You all know these old gangster films where a guy uses a knock sequence on a door to get in? Port Knocking is exactly that, just for your server. Installing port knocking on Ubuntu is easy. I will show you in this article how to install and set up port knocking. The steps from this tutorials should work for Debian 8 as well.
March 15, 2016
How to use Port Knocking on Ubuntu to hide the SSH port
Read more at HowtoForge