FAQ

There is a Perl prototype which implements the proof of concept of port knocking. The bulk of this code is detailed in the June 2003 SysAdmin article. Both a client (knockclient) and a server (knockdaemon) are implemented. The prototype is not designed to be used in a production environment. The server implementation monitors the firewall log file for connection attempts. Flexible log format files are supported by defining regular expressions which extract fields of interest. Using a configuration file, which governs what actions are taken when a knock is detected, the server can be programmed to react in an arbitrary way.

In addition to the prototype, there are many other implementations.

All code is licensed under GPL. The conceptual method is not under any license. A number of individuals have implemented home-grown security systems very similar to port knocking (see above).