How to enable a port forwarding script - with iptables

port_forwarding.md

#!/bin/bash

echo 1 > /proc/sys/net/ipv4/ip_forward # must be enabled for the forwarding to work

iptables -F 
iptables -t nat -F  # flush the nat table
iptables -t mangle -F
iptables -X


# Source
# https://serverfault.com/questions/765071/iptables-forward-all-traffic-to-a-specified-port-to-another-device

## TCP

# we want to forward from the linux_machine to the windows_server

windows_server='192.168.128.18'
linux_machine='192.168.128.7'

iptables -t nat -A PREROUTING -p tcp --dport 1237 -j DNAT --to-destination $windows_server:1237
iptables -t nat -A POSTROUTING -p tcp -d $windows_server --dport 1237 -j SNAT --to-source $linux_machine

iptables -t nat -A PREROUTING -p tcp --dport 1238 -j DNAT --to-destination $windows_server:1238
iptables -t nat -A POSTROUTING -p tcp -d $windows_server --dport 1238 -j SNAT --to-source $linux_machine

echo -e $(iptables --table nat --list)

# to run
# sudo ./port_forwarding.sh