said by DaveX510 :Ya both xboxs need ports 3074 etc otherwise one always one will have a strict nat and trouble connecting or staying connected. MY wife and I both play and most games dont allow split screening on ranked matches even if we wanted to. I had read here and other places (1-3 years) old about getting 4 additional IPs for like 10 a month thats why I was asking. So I guess my options are dsl or an additional modem/account.
Well, if the Upnp option does not work, and if it is something that you will be doing a lot, maybe the option of a self-built router with 3 NIC's in it would work for you. One of the NIC's is connected directly to your cable modem, the 2nd would be your internal lan (Desktops, Laptops, etc) with all the correct rules and ports being blocked. The third, would really be a "wide open connection" to the internet, with no ports being blocked. Put a 8 port switch in there, and then connect your two (or 3, or 5) xbox's to that. That way, no ports need to be opened or traffic forwarded to specific IP's on the other side of your router. It will all be passed though.
Again, that would be a lot of extra work and setup, but from what I read, it could be done with Smoothwall Express. I believe Moonwall or PFSense would do the same thing, but not sure.
However, I do somewhat remember an issue with one of these game systems (don't remember which one), but if you did connect two or more behind a router, the 2nd would never connect, as they both had the same public IP. There was some rule in the game servers that if they saw multiple connections to the game from the same public IP, only one would be allowed in. If that's the case here, then yes you would need multiple public IP's. Again, that was a number of years ago, and I don't remember the game system or the specific game that had that issue. But, I do remember a very long discussion about that.
Edit: Wanted to add a link to a news item that was posted by RyanC6
back on 05/07/2012 that references what I was talking about (separate network on a home-built router for gaming). See the section "Orange Interface" for more information on this
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Securing Your Home Network Utilizing Multiple Network Interfaces [0] comments--Brian