The main goals of ISA Server are to insulate the network from hackers, improve Internet performance for clients on the network, and control client access to the Internet.
ISA Server maintains control of connectivity and isolates the internal network by having two (or more) completely separate physical connections—one to the Internet and one to the internal network. Each network is connected to a different network card, and all packets must pass through the ISA Server software to get from one connection to the other.
The mechanisms that ISA Server uses to achieve these aims are fairly straightforward. The following three basic techniques are used:
Network address translation
The following sections discuss each ...