Addressing and Subnet Formats

What this chapter covers

Addressing is how every device on a network gets a unique identity so that data can find it.

This chapter looks at the two versions of the Internet Protocol. It explains the difference between private and public addresses, how an IPv4 address is split by a subnet mask, and how IPv6 addresses look and behave.

It is a chapter to practise with a pencil. Writing out masks, ranges and short forms helps the ideas stick.

How the topics fit together

The topics move from where addresses are used, to how IPv4 addresses are structured, to the newer IPv6 format.

The first page covers private and public addresses, the old address classes and NAT. It explains why most networks use private addresses inside.

The second page covers IPv4 subnetting. It shows how a mask and slash notation divide an address into network and host parts, and how that relates to broadcast domains.

The third page covers IPv6. It shows how to read and shorten the addresses, and how the types and prefixes compare with IPv4.

How to use these pages

Each topic page has the same shape, so you can skim for what you need.

• What it is: the idea in plain words.
• How it works: the mechanism, with diagrams, tables and worked examples.
• What to remember for the exam: the facts to memorise.
• Common mistakes: the classic traps.
• Check yourself: three questions to test your understanding.

Try the worked examples on paper before you read the answers. Use a subnet calculator afterwards to check your work.

If a topic feels hard, go back to the page on models in the first chapter. Knowing which layer an address belongs to makes the rest easier. The chapter after this one covers the cables and devices that carry these addresses.