sudo vim /etc/init.d/firewall
### BEGIN INIT INFO
# Provides: firewall rules
# Required-Start: $remote_fs $syslog
# Required-Stop: $remote_fs $syslog
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: Start daemon at boot time
# Description: Enable service provided by daemon.
### END INIT INFO
#!/bin/sh
# Vider les tables actuelles
iptables -t filter -F
# Vider les règles personnelles
iptables -t filter -X
# Interdire toute connexion entrante et sortante
iptables -t filter -P INPUT DROP
iptables -t filter -P FORWARD DROP
iptables -t filter -P OUTPUT DROP
# Ne pas casser les connexions etablies
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
# Autoriser le loopback
iptables -t filter -A INPUT -i lo -j ACCEPT
iptables -t filter -A OUTPUT -o lo -j ACCEPT
# ICMP (ping)
iptables -t filter -A INPUT -p icmp -j ACCEPT
iptables -t filter -A OUTPUT -p icmp -j ACCEPT
# FTP (BACKUP)
iptables -t filter -A INPUT -p tcp --dport 21 -j ACCEPT
iptables -t filter -A OUTPUT -p tcp --dport 21 -j ACCEPT
# SSH
iptables -t filter -A INPUT -p tcp --dport 22 -j ACCEPT
iptables -t filter -A OUTPUT -p tcp --dport 22 -j ACCEPT
# DNS (bind)
iptables -t filter -A OUTPUT -p tcp --dport 53 -j ACCEPT
iptables -t filter -A OUTPUT -p udp --dport 53 -j ACCEPT
iptables -t filter -A INPUT -p tcp --dport 53 -j ACCEPT
iptables -t filter -A INPUT -p udp --dport 53 -j ACCEPT
# APACHE : HTTP + HTTPS
iptables -t filter -A OUTPUT -p tcp --dport 80 -j ACCEPT
iptables -t filter -A OUTPUT -p tcp --dport 443 -j ACCEPT
iptables -t filter -A INPUT -p tcp --dport 80 -j ACCEPT
iptables -t filter -A INPUT -p tcp --dport 443 -j ACCEPT
# Mail SMTP:25
iptables -t filter -A INPUT -p tcp --dport 25 -j ACCEPT
iptables -t filter -A OUTPUT -p tcp --dport 25 -j ACCEPT
# Mail POP3:110
iptables -t filter -A INPUT -p tcp --dport 110 -j ACCEPT
iptables -t filter -A OUTPUT -p tcp --dport 110 -j ACCEPT
# Mail IMAP:143
iptables -t filter -A INPUT -p tcp --dport 143 -j ACCEPT
iptables -t filter -A OUTPUT -p tcp --dport 143 -j ACCEPT
# Mail POP3S:995
iptables -t filter -A INPUT -p tcp --dport 995 -j ACCEPT
iptables -t filter -A OUTPUT -p tcp --dport 995 -j ACCEPT
# WEBMIN
iptables -t filter -A INPUT -p tcp --dport 10000 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -t filter -A OUTPUT -p tcp --dport 10000 -m state --state ESTABLISHED -j ACCEPT
sudo chmod +x /etc/init.d/firewall
sudo sh /etc/init.d/firewall
sudo update-rc.d firewall defaults
Source : https://www.skyminds.net/serveur-dedie-securisation-des-services-avec-iptables-et-fail2ban