If you are using an IPv6 transition technology on a Windows Server 2008 R2 Server Core installation you may experience one or more of the following symptoms:
IPv6 transition technologies such as ISATAP, 6to4 and Teredo do not work correctly when the computer is a member of a network.
You cannot see tunnel adapters for ISATAP, 6to4, or Teredo when you run the ipconfig /all command.
The CPU usage of the Svchost.exe process that hosts the IP Helper service (iphlpsvc) is abnormally high.
You cannot find the Tunnel.sys file on the computer, which should be under %windir%\system32\drivers.
If so, there is a fix available, see article 978309 (http://support.microsoft.com/kb/978309) for more details and the fix.