DirectAccess requires two public IP-addresses on the external network interface (NIC). This is clearly documented in the DirectAccess deployment guide on TechNet. Unfortunately, the UAG user interface does not validate for public IP-addresses on the external NIC. If private IP-addresses were configured on the external NIC, it can be assigned in the UAG DirectAccess Server Configuration. A future version of UAG should check the Internet-facing IP-addresses for validity.
If private IP-addresses are used on the Internet-facing NIC, the following error occurs when activating the configuration.
To solve the problem, you must change the Internet-facing IP-addresses to public addresses in the NIC configuration. Assign the Internet-facing address in the UAG DirectAccess Server Configuration to a public address and activate the UAG configuration.