IPTABLES
iptables -F

//1.
iptables -A input -p tcp - -dport 22 -m limit - -limit 1/m - -limit -burst 3 -j ACCEPT
//2
iptables -A input -i eth1 -p tcp - -dport21 -j ACCEPT
iptables -A output -i eth1 -p tcp - -dport21 -j ACCEPT
//3
iptables -A input -s 182.168.123.31 -j DROP
iptables -A output -d 182.168.123.31 -j DROP