IPv6 Basics Part 2 - Unicast Addressing

IPv6 Unicast Addressing

RFC4291 details the IPv6 addressing architecture. In terms of unicast addresses, the addresses you really need to be aware of are.

Loopback Address

In IPv4 this is of course. In IPv6 the loopback address is simply ::1

Link Local Addresses

Similar to IPv4's APIPA addresses, a link local address is scoped soley to your local L2 segment. The most obvious difference compared to IPv4 though is that Link Local Addresses are mandatory in IPv6. (So even if you statically assign IPv6 addresses to your hosts, they will keep their Link Local Addresses too.)
Link local addresses have addresses in the range fe80::/64

Global Unicast Addresses

Essentially, this is the public IPv6 address space and is numbered 2000::/3
You can of course get Provider Allocated (PA) IPv6 space as you could with IPv4, but an option that is now available to a wider range of organisations, is to go to your regional internet registry and get your own Provider Independant (PI) IPv6 space.

Unique Local Addresses

RFC4193 defines Unique Local Addresses (ULAs), the IPv6 equivalent of IPv4's private addresses. Currently, ULAs should be allocated from the range fd00::/8

Although ULA's aren't routable across the internet, the recommendation is to randomly choose your prefixes from the range to try and keep the addresses unique globally. (Thus reducing the liklihood of needing to renumber the network in a merger scenario) There is a ULA prefix generator here to this end.

Whether or not you should use ULAs should be carefully considered. In IPv4, the default design in most cases, is to hide private address ranges behind behind edge NAT, however, this is borne out of necessity rather than desirability in most cases.

Ivan Pepelnjak has written a useful blog that discusses if/when you might need/want to use ULAs. (To be fair he's written useful blogs about pretty much every aspect of networking you could imagine)

IPv6 Basics Part 1 - Address Format & Types

IPv6 Basics Part 2 - Unicast Addressing

IPv6 Basics Part 3 - Protocol Differences

IPv6 Basics Part 4 - Multicast

IPv6 Basics Part 5 - Planning an IPv6 Network