Another search term I am seeing is "169.254.0.0/16 ipv6 equivalent". In IPv4, the 169.254.0.0/16 range is what you get if nobody tells your computer what IP address it should have. Many printers and other network devices will pick one of these addresses if not told otherwise, so if you unbox a few new PCs and a printer and hook them up to a switch or hub, they should be able to find and talk to each other using these zero-configuration or autoconfiguration addresses.

A more generic name for this is link-local addressing. These addresses only speak to other devices on the same switch or LAN that have also autoconfigured themselves, but they cannot speak across routers to the rest of the networked world. IPv6 devices always create a link-local address that will only speak to other devices on the same switch or LAN, whether or not another address is assigned. IPv6 link-local addresses are in the fe80:/10 prefix, meaning they will begin with fe8, fe9, fea or feb. Let's take a look:

Windows IP Configuration

Ethernet adapter Local Area Connection:

   Connection-specific DNS Suffix  . : ad.itkia.com
   IPv6 Address. . . . . . . . . . . : 2001:db8:192:0:6470:6fb9:76c7:aa85
   Link-local IPv6 Address . . . . . : fe80::6470:6fb9:76c7:aa85%11
   IPv4 Address. . . . . . . . . . . : 192.168.1.56
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : fe80::214:d1ff:fe1a:a533%11
                                       192.168.1.1

I highlighted in red the link-local addresses in the "ipconfig" output. Note that the gateway is a link-local address instead of the router's public address. The link-local address for my machine is the first one highlighted.

But what is that "%11" at the end? Remember, these are link-local addresses, and there is no concept of routing to other networks. Your computer may have or think it has more than one link. If you try using a link-local address and get an error, add the "%11" to the address to tell Windows which link to use. This is the Scope ID and tells Windows which link to look on for specified link-local address. The Scope ID is a Windows-specific concept and isn't really part of IPv6 itself, and the Scope ID never enters the packet or the network. In Linux, most commands have a command line option (e.g. '-i eth0', '-I eth0') to specify the interface link when the address is ambiguous (which is always the case when using link-local addressing when there is more than one interface).

When I first started playing with IPv6 I tried pinging and accessing web sites on my local LAN using the link-local addresses, and it wasn't working. (It's working fine now, so I can't demonstrate failure.) I had to add the %n Scope ID, and then it worked for me. Expect to encounter this issue if you are pinging link-local addresses from a multihomed host.

If you have public or even private IPv6 addresses you can just ignore the link-local addresses. They are used by IPv6 extensively for autoconfiguration, multicasting and neighbor discovery, but they aren't meant to be used by applications or users, and they should never have names resolving to them.