routing-basics

A packet has destination IP — which next hop should router pick?

Per Wikipedia: “Routing chooses next hop using tables built from protocols that exchange reachability and compute shortest path.”

Routing is GPS for packets — each intersection consults map and forwards toward destination.

1. Router learns routes via protocol
2. Builds forwarding table
3. Looks up destination on arrival
4. Forwards via best next hop
5. Updates on topology change

• Decentralized — each router decides
• Convergence time after failure
• Longest prefix match for IP
• May cause loops transiently

• Built from: Store-and-Forward — routing decides where to forward
• Related: Packet Switching — routing enables switching
• Related: Datagram Network — datagrams need routing
• Related: Network Topology — topology informs routes

• Static routes stale after link fail
• Loop without TTL — packet circles forever