TCP Wrappers
Most Unix systems use a daemon called inetd (or on Solaris, in.inetd) to respond to the incoming TCP/IP connections. The inetd daemon lies dormant until a request comes in. After a connection is established, the daemon starts the appropriate service and lies dormant again until the next request comes in. However, the standard inetd daemon does not provide access control.
You can use TCP wrappers to solve the restrictions of the inetd daemon. TCP wrappers are intermediate entities that lie between the client and the server. TCP wrappers act as servers until the client sending the request is authenticatedFor example, consider the following example where a client attempts to FTP a server.
Client---->FTP client---->inetd daemon---->FTP---->transfer ...
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