I am also very interested in this question.

Hai, First add the iptables rule for trusted ip's like bellow

#  iptables -A INPUT -p tcp -s ipaddress --dport 22 -j ACCEPT

Next add the rule for block other ip's

#  iptables -A INPUT -p tcp --dport 22 -j DROP

and save new iptables rules.

#  iptables -save