Linux.PortKnocking

Brief description from www.portknocking.org: Port knocking is a method of establishing a connection to a networked computer that has no open ports look up ports on webopedia.com look up ports on FOLDOC . Before a connection is established, ports are opened using a port knock sequence, which is a series of connection attempts to closed ports. A remote host generates and sends an authentic knock sequence in order to manipulate the server's firewall look up firewall on webopedia.com look up firewall on FOLDOC rules to open one or more specific ports. These manipulations are mediated by a port knock daemon, running on the server, which monitors the firewall log file for connection attempts which can be translated into authentic knock sequences. Once the desired ports are opened, the remote host can establish a connection and begin a session. Another knock sequence may be used to trigger the closing of the port.

• Portknocking.org - links links to resources and a prototype application
• Linux Security article about PortKnocking
• SAdoor - a client/daemon implementation of portknocking
• A Linuxsecurity article about setting up/using SAdoor
• Doorman - another client/daemon implementation of portknocking

Instructions for applying this to your Linux/Debian system: To be continued…