Winsock Proxy service is the only service offered that supports IPX/SPX as well as TCP/IP as a protocol of choice. When IPX is used, conversion of IPX to IP is done twice, once when the information leaves the network for the Internet, and once on its return. This is necessary since the Internet is solely a TCP/IP-based network. Winsock Proxy is compatible with Windows Sockets applications and operates with them as if they had a straight connection to the Internet. Winsock Proxy service does not cache Internet addresses or support routing like the Web Proxy service does, but it does offer the ability to add protocols other than FTP, Gopher, Secure, and WWW. With Winsock Proxy service, protocols such as Post Office Protocol 3 (POP3), Hypertext Transfer Protocol (HTTP), and Real Audio can be added simply by configuring them through the Internet Service Manager. With Winsock Proxy service, both inbound and outbound access can be secured by placing permissions on protocols, port numbers, users, or groups. IP addresses, domain names, and IP address ranges can also be used to restrict users’ access to the Internet. External users can be blocked from accessing the internal network using this service. Clients that use the Winsock Proxy service must be using a Windows operating system. This rules out this service for many networks since there are usually other clients like Novell or UNIX. As with the other services, logging is enabled and can be used to track client usage.