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PPTP-HOWTO.md

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As well as allowing DOSbox connections, ipxbox also allows connections using the PPTP protocol. This is a VPN protocol that is supported natively by Windows 95, 98 and Me. If you have a retro computer running one of these operating systems, you can therefore use this feature to connect to a server and play with DOSbox clients (or others using PPTP as well).

Client setup

First check that the ipxbox server you're connecting to has PPTP support enabled - by default it is disabled. If you're running your own server, check the "Server setup" section below.

Windows 98 and Me both shipped with PPTP VPN support, but if you're using Windows 95 you'll need to install the Dial-up Netwokring 1.4 Upgrade. This was distributed for free by Microsoft with the filename MSDUN14.exe.

VPN support is an optional OS component that might not be installed on your system. First check that it is installed by going to Control Panel → Add/Remove Programs → Windows Setup. Open the Communications component and ensure that "Virtual Private Networking" is ticked.

             Add/Remove Programs Dialog

If not installed, Windows will prompt you for the Windows install CD in order to install it. Once installed, open "My Computer" → Dial-up Networking and create a new connection. Select "Microsoft VPN Adapter" as the device, and on the second page, type the host name or IP address of the ipxbox server.

             New Connection Wizard Page 1

             New Connection Wizard Page 2

Now you can try out your new connection. Open it from the "Dial-up Networking" window and you should see a dialog similar to the following:

             DUN "Connect To" dialog

Check again that the VPN server address is correct, then press "Connect". It doesn't matter what you enter in the User name and Password fields - these aren't used. If everything is set up right, it should connect succesfully and you will see the Dial-up Networking window minimize to the systray (you can re-open it to disconnect).

You may see that it starts to connect but you then get disconnected by the server. If this happens, it is possible that you don't have the IPX protocol installed. To check, go to Control Panel → Network, and check the list of network components.

             Network Settings dialog

Check that at least the following are present:

  • IPX/SPX-compatible Protocol -> Dial-Up Adapter #2 (VPN support)
  • IPX/SPX-compatible Protocol -> Microsoft Virtual Private Networking Adapter

If these aren't present, click "Add...". For component type, choose "Protocol" and click "Add...". Then choose "Microsoft" as the manufacturer and select "IPX/SPX-compatible Protocol":

             Add Network Protocol windows

Windows will prompt you for the Windows install CD in order to install the protocol. Once installed, go back and try again to connect to the VPN.

Server setup

First of all, start by following the basic instructions for how to set up an ipxbox server.

By default ipxbox only runs a DOSbox-protocol server, and PPTP is disabled. To enable it, add --enable_pptp to the command line (if running with systemd, make sure to update your configuration file). For example, the command might now look like:

ipxbox --enable_syslog --port=10500 --enable_pptp

The PPTP protocol uses GRE tunneling, and sending/receiving GRE packets requires raw sockets access. Therefore on a Linux system you will want to grant ipxbox the capability it needs:

sudo setcap cap_net_raw,cap_net_admin=eip ./ipxbox

You can test the feature by having someone connect to your server. It is better to get someone outside your network to test it, to make absolutely sure that it is accessible to the world. If they can't connect, the following are some ideas:

  1. If the server is running on a home network, you may need to set up port forwards. The way to do this depends on your Internet router, and instructures vary. You need to forward TCP port 1723, along with all GRE packets (IP protocol 47). Some routers have built-in support for PPTP traversal, so even if there's no way to forward GRE packets, you might find that it works anyway.

  2. Check if a firewall is set up on the server where ipxbox is running. If there is, you may need to add a firewall exception. Linux firewalls use iptables, and the following commands are an example of how to add an exception:

sudo iptables -A INPUT --dport 1723 -p tcp -j ACCEPT
sudo iptables -A INPUT -p gre -j ACCEPT