Installing and Using ISA Server as a Firewall

Microsoft Internet Security and Acceleration (ISA) Server 2000 is an enterprise firewall and Web cache. You can install ISA Server in three modes: Cache, Firewall, or Integrated (which provides both cache and firewall capabilities). Because you're using ISA Server as a firewall, you should select either Firewall or Integrated mode. With ISA Server, you can control every aspect of how clients on the internal network can access resources on the Internet.

To implement a demilitarized zone (DMZ), you need to configure your computers on the internal network to access ISA Server as SecureNAT clients, not as ISA Server firewall clients or Web proxy clients. SecureNAT means that you configure the internal network with a private IP subnet and let ISA Server use Network Address Translation (NAT) to service Internet requests from internal clients. Using SecureNAT simply requires you to configure computers on your internal network to use the ISA Server as the default gateway. You don't need to load any ISA Server­related software on those computers. When using SecureNAT, you need to make sure that all computers requiring access to the Internet are configured with the IP address of your ISP's DNS server on the Internet or that your internal DNS server forwards unresolved queries to your ISP's DNS server or another Internet-accessible DNS server. . . .