Very basic IPTables reference
How to block an IP address in Linux from ssh:
DROP anything coming from the IP address 1.2.3.4:
append will put this new rule at the end of your ruleset:
iptables -A INPUT -s 1.2.3.4 -j DROP
with insert you can tell which position you want your rule to be:
iptables -I INPUT 3 -s 1.2.3.4 -j DROP
When you insert the rule will not replace the existing one.
list rules:
iptables -L
list specific INPUT rules:
iptables -L INPUT
find where the rule is in the list, #1 at the top, and delete it:
iptables -D INPUT 3
(removes rule #3 from “INPUT”)