Routing

How a packet crosses the world.

Hop by hop

No device knows the whole path. Each router reads the destination, consults its table and forwards the packet one step closer, repeating until it arrives.

traceroute shows the hops and where the delay appears.
Packets in one conversation can take different routes and still arrive in order thanks to TCP.

Switches and routers

A switch moves frames between devices on the same network using MAC addresses. A router joins different networks and works with IP addresses.