If you are using iptables for your machine Firewall.
Below script might help to lock down SSH access which only allow specific IP to connect via SSH.
##########################
# LOCK DOWN
##########################
for IP in 111.111.111.111 222.222.222.222 333.333.333.333 444.444.444.444/27 ; do
/sbin/iptables -A INPUT -p tcp -s $IP –dport (SSH PORT)-j ACCEPT
/sbin/iptables -A OUTPUT -p tcp -d $IP –sport (SSH PORT)-j ACCEPT
done
iptables -A INPUT -p tcp –dport (SSH PORT) -j DROP
iptables -A OUTPUT -p tcp –sport (SSH PORT)-j DROP
#####################
Make sure to change (SSH PORT) to your SSH Port.
Hope this would be useful.
