Hello,
If not only one router has Public IP set up PPTP server on it if both have it then it does not matter which one you will use.
In WebUI go to Services > VPN > PPTP choose Role - Server add a name for it and click Add New
New instance will appear in Tunnel name list click on Edit button
In Instance settings window:
1. Enable instance [v].
2. Set local Server IP
3. Set remote devices' IP range.
4. Set User name.
5. Set Password.
6. Set PPTP Clien't IP (I would recommend leaving it empty and client will get first IP from previously set range in this example 192.168.0.21)
7. Press Save
For Client side in same place in WebUI create Client instance and again click Edit on it in the list then:
1. Enable instance [v].
2. Enable "Use as default gateway" if you want to direct yours internet traffic through PPTP server
3. Enable "Client to client" if you wantyour client devices to be able to reach each other (if you will add more client devices)
4. Enter Servers Public IP.
5. Enter User name, that You previously created in Server side.
6. Enter Password that you previously created in Server Side.
7. Press Save
That's it. soon yours PPTP tunnel should be up and you should be able to ping one router from another using their tunnel IP addresses (in this example Server - 192.168.0.1, and Client -192.168.0.21)
Regards,
VidasKac.