6to4 is used only when your DirectAccess client computer is assigned a public IP address. IP-HTTPS is a low performance, high overhead solution, and therefore you’d want to avoid that. The majority of your connections will be Teredo connections.
The DirectAccess client will use Teredo to connect to the UAG DirectAccess server when the client is located behind a NAT device.
But the story is a little more involved than that. In his article DirectAccess and Teredo Adapter Behavior, the Edge Man, Tom Shinder, goes into the technical details of the Teredo adapter and how it’s controlled for the DirectAccess client.
Check out Tom’s article over at:
DEBRA LITTLEJOHN SHINDER
MVP (Enterprise Security)