Networking: 10,000 foot View IPV6 Part 3

Published on November 15, 2021 at 7:00 am by LEW


In this post we will take what we studied in part 1 and part 2 and apply them to deconstructing several IPV6 address examples. As noted an adapter can have more than one IPV6 address, so we will be looking at several different types of IPV6 addresses. While they are all IPV6 addresses, they serve different purposes.

The Default Route “::/0”

This address is is in effect when no other route is available. It generally points to a network service routing device. The IPV6 expanded address looks like this.

0000:0000:0000:0000:0000:0000:0000:0000 /0

As a general home user, unless you are deeply involved in managing your LAN, you will probably never use this one.

The No Address Address “::/128”

Initially your network adapter has no IP address. This is expresses as “::/128”. If we use the rules from the previous posts, and expand this out then we get the following.

0000:0000:0000:0000:0000:0000:0000:0000 /128

Yes this is a real thing, and it is the initial IPV6 address of your network adapter before it initializes its own IPV6 address. It is also referred to as unspecified. You will probably never have to directly deal with this address either.

The Loop Back Address “::1/128”

The “::1/128” address is used when you want to test your network adapter by pinging yourself. It can also be used when programs on the same computer send data to each other. This address expands to the following.

0000:0000:0000:0000:0000:0000:0000:0001 /128

This is one you might use if you need to test the functionality of your network adapter separate from the rest of the network.

Global Unicast Address (GUA)

A Global Unicast Address (GUA) is a publicly routable IPV6 address. If your device is connected to the internet using IPV6, you will have a GUA. Your GUA will consist of the IANA prefix (bits 1 though 3), Regional Registry (bits 4 through 23), ISP Prefix (bits 24 through 32), Site Prefix (bits 33 through 48), Subnet Mask (bits 49 through 64), and finally your Interface Address. For a GUA, the only part that you can control is the Interface Address.

Below is a sample address. The first four sets of numbers are determined for you, and you will receive them form your ISP.

2607:fb91:140a:2a30:cc2f:c3bf:d4fa:42a2 /64

The last four sets of numbers are determined by your device in one of three ways.

  1. Manual, you assign the interface address yourself.
  2. EUI-64 which involves using your network adapter MAC address to derive the interface address.
  3. Random uses an algorithm to determine the interface address based on the devices clock.

Another example of this type of address is a google DNS server address.



Note we have not specified a slash ending. This is someone else address, and it is what it is. It would technically be /128 as we have no control over it.

Link Local Unicast Address fe80::/10

If your network adapter is functional, it will have a link-local address, which is also unicast. This type of address should not be routed across the public internet. This type of address always starts with fe80. From our above example, we could derive a link local address.

fe80:0000:0000:0000:cc2f:c3bf:d4fa:42a2 /10

Unique Local Unicast Address (ULA) fd00:: /8

The Unique Local Address (ULA) is a non public routable private network address. It always starts with fd. This is the type of address scheme a company might set up for their internal network, it the desire is to keep more control over device IPV6 addresses.

Multicast and AnyCast Addresses

We have not gotten into the multicast or anycast types of IPV6 addresses for IPV6. Unless you have specific needs you will not be dealing with these two groups normally.


It is the hope that this short introduction to IPV6 will help you understand basic usage. I have tried to avoid getting to far into  the technical weeds.  I plan to do a deep dive, going down to the bit level in latter posts.

Networking: 10,000 foot View IPV6 Part 1

Networking: 10,000 foot View IPV6 Part 2

Networking: 1o,000 foot View IPV6 Part 3

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