We had an issue on a customer recently on a Windows 2012 R2 Direct Access server, where no DA clients could connect over Teredo and in the Remote Access monitoring page, Teredo was being marked as failed.
If we ran “netsh int teredo show state” we could see the following error:
Error: Unable to open primary socket
After much troubleshooting the issue turned out to be McAfee, we tried disabling the MacAfee services on the DA server, however the issue persisted.
But as soon as we uninstalled McAfee completely everything kicked into life and all the Teredo issues disappeared J