Index of /ports_security/knock

 Name                    Last modified      Size  
 Parent Directory                             -   
 Makefile                28-May-2011 14:11  1.8K  
 distinfo                12-Jul-2006 22:03  210   
 files/                  07-Jun-2010 13:13    -   
 pkg-descr               31-Aug-2009 12:31  604   

knockd is a port-knock server. It listens to all traffic on an ethernet
(or PPP) interface, looking for special "knock" sequences of port-hits.

A client makes these port-hits by sending a TCP (or UDP) packet to a
port on the server. This port need not be open -- since knockd listens
at the link-layer level, it sees all traffic even if it's destined for
a closed port. When the server detects a specific sequence of port-hits
port-hits, it runs a command defined in its configuration file. This
can be used to open up holes in a firewall for quick access. 

WWW: http://www.zeroflux.org/projects/knock