Introduction to IPv6

What this chapter covers

This chapter builds the vocabulary you need before you configure anything on a router.

It explains what IPv6 changes compared with IPv4, how addresses are written and handed out, and how a host makes its own address. It then covers subnetting, the address types, and the special ranges that have a fixed meaning.

Everything later in the guide assumes you can read an IPv6 address on sight. Spend time here until the notation feels natural.

How the topics fit together

The chapter moves from the big picture, to a single address, to groups of addresses.

You start with the differences between the two protocol versions. That explains why the address is 128 bits and why broadcast and NAT are no longer central. You also see how address space is handed from the registries to ISPs and sites.

Next you learn the notation rules, such as dropping leading zeros and using :: once. Those rules are used on every page that follows.

Then you see how a host builds its address with SLAAC and EUI-64, and how a /48 or /56 is divided into /64 networks. Finally you learn to recognise link local, unique local, global, multicast and anycast addresses, together with the special addresses such as ::1, :: and the documentation prefix.

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 and example commands.
• What to remember for the exam: the facts to memorise.
• Common mistakes: the classic traps.
• Check yourself: three questions to test your understanding.

This chapter is mostly arithmetic and pattern recognition. Practise by expanding and shortening addresses on paper, and by converting a MAC address into an EUI-64 interface ID until you can do it without looking.

If you have a RouterOS device or a lab image, add a few addresses with /ipv6 address add and read them back with /ipv6 address print. Seeing the link local address appear on its own is a good way to remember the rule.