IPv6 Connectivity and Teredo
Most networks are IPv4-only and end-to-end IPv6 connectivity is not easily obtainable. Additionally, most NAT devices even limit end-to-end IPv4 connectivity. With Windows Vista, IPv6 end-to-end connectivity between any two hosts is possible. Developers no longer have to worry about end-to-end connectivity, but rather create new application scenarios that enable them to take advantage of this connectivity.
The goal of Teredo, as an IPv6 transition technology, is to make end-to-end IPv6 connectivity simple and automatic. In many cases, developers may not even need to know that transition technologies like Teredo exist in Windows Vista. Windows Vista has the capability to use Teredo in the background as a seamless method of IPv6 connectivity.