Shell script to set up an ssh vpn tunnel and set default routes.

nat.bash

#!/bin/bash

if [[ $# < 2 ]]
then
        INTERNAL=tun0
        EXTERNAL=eth0
else
        INTERNAL=$1
        EXTERNAL=$2
fi

echo 1 > /proc/sys/net/ipv4/ip_forward

iptables -t nat -A POSTROUTING -o $EXTERNAL -j MASQUERADE
iptables -A FORWARD -i $EXTERNAL -o $EXTERNAL -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i $INTERNAL -o $EXTERNAL -j ACCEPT

ssh_vpn.sh

#!/bin/bash

sudo ssh -w0:0 $@ true &
#tmux new-session -d "sudo ssh -w0:0 $@ true"
sleep 3
sudo ssh "$@" "ifconfig tun0 192.168.42.1 netmask 255.255.255.0"
sudo ifconfig tun0 192.168.42.2 netmask 255.255.255.0
ping -c 1 192.168.42.1 2> /dev/null > /dev/null
ret=$?
if [[ "$ret" -ne "0" ]]
then
	echo "Tunnel setup failed."
	exit 1
fi

gateway=$(route -n | grep 0.0.0.0 | head -n 1 | awk '{print $2}')
host=$(echo "$@" | awk '{ print $NF }')
sudo route add -net $host netmask 255.255.255.255 gw $gateway
sudo route del default
sudo route add default gw 192.168.42.1