Okay.
I'm working on a multiplayer game with a VPS as Master Server.
I'll keep a lot of connections opened between the server and each clients in UDP, but I don't want to *really* have a connection between them. The server can take a while before sending the data (so the number of clients waiting can be huge), I just need to keep the router of each client opened to receive it. In my opinion TCP isn't a good alternative.
I usually change the TTL to 3 or 4 maximum so the client's router keep the VPS's ip in its cache but the packet will be deleted quickly before received by the VPS, and any data sent from the Master Server to this router will be rerouted to the local client IP successfully.
It seems to me that TTL modification is pretty used for game network programming. Whether big or small studios.