Due to the shortage of IPv4 addresses IPv6 has been developed. It is the successor protocol that will be used in parallel to IPv4 to drive the Internet’s underlying infrastructure. In this series of four blog posts I will give a general introduction to the most important aspects of IPv6 with a focus on the pen tester’s point of view. Be aware that this series is about the fundamentals and thereby does not cover all the dirty little details.

In part 1 we will cover IPv6 in general and how an IPv6 address look like.

IPv6 Overview

The easiest to spot change is that the IPv6 addresses are a lot longer than its IPv4 siblings. The additional bits increases the available address space and thereby allow us to address a lot more devices. Here are the numbers:

• IPv4 address: 32bit (4294967296 available IP addresses)
• IPv6 address: 128bit (340282366920938463463374607431768211456 available IP addresses – And yes, every single atom on the earth surface can be addressed with IPv6. You can even assign more than 100 addresses to each one – Reference)

Furthermore IPv6 has many great features built in like:

• Mobility (you always use the same IP address wherever you are)
• Security (IPsec is built in)
• It eliminates the need to use NAT
• …

Now let’s take a more close look at how an IPv6 address looks like:

How does an IPv6 address look like

Here is an IPv6 address in its full glory: fe80:0000:0000:0000:02aa:00ff:fe28:9c5a/64

As you can clearly see, IPv6 addresses are not as easy to write and remember as IPv4 addresses. They are composed of 8 sections each representing 16bits of the full 128bit address space written in hexadecimal notation. Furthermore it is compose of two parts: the network portion and the host portion. The network portion is defined using the CIDR notation (/64 in the above example) and is used for traffic routing. To make it a bit easier for us humans, there are three tricks that can be applied to make the address a little easier to handle:

1. The first thing you need to know is that is does not matter if you use lower case or capital letters. You can even mix case if you like to. That means that the following examples are valid addresses and all three represent the same host:

   Example 1: fe80:0000:0000:0000:02aa:00ff:fe28:9c5a
   Example 2: FE80:0000:0000:0000:02AA:00FF:FE28:9C5A
   Example 3: Fe80:0000:0000:0000:02Aa:00fF:fE28:9c5A
   

2. Secondly, leading zeros can be removed for each section. However be aware that if a section contains only zeros at least one has to remain. Again the following examples are valid addresses for the same host:

   Example 1: fe80:0000:0000:0000:02aa:00ff:fe28:9c5a
   Example 2: fe80:0:0:0:02aa:00ff:fe28:9c5a
   Example 3: fe80:0:0:0:2aa:ff:fe28:9c5a
   

3. 3) Finally, rule number three allows you to replace consecutive sections of zeros with ::. However be aware that this is allowed only once. While parsing the address the computer knows that IPv6 addresses always have to have eight sections and simply replaces the :: with the correct number of sections filled with zeros. The following examples illustrate the process:

   Example 1: fe80:0:0:0:2aa:ff:fe28:9c5a => fe80::2aa:ff:fe28:9c5a
   Example 1: 2000:0:0:0:111:ffdc:0:8f21 => 2000::111:ffdc:0:8f21
   

In this post we discussed some advantages of IPv6, how addresses look like and what tricks can be used to shorten them. In the next one we will take a closer look at the different addresse types and IPv6 Link Local addresses.