It is not all that uncommon to find people using built-in cellular modems, EVDO cards or tethering of mobile phones to connect their laptop to the Internet. When the laptop is enabled for DirectAccess the user is able to function as normal (they can reach into the corpnet) but the IT staff may discover that they are unable to establish a connection to the DirectAccess computer (manage-out fails). As
Daniele Francioni pointed out on UAG Team blog, the problem often boils down to the fact that Dial-up connections, by default, do not register their hostname with DNS!
If you knew the IPv6 address of the DirectAccess client then you could use that to connect to it, but that's not very helpful. To fix it so you can connect by name, simply check the box to Register DNS on the properties of the adapter being used to connect the client to the Internet. Here's an example on a Sierra Wireless card used to connect to a 3G network like Sprint, Verizon or AT&T.
- From the Network Connections control panel, Right click the adapter and select Properties
- Select the Networking tab, highlight TCP/IPv4 and click the Properties button
- From the General tab click the Advanced button
- On the DNS tab check "Register this connection's IP address in DNS"
Once you have that checked and re-establish a connection you should find the DA client's IPv6 address in DNS and you can manage it using Remote Desktop or any other IPv6 aware software you wish.