Networking All-in-One For Dummies, 7th Edition

Chapter 4

Routing

IN THIS CHAPTER

Examining the basic operation of a router

Considering different types of routers

Looking at the routing table

Examining how packets flow through a router

In the simplest terms, a router is a device that works at layer 3 of the OSI Reference Model. Layer 3 is the network layer, which means that layer 3 is responsible for exchanging information between distinct networks. And that’s exactly the function of a router: Connecting two or more networks so that packets can flow freely between them.

Routing is the general term that describes what routers do. In short, when a router receives a packet from one network that is destined for a device on another network, the router determines the best way to get the packet to its destination.

In a way, routers are the post offices of the Internet. When you drop a letter into a public mailbox, a mail carrier collects the mail and delivers it to a nearby post office. There, the mail is sorted and sent off to a regional post office, where the mail is sorted again and maybe sent off to yet another regional post office, ...