pi-zero-forwarding.sh

# First, setup the vpn on your pi-zero. For me, this entails

openfortinet -c vpn

# This will create a ppp0 interface, via which we want to allow tunneling to the whole network.

sysctl -w net.ipv4.ip_forward=1

iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE

iptables -A FORWARD -i wlan0 -o ppp0 -j ACCEPT

iptables -A FORWARD -i ppp0 -o wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT

iptables -A INPUT -i lo -j ACCEPT

iptables -A INPUT -i wlan0 -p icmp -j ACCEPT

iptables -A INPUT -i wlan0 -p tcp --dport 22 -j ACCEPT

iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

iptables -P FORWARD DROP
iptables -P INPUT DROP
iptables -L

# Since we want these commands to persist on reboot

 apt-get install iptables-persistent
 systemctl enable netfilter-persistent
 
 # Afterwards, either set the pi as the default gateway on your network, or add specific routes like this
 
 sudo route add -net 172.16.77.28 -gateway 192.168.0.10