While many firms are moving toward an IPv6 capable or aware network, many more networks are not IPv6 capable.
What do I mean by IPv6 capable? Essentially, its a network that can use IPv6 addresses. These can be native IPv6 addresses, where you assign IPv6 addresses manually of over DHCP or via autoconfiguration, or when you have client systems that can use ISATAP to tunnel IPv6 messsages over an IPv4 network. Windows Vista and above and Windows Server 2008 and above support ISATAP, making these operating systems IPv6 capable.
But what if you don't have IPv6 capable servers? Or maybe you have a couple IPv6 capable servers, but most of your important assets are on Windows 2003 or even Windows 2000, or non-Windows operating systems that don't support ISATAP or native IPv6?
If you're using the Windows only DirectAccess server, then you're out of luck. Windows Server DirectAccess servers require that you have an IPv6 infrastructure behind the DA server.
However, if you are using UAG, then you're in good shape. Why? Because UAG includes NAT64/DNS64, which allows you to have an IPv4 only network behind the UAG DA server. So your file servers, mail servers, domain controllers, and any other server behind the UAG DA server is accessible from the DA client.
So, if you're IPv4 only - no worries. Just use UAG for your DirectAccess server and you'll be able to get most of the benefits you get from DirectAccess. There are a couple of limitations, but we'll cover those in another forum post.