How IP Routing Works
When you send data across the internet, it doesn't travel in a straight line from your computer to the destination. Instead, it hops through multiple routers, each making independent decisions about where to send the packet next.
Hop-by-Hop Decisions
Think of routing like asking for directions at each intersection. You don't get a complete map from start to finish. Instead, at each point, someone says "go that way" based on where you're trying to reach.
Each router along the path:
- Receives an incoming packet
- Looks at the destination IP address
- Consults its routing table to decide the best next hop
- Forwards the packet toward that next router
No single router knows the entire path — each just knows the best direction to send packets for various destinations.
Routing Tables
A routing table is like a simplified map that says "for addresses in this range, send packets through that interface." Routers build and update these tables automatically using routing protocols, sharing information with neighboring routers about what destinations they can reach.
This distributed approach makes the internet resilient. If one path becomes congested or fails, routers can adapt and send packets through alternative routes.
Troubleshooting With ICMP
ICMP (Internet Control Message Protocol) helps diagnose routing problems. The most common ICMP tool is ping, which sends a simple "are you there?" message to a destination and measures the response time.
Another tool, traceroute, shows each hop along the path to a destination, helping identify where problems occur.
Why This Matters
Understanding routing helps you:
- Grasp why internet paths aren't always direct
- Interpret network diagnostic tools
- Understand why latency varies
- Appreciate the internet's resilient design