iptables block everything except ssh code example
Example: iptables block all ssh except 1 ip
iptables -A INPUT -p tcp --dport 22 -s YourIP -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j DROP
iptables -A INPUT -p tcp --dport 22 -s YourIP -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j DROP