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Is it possible to implement a simple code lock triggered by connecting ports with iptables? So for example a visitor need to connect ports 1001,1009,1008,1004 in this order to get access to port 80. Any other port hit out of order in the range 1000-1009 would reset the lock.

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up vote 6 down vote accepted

This strategy is known as "port-knocking" and there are numerous implementations.

See this link for a large list, pretty linux-centric: http://portknocking.org/view/implementations

And the Wikipedia entry: https://en.wikipedia.org/wiki/Port_knocking

Here's an iptables-only version (which I personally find revolting): http://www.debian-administration.org/articles/268

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ok, as it seems iptables alone can not provide this. If this holds, I will accept this answer. –  dronus Feb 20 at 3:37
    
Edited to include iptables-only example. –  quadruplebucky Feb 20 at 3:58
    
Fantastic! Will check this out. –  dronus Feb 20 at 10:55

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