iptables_openvpn

#!/bin/bash

# REMEMBER: Run this as a single bash script or you'll lock yourself out of your machine.

# Flushing all rules
iptables -F FORWARD
iptables -F INPUT
iptables -F OUTPUT
iptables -X
# Setting default filter policy
iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP
# Allow unlimited traffic on loopback
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
# Accept outbound on the primary interface
iptables -I OUTPUT -o eth0 -d 0.0.0.0/0 -j ACCEPT
# Accept inbound TCP packets
iptables -I INPUT -i eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT
# Allow incoming SSH
iptables -A INPUT -p tcp --dport 22 -m state --state NEW -s 0.0.0.0/0 -j ACCEPT
# Allow incoming OpenVPN
iptables -A INPUT -p udp --dport 1194 -m state --state NEW -s 0.0.0.0/0 -j ACCEPT
# Enable NAT for the VPN
iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE
# Allow TUN interface connections to OpenVPN server
iptables -A INPUT -i tun0 -j ACCEPT
# Allow TUN interface connections to be forwarded through other interfaces
iptables -A FORWARD -i tun0 -j ACCEPT
iptables -A OUTPUT -o tun0 -j ACCEPT
iptables -A FORWARD -i tun0 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i eth0 -o tun+ -m state --state RELATED,ESTABLISHED -j ACCEPT
# Allow outbound access to all networks on the Internet from the VPN
iptables -A FORWARD -i tun0 -s 10.8.0.0/24 -d 0.0.0.0/0 -j ACCEPT
# Block client-to-client routing on the VPN
iptables -A FORWARD -i tun0 -s 10.8.0.0/24 -d 10.8.0.0/24 -j DROP