Networks

Networks come first because they are something you already use every day. You type an address into the browser and a page comes back. Knowing what is inside that round trip shows you where the code you have been writing actually stands.

There are four big things here: how you point at the other side (IP addresses and port numbers), what conventions you talk by (protocols such as HTTP, DNS, TCP and UDP), how you investigate when it will not connect (ping, arp and friends), and what is exchanged in a single round trip (the request and the response).

Where this chapter pays off most is in reading errors. When "cannot connect to the server" comes up, whether the name could not be looked up (DNS), the route is not open (IP) or the counter at the far end is closed (a port) leads to completely different work. Thinking in layers saves you the hours spent poking at settings at random.

There is a lot to learn, but hardly any hard reasoning. It is a collection of conventions, so the knack is to keep them filed by which situation they belong to. The idea of layers is the tool for that.

The exercises are past questions from the Fundamental Information Technology Engineer Examination, as they stand. Exam questions are built with choices aimed at the places people get wrong, so the choice you hesitated over is your own gap. The explanation after the answer says why the other three are wrong as well, so do read that part.