Basic IPtables Firewall for Servers

*filter

#  Allow all loopback traffic
-A INPUT -i lo -j ACCEPT
-A INPUT -i lo -d 127.0.0.0/8 -j REJECT

#  Accept all established inbound connections
-A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT  

#  Allow all outbound traffic
-A OUTPUT -j ACCEPT

#  Allow HTTP and HTTPS connections
-A INPUT -p tcp --dport 80 -j ACCEPT
-A INPUT -p tcp --dport 443 -j ACCEPT

#  Allow SSH connections
#
#  The -dport number should be the same port number you set in sshd_config

-A INPUT -p tcp -m conntrack --ctstate NEW --dport 22 -m recent --set --name SSH
-A INPUT -p tcp -m conntrack --ctstate NEW --dport 22 -m recent --update --seconds 60 --hitcount 4 --rttl --name SSH -j DROP
-A INPUT -p tcp -m conntrack --ctstate NEW --dport 22 -j ACCEPT

#  Allow ping
-A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT

# Allow database connections from a specific source IP address
-A INPUT -p tcp --dport 3306 -s 123.456.789.10/24 -j ACCEPT

#  Log iptables denied calls
-A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7

#  Reject all other inbound traffic
-A INPUT -j REJECT
-A FORWARD -j REJECT

COMMIT