D.3. Routers and Subnets

If every computer on the Internet had to know the location of every other computer on the Internet and how to get from here to there, the entire Internet would have come to a grinding halt long ago. Early on, it became apparent that some method was needed to filter and route packets to allow users to not only print to their network printers easily, but also to reach any other computer on the Internet without having to know a whole lot about how to get there. Enter subnets, routers, and gateways.

D.3.1. What Is a Subnet?

A subnet is simply a portion of the network that operates as a separate network, without regard to what happens outside and without affecting the rest of the network. A subnet is usually a separate physical “wire” that has only a single point of contact with other areas of the network, through a router or bridge—although even when two subnets share the same physical wire, they still require a router to connect to each other.