ISA Server supports three types of clients:
- Firewall clients are client computers that have Firewall Client installed and enabled.
- Secure network address translation (SecureNAT) clients are client computers that do not have Firewall Client installed and enabled and whose default gateway is set to a directly or indirectly (through a router or chain of routers) reachable IP address of an ISA Server computer.
- Web proxy clients are client applications or computers that send requests to port 80 on an ISA Server computer or to the port on which ISA Server listens for outgoing Web requests from the network in which the client computer resides. Web Proxy clients are typically CERN-compliant applications (Web browser applications) that are configured to send Web requests to an ISA Server computer.
The following table compares the ISA Server clients.
| Feature | SecureNAT client | Firewall client | Web proxy client |
| Installation required | Some network configuration changes are required | Yes | No, but requires configuration of the Web browser |
| Operating system support | Any operating system that supports Transmission Control Protocol/Internet Protocol (TCP/IP) | Only Windows platforms | All platforms, but by way of the Web application |
| Protocol support | Requires application filters for multiple-connection protocols | All Winsock applications | Hypertext Transfer Protocol (HTTP), Secure HTTP (HTTPS), and File Transfer Protocol (FTP) (download requests) |
| User-level authentication | Only the IP address of the user is sent to the ISA Server computer. | The Firewall Client software sends the user's credentials to the ISA Server computer with each request. | User credenticals can be supplied in response to requests from ISA Server. |
| Server applications | No configuration or installation required | Requires configuration file | N/A |
Web proxy clients can run on Firewall client computers and on SecureNAT client computers. If the Web application on the computer is configured explicitly to use an ISA Server computer, then all Web requests (HTTP, HTTPS, and FTP) are sent to the ISA Server Web proxy.
This section contains the following topics: