Force Traffic Through a VPN via UFW (uncomplicated firewall)

vpnonly.sh

#!/bin/bash
# Check root. So we don't need it everytime.
if [[ $EUID -ne 0 ]]; then
   echo "Got root?"
   exit 1
fi

# VPN's listening port:
vpnPORT=1194
# Interface (usually tun0 or tap0)
vpnITF=tun0

# Flush our current chains:
# iptables -F
# iptables -t nat -F
# iptables -t mangle -F
# iptables -X

# Make sure UFW doesn't break anything
ufw reset

# UFW defaults:
ufw default deny incoming
ufw default deny outgoing
ufw default deny forward

# DNS Queries should pass to initiate the connection
ufw allow out 53
ufw allow out $vpnPORT

# Allow out on virtual NIC
ufw allow out on $vpnITF 

#Note: If there are any private subnets you need to 
# reach while you are connected to the VPN, add them here:
#ufw allow out on eth0 to 192.168.1.0/24 

# Ensure access to all private networks.
# You may want to restrict these to certain subnets, up to you.
ufw allow out to 192.168.0.0/16
ufw allow out to 172.16.0.0/12
ufw allow out to 10.0.0.0/8

# Allow ipv4 muticast
ufw allow out to 224.0.0.0/24
ufw allow out to 239.0.0.0/8

# Allow local ipv6
ufw allow out to ff01::/16

# Turn all rules on
ufw enable