basic nat setup with iptables with default OpenVPN network

nat.sh

#!/bin/bash
iptables -F
iptables -t nat -F

iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD DROP

export LAN=ens160 #change to your nic
export WAN=ens192 #change to your nic

echo 1 > /proc/sys/net/ipv4/ip_forward
for f in /proc/sys/net/ipv4/conf/*/rp_filter ; do echo 1 > $f ; done

iptables -I FORWARD -j ACCEPT
iptables -t nat -A POSTROUTING -o ${LAN} -j MASQUERADE
iptables -t nat -A POSTROUTING -o ${WAN} -j MASQUERADE
iptables -t nat -I POSTROUTING -s 10.8.0.0/24 -o ${LAN} -j MASQUERADE
iptables -A FORWARD -i ${LAN} -o ${WAN} -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i ${WAN} -o ${LAN} -j ACCEPT