play online on android with a router/jouer en ligne sur android via un modem

[nc50lc]

Nope, it's not the IP. It is just the default gateway for most routers.
If you Type that is a browser's URL Box, you'll be directed to the router's set-up. (different set-up per account: basic and advanced)

Have you tried connecting without enabling DMZ?
I think PPSSPP can connect without it. Just make sure you have a friend/buddy to play with for testing. (must be connected to different routers)