How to access a 4G modem on a local router through a remote server using 3proxy and PPTP VPN?

Question

VPN

Hello.
I’ll make a reservation right away that I’m weak in networks, so the help of specialists is required.
Since the mobile operator provides a gray IP, you can’t get direct access to the router from the outside, so I decided to try to organize a VPN channel with a remote server and access the router through this channel.
Available.

• Remote VPS server on Ubuntu 16.04 with external IP 200.2.2.2, on which 3proxy and PPTP VPN server are up.
  
• A local Keenetic 4G III router that receives the Internet via a 4G modem connected to the USB port with HiLink firmware and a built-in PPTP client
  

What is done.

• A PPTP channel is configured between the server and the router. The router is assigned IP 10.0.0.100
  
• 3proxy is configured on the server so that all requests on port 3002 are directed to IP 10.0.0.100
  socks -n -p3002 -e10.0.0.100
  
• According to the manual found on the Internet for setting up a PPTP server, IP forwarding is enabled (net.ipv4.ip_forward = 1) and a rule for iptables is added:
  

  sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

  
  
• The router is configured to forward all ports from the PPTP0 interface to the 4G modem IP 192.168.8.100
  
  

Result.
3proxy logs when requesting ya.ru:

1541685862.458 SOCK5.3002 00012 userlogin 200.2.2.2:51288 87.250.250.242:443 0 0 0 CONNECT_ya.ru:443

It follows from the logs that 0 bytes received, 0 bytes sent.
Questions.

1. Is it possible in principle to implement this with the current hardware and software?
   
2. If yes, what am I doing wrong?
   

Answer 1

It follows from the logs that not 0 bytes were received, but that you incorrectly specified the external interface in the 3proxy configuration,
https://3proxy.ru/howtor.asp#ERRORS
https://3proxy.ru/faqr.asp#INTEXT