How a router picks the next step
A router does not need to know what a packet’s message says. It reads the packet’s network address—the destination information attached to it—and compares that address with a routing table. The table lists possible next steps, called routes, for reaching different groups of addresses. The router sends the packet to the next router or network link that best matches the destination.
That next step is not always the whole journey. Each router makes its own decision when the packet arrives, so packets from one message can take different paths. The destination device uses information carried in the packets to put the message back together.
Why the route can change
Routing tables are updated as networks connect, disconnect, or become unavailable. A router can therefore send traffic along another workable path if a link fails. This is not necessarily a search for the physically shortest route: networks choose paths according to their connections and policies, and congestion can affect how quickly data travels.
At home, the router also bridges two different sides of the connection: the local network used by devices such as laptops and TVs, and the internet-facing connection supplied by a provider. Many home routers also translate between local device addresses and a shared public address. That lets several devices use one internet connection, while the routing function still decides where their packets go.
