iptables use linux as windows gateway and forward target connect to linux local port

created: 20240425 updated: 20240425 authors: alick97

background

• use linux as gateway
• window10 pc config gateway to linux
• window10 connect to public ip port 112.60.14.252:6666, linux not send this connect, redirect it to local
• router ip 192.168.31.1
• linux ip 192.168.31.158
• window10 ip 192.168.31.172
• window10 and linux connect to router

in win, config window10 gateway

• control panel -> internat -> connect -> property -> TCP/IPv4 -> property

  ip 192.168.31.172
  netmask 255.255.255.0
  gateway 192.168.31.158   (linux pc ip)
  

• dns server

  114.114.114.114
  8.8.8.8
  

  in linux config forward and start http server

• config ip forward

  sysctl -w net.ipv4.ip_forward=1
  

• config gateway rule by iptables, wlo1 is net out interface

  sudo iptables -t nat -A POSTROUTING -s 192.168.31.172 -o wlo1  -j MASQUERADE
  

• config redirect rule by iptables for special windows10 connect

  sudo iptables -t nat -A PREROUTING -p tcp -d 112.60.14.252 --dport 6666 -j DNAT --to 192.168.31.158:7777
  sudo service iptables restart
  

• start demo server in linux

  python3 -m http.server  7777
  

in win, access target url

• in browser access http://112.60.14.252:6666/
• all will be sended to linux 7777 port
• in wireshark see ip.addr == 112.60.14.252

more iptables

http://cn.linux.vbird.org/linux_server/0250simple_firewall.php#nat_what

https://www.karlrupp.net/en/computer/nat_tutorial