Tekken 6 Multiplayer Online Without UPNP and DMZ

[AdamN]

DMZ and UPnP is related to Port Forwarding, it allows you to receive incoming data from the internet by forwarding those data from your public IP (ie. the internet) to your LAN IP (and vice versa)
However, even if your router do have UPnP/DMZ/PortForward, your ISP can still blocks incoming data (usually if you're behind NAT/Shared internet connection/mobile data connection)

If you can't port forwards or your ISP blocked it, alternatively, you can use VPN, as VPN is similar to LAN it doesn't need port-forwarding features such as DMZ/UPnP.
But not many VPN have internet access, so you won't be able to use public Adhoc Server (ie. socom.cc) and will need to use built-in AdhocServer, this mean you can only plays with people connected to the same VPN as you (similar to LAN where you can only play with people on the same network)