Windows Tip: Know your IPv6 address types

July 21, 2006 —

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Is your enterprise planning or in the process of migrating your IPv4 network to IPv6? Did you know Windows Vista comes with IPv6 enabled out-of-the-box? And were you aware that some Vista applications like Windows Meeting Space use only IPv6 and not IPv4?

If you're not familiar with IPv6 yet, it's time you should be. One place to start is to get to know how to recognize the various types of v6 addresses. Every administrator already knows these common v4 addresses: 127.0.0.1 (loopback), 10.0.0.0 to 10.255.255.255 (class A private network), 172.16.0.0 to 172.16.31.255 (class B private networks), 192.168.0.0 to 192.168.255.255 (class C private networks), and so on. Most of us also know that 169.254.0.0 to 169.254.255.255 are used by APIPA (Automatic IP Addressing), a feature that Windows machines use to self-assign an address when they can't find a DHCP server. And some of us may even know that 224.53.2.45 is an example of a multicast address.

What are the special addresses we need to know for IPv6? Here's a quick guide to interpreting commonly used v6 addresses:

> The loopback address is now ::1

> Link-local addresses (self-assigned v6 addresses) always start with fe80::

> Site-local addresses start with fec0::

> Multicast addresses begin with ff

> ISATAP addresses end with 0:5efe:w.x.y.z where w.x.y.z is an IPv4 address

> Finally, if you see nothing but :: then your interface doesn't have a v6 address

Memorizing this list can be useful. For example, if you type ipconfig /all on a Windows Vista machine, you'll see a list of interfaces that should include several v6 addresses. Try it sometime and start learning to recognize the different types of IPv6 addreses. You'll probably need this knowledge once you have Vista running on your desktops, especially if you want to troubleshoot an application like Meeting Space.

ITworld.com