I have to do with linux firewall iptables quite rarely, that's why I never remember commands I need. I'm going to list them here as they will come on my way.
List rules with line numbers:
iptables -L --line-numbers
Deny all acces from IP, in case of DDOS or Auth-attack:
iptables -A INPUT -s 188.8.131.52 -j DROP
Remove rule by line number: