@Aarix 

Hey

Can I ask what device you are using to access the WAN?  You do mention its a MODEM, is this actually a router?

I cant say for certain but the WAN IP you have is 192.168.0.1 which is more common on a Modem/Router than a modem.  On a direct modem connection I would expect to see this as your WAN IP  147.10.11.12  something along those lines.   192.168 indicates a DHCP server, therefore a router.

If that is the case and your WAN modem does have a router functionality you would need to set port forwarding for the VPN ports on the WAN router..   for pptp i think this is 47 and 1723 if memory is correct.    

While there i would also recommend changing the IP Address on the WAN router to a subnet outside your LAN range   192.168.10.x or something similar.   While not required, it would be advised.  

All being setup correct your WAN Router should be addressed as 192.168.10.1     all traffic on 47 and 1723 going to   192.168.10.2 (or whatever address it allocates to your R600 WAN port)  which will then route to   192.168.0.x   and serve your clients..

@Philbert 

Thank you immensely for offering your time to help me.

Yes the modem is a combo. Sorry for not making that clear. Am I wrong in assuming placing the TL-R600VPN in a DMZ nullify the need for port forwarding since the Firewall is not being used?

I'm not too certain how WAN would work in this context on the TL-R600VPN. I didn't ask any questions when it said link was up and was pinging 8.8.8.8. It's set to 192.168.0.30. I didn't have a high desire to subnet (especially since I'm first trying to understand everything without adding that layer to things). I just wanted any device that connects to the TL-R600VPN to be in the same network and I can harden things later when I get a better handle. In theory the device that connects using TL-R600VPN should have a virtual IP of 192.168.0.2XX then. I'll try to connect with those ports open too.

@Aarix 

In this setup a DMZ is really no use, you are going to need to forward the ports through the router, this should be easy enough done.    I would recommend removing it from the DMZ and sticking the firewall back on, its ultimately an extra line of defense..   also once the port forwards are in place the firewall will ignore / add exceptions for those

Yeah once you are setup with Port Forwards anything coming in the WAN Router on those ports will pass its firewall and just chuck the data to the IP you desire, namely the R600

That should allow the R600 to setup the VPN and all should be good in the world!   And yes the IP should be the 2xx range as you say

Being honest however, once you get this working I would advise breaking it down a bit more.  Setup the the VPN clients on a different subnet and route data between it and LAN as needed, but thats all nicey nicey stuff for later 

Setup the forwards and this should work for ya. 

@Philbert 

Thank you for your response. I removed it from the DMZ and forwarded those ports to the TL-R600VPN at 192.168.0.30 on the LAN and the result is still the same. I've never had problems with forwarding ports on things like web servers or other niche products. I'll keep trying to tinker around with it. If it helps PPTP Pass Through is enabled on the modem/router as well. 

I absolutely agree and will do more hardening on it once I can get it to a working state. Troubleshooting is impossible when you have to change more than one thing and get tangled in a mess of trying to narrow things down. 

I also find it odd how I can't seem to find any references to the ports. I'm not sure what else to troubleshoot as the logs on both the Modem/Router and the TL-R600VPN do not tell me anything. Again, I really appreciate the help. I can't find anything on this.

@Philbert 

Well I've been trying within Lan and outside extensively but I got the occasional ping of death warning but no evidence that any device (Phone or PC) is able to connect to it. I set it to 192.168.0.30 when trying LAN-to-LAN and the WAN address when trying from the internet. I have ports 47 and 1723 forwarded on the main router/modem. At this point I'm all but convinced it's defective. I just don't know how to confirm that.