How to SECURE SSH - Port Knocking on Ubuntu |Knock-Knock | Linux Containers

Port knocking ???

•   Simple method to grant remote access without leaving a port constantly   open.
• preserves our server from port scanning and script kiddie attack

Implementation: 

• implemented by generating a connection attempt on a prespecified closed ports 
• once a correct sequence of connection attempt is met firewall rules are dynamically manipulated

  
 Much of a theory!! lets just try and see....

References:
  https://help.ubuntu.com/community/PortKnocking

Note:
  Simple portknocking daemons (such as knockd) are vulnerable because a sniffer may recover the port sequence that was used. A better solution is Cryptknock (http://cryptknock.sourceforge.net/)