the routing table.