Global Unicast Addresses

I started reading about IPv6 because well it's about time and given I run it at home I probably should so I started reading the Cisco IPv6 Fundamentals book. And I guess let's start from the the basics of IPv6 addresses. 

We all know or of you're a network engineer or anyone who's been around th block in IT the good old trusty IPv4 addresses. Those neat little 32 bit binary easy to remember addresses. 4 octets and a number from 0-255 in each one. Well IPv6 throws that out the window with its 128 bit hexadecimal addresses. So now we not only have 0-9 but a - f as well in our addresses. IPv6 does break down this massive long 128 bit address into chunks of 16 bits per hextet. That makes 8 hextets in total to make up our IPv6 address.

Lile IPv4, IPv6 Global Addresses also break down the address into a network and a host portion.... Kind of. While it's not called the same thing, the concept is there. Essentially it was decided to have a basic rule of 3-1-4. This rule relates to the number of hextets belonging to the Network/subnet/host portions. The first 3 hextets are the Network range similar to IPv4. It's was originally recommended that each RIR will allocate IPv6 addresses in a minimum of a /48to everyone including home users but this was since revised. ISPs will get a /32 but can request up to a /24 while end sites should get at least a"/48 but can also request larger. A /48 will still give us as an end user 16 subnet bits meaning we have 65536 subnets that we can use in our home or office network. And finally, the last 4 hextets are the host ranges. The reason for 4 hextets being used as the host range comes down to address assignment.

Due to the extremely large number and size of an IPv6 address, you wouldn't really go around statically assigning them. Hell most people wouldn't even use a dhcp server for IPv6. Instead IPv6 addresses are usually configure dynamically via SLAAC or stateless address autoconfiguration. SLAAC will be discussed later (Chapter 4 of the book) but for now know that IPv6 uses the device MAC address to come up with a unique address and will also invert the 7th bit and add fffe to the middle of the MAC address thus producing a 64bit hexadecimal address.