There is in fact. Port knocking to open a port (and a service behind it) which is presumably closed at start. oversimplification: CLIENT> POKE POKE SERVER> TC

There is in fact. Port knocking to open a port (and a service behind it) which is presumably closed at start. oversimplification: CLIENT> POKE POKE SERVER> TCP RST, nothing to SEE HERE CLIENT> POKE POKE POKE <SPACE> POKE POKE POKE (i insist in proper way) SERVER> TCP ACK (I oblige) More: https://www.digitalocean.com/community/tutorials/how-to-configure-port-knocking-using-only-iptables-on-an-ubuntu-vps https://www.digitalocean.com/community/tutorials/how-to-conf...