I recently found a very useful command in Linux named ‘tcpkill’. Actually, the other day I was trying to find a way to kill a tcp connection between my server and a client. Not that it was an attack or needed firewall rule, but simply I wanted it to be killed in order to let the upper layer application to re-establish connection. There was no utility in the upper layer application to do this and it handed TCP connection management over to OS (TCP KEEPALIVE in linux kernel). So, I started looking for the solution to kill the connection.
So, the solution was easy, just issue ‘tcpkill’ command with appropriate parameters. Parameters are compliant with ‘tcpdump’ filter formats. So, if you are familiar with ‘tcpdump’ you will find it easy. For more explanation, examples see the amazing cyberciti website.