ISATAP is the Intra-site Automatic Tunnel Addressing Protocol. ISATAP is an IPv6 transition technology that allows you to use IPv6 applications on a IPv4 network. For example, support you have a new application called AppA. This application is designed to take advantage of the IPv6 networking protocol, but your network isn't designed to support IPv6. Your routers only work with IPv4, your DNS infrastructure is based on IPv4, your DHCP servers are designed to work only with IPv4, and you just don't want to deal with IPv6. However, you are interested in AppA - so you want to get this IPv6 application working on your IPv4 network.
ISATAP can help you get AppA to work. ISATAP will encapsulate the IPv6 packets with an IPv4 header before sending them out to the network. While on the network, the IPv6 packets travel inside the IPv4 header, so that they can be routed throughout your IPv4 network using your IPv4 routing infrastructure. Once the packet reaches the destination, the IPv4 header is removed from the packet, and the IPv6 packet is revealed to AppA.
This allows you to use your IPv4 instructure and use AppA, which is designed for IPv6. This is how DirectAccess takes advantage of ISATAP. The DirectAccess client always speaks IPv6, and so when it connects to resources on the corpnet, it will use the IPv6 address of the server on your network, which is the ISATAP address of the server on your network.
< Message edited by tshinder -- 5.Apr.2010 8:18:03 AM >