How does a router decide where each packet goes?
No router on the internet knows the whole route your data will take. Each one only knows the next hop.
▶ Start the storyA router reads the address on each packet and passes it to the next router that gets it closer. That is all. When a packet arrives, the router looks at the network address in its , checks its routing table, and sends the packet on to the next network on its journey. A packet is forwarded from one router to another until it reaches its destination.
No single router needs to know the whole path. A routing table holds network and next-hop pairs: for each destination, which neighbouring router is the best way to go. Think of a distribution map in package delivery, where each depot only knows which truck to load a parcel onto next. If the tables are consistent, simply relaying a packet to its is enough to deliver data anywhere.
Step 1: Packet arrives
On one of the router's lines
Step 2: Read the address
The destination in the
Step 3: Check the table
Find the
Step 4: Forward it
To the next router on the journey
A router does not keep a line for every device in the world. Because addresses are structured, a single routing table entry can stand for a whole group of devices. And the tables are not typed in by hand. Large networks change too quickly for that, so routers build their tables automatically with , which lets the network steer around failures and blockages. Dynamic routing dominates the internet.
The most familiar router is the box at home that links your computers to the internet. The first true IP router, however, was built by Ginny Travers at BBN in 1975 to 1976, and by the end of 1976 three of them were running on the experimental internet.
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Recap
Each router only needs to know the next hop for a destination, and routing protocols keep those tables up to date automatically.
💡 A trick to remember it · Routers play pass-the-parcel: nobody holds the map of the whole trip, each one just knows who to hand it to next.
Surprising fact · The first true IP router was built by Ginny Travers at BBN in 1975 to 1976, and three were running by the end of 1976.
Connects to
- 🏷️ How does every device on the internet get an address?
- 🧭 How did one maintenance command take Facebook off the internet for hours?
- 🕸️ What do your friendships, molecules and road maps have in common?
- 📦 How does the internet deliver your data without ever giving you a line of your own?
- 💬 What was the first message ever sent over the internet's ancestor?
Sources (3)
No source, no claim. Every fact in this lesson (14 claims) cites at least one of these.