#!/bin/bash
# This script is written to make your Linux machine Router
# With this you can setup your linux machine as gateway.
# Author @ Mansur Ul Hasan
# Email  @ mansurali901@gmail.com

# Defining interfaces for gateway.
INTERNET=wlp1s0
LOCAL=enp2s0.1

# IMPORTANT: Activate IP-forwarding in the kernel!

# Disabled by default!
echo "1" > /proc/sys/net/ipv4/ip_forward

# Load various modules. Usually they are already loaded 

# Load iptables module:
modprobe ip_tables
# activate connection tracking
# (connection's status are taken into account)
modprobe ip_conntrack
# Special features for IRC:
modprobe ip_conntrack_irc
# Special features for FTP:
modprobe ip_conntrack_ftp
# Deleting all the rules in INPUT, OUTPUT and FILTER   
iptables --flush
# Flush all the rules in nat table 
iptables --table nat --flush
# Delete all existing chains
iptables --delete-chain
# Delete all chains that are not in default filter and nat table
iptables --table nat --delete-chain
# Allow established connections from the public interface.
iptables -A INPUT -i $INTERNET -m state --state ESTABLISHED,RELATED -j ACCEPT
# Set up IP FORWARDing and Masquerading
iptables --table nat --append POSTROUTING --out-interface $INTERNET -j MASQUERADE
iptables --append FORWARD --in-interface $LOCAL -j ACCEPT
# Allow outgoing connections
iptables -A OUTPUT -j ACCEPT