# 22 Fundamentals of IP Version 6

### IPv6 header

For example, all of the following are IPv6 addresses, each with 32 or fewer hex digits:
2345:1111:2222:3333:4444:5555:6666:AAAA
**IPv6** increases the address to **128 bits** in length.
**IPv4** uses a **32-bit** address

### The Historical Reasons for IPv6

### IPv6 routing

### IPv6 Routing Protocols

### IPv6 Addressing Formats and Conventions
■ How to write and interpret unabbreviated 32-digit IPv6 addresses
■ How to abbreviate IPv6 addresses and how to interpret abbreviated addresses
■ How to interpret the IPv6 prefix length mask
■ How to find the IPv6 prefix (subnet ID), based on an address and prefix length mask

**Representing Full (Unabbreviated) IPv6 Addresses**

#### Abbreviating and Expanding IPv6 Addresses

**Abbreviating IPv6 Addresses**
For example, consider the following IPv6 address. The bold digits represent digits in which the address could be abbreviated.
**FE00:0000:0000:0001:`0000:0000:0000`:0056**

Applying the first rule, you would look at all eight quartets independently. In each, remove all the leading 0s. Note that five of the quartets have four 0s, so for these, remove only three 0s, leaving the following value:
**FE00:0:0:1:0:0:0:56**
In this case, two instances exist where **``more than one quartet in a row has only a 0.``**
**FE00:0:0:1`::`56**

**Expanding Abbreviated IPv6 Addresses**

**Representing the Prefix Length of an Address**
IPv6 uses a mask concept, called the prefix length, similar to IPv4 subnet masks.
When writing an IPv6 address and prefix length in documentation, you can choose to leave a space before the /, or not, as shown in the next two examples.

Finally, note that the prefix length **is a number of bits**, so with IPv6, **the legal value range is from 0 through 128, inclusive.**

**Finding the IPv6 Prefix**

**prefix /64**

**prefix /56**