Systems and methods for controlling the number of clients that can access a server in a server-client network are described. A communications filter driver resides on the server and monitors network communications to determine a unique network address of each client that attempts to access the server. When a client attempts to access the server, the server allows the client to access the server if the network address of the client is listed in a table. If the network address of the client is not listed in the table, the server determines if a client limit has been met or exceeded. If the limit has been reached, the server determines if the client is a client that has previously accessed the server under a different network address. This is accomplished by sending a signal to each network address listed in the table and requesting a response.