ISA Server 2000 provides firewall functionality by monitoring all incoming and outgoing Internet network traffic. A firewall protects your local network from unauthorised Internet access by permitting only packets that meet predefined criteria to reach the local network.
To configure the criteria for which packets are permitted to access the Small Business Server computer, run the Small Business Server Internet Connection Wizard.

When you run the wizard, you can define the types of network traffic you want to allow access to and from your local network. For example, you can permit e-mail traffic to and from the Internet.
By running the Small Business Server Internet Connection Wizard, you can configure ISA Server to securely open communications that are necessary for your Small Business Server computer and client computers to connect to the Internet. When you run the wizard, the following firewall configurations are made:

• Internet requests made by members of the Small Business Internet Users group will be forwarded based on the BackOffice Internet Access Protocol Rule and BackOffice Internet Access Site and Content Rule.
• A standard set of filters necessary to ensure your Internet connectivity will be created. After installation, ISA Server effectively blocks all communication between your local network and the Internet. These standard filters are necessary for client computers and the Small Business Server computer to access the Internet.
• By enabling ISA Server packet filtering, additional services are permitted to access your network, such as e-mail and virtual private networking.
• To prevent unnecessary connections to the Internet, active caching is disabled.