linuxrouter.sh

#!/bin/sh
# Enable IPv4 and IPv6 forwarding / disable ICMP redirect
sysctl -w net.ipv4.ip_forward=1
sysctl -w net.ipv6.conf.all.forwarding=1
sysctl -w net.ipv4.conf.all.accept_redirects=0
sysctl -w net.ipv6.conf.all.accept_redirects=0
sed -i "/net.ipv4.ip_forward=1/ s/# *//" /etc/sysctl.conf
sed -i "/net.ipv6.conf.all.forwarding=1/ s/# *//" /etc/sysctl.conf
sed -i "/net.ipv4.conf.all.accept_redirects = 0/ s/# *//" /etc/sysctl.conf
sed -i "/net.ipv6.conf.all.accept_redirects = 0/ s/# *//" /etc/sysctl.conf

echo "Updating repositories"
sudo apt-get update -y --fix-missing
echo "Installing IPTables-Persistent"
echo iptables-persistent iptables-persistent/autosave_v4 boolean false | sudo debconf-set-selections
echo iptables-persistent iptables-persistent/autosave_v6 boolean false | sudo debconf-set-selections
sudo apt-get -y install iptables-persistent

# Enable NAT to Internet
iptables -t nat -A POSTROUTING -d 10.0.0.0/8 -j ACCEPT
iptables -t nat -A POSTROUTING -d 172.16.0.0/12 -j ACCEPT
iptables -t nat -A POSTROUTING -d 192.168.0.0/16 -j ACCEPT
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

# Save to IPTables file for persistence on reboot
iptables-save > /etc/iptables/rules.v4