This thread may perhaps be of interest to you. It isn't a solved solution yet from the looks of things but it should get you on the right path. The fact that you already have Open NAT on both consoles is a start.
Thanks for the info smith, I'm not going to be able to try any of this until next week cuz I'm going out of town, but if I can get it to work somehow, I'll post it here and on the thread you gave me.
Which MI424WR router (revision number)?
What firmware version is installed on the router?
How do you get internet (Coax or Ethernet)?
Which MI424WR router (revision number)? MI424WR-GEN2 F
What firmware version is installed on the router? 20.19.8
How do you get internet (Coax or Ethernet)? Coax
I hope that's what you need
I have the same problem as you. Two Xboxes on the same router, both with Open NAT. We can play online multiplayer at the same time, just not in the same game/match.
I have the Rev E version of the router, but it is very similar to your Rev F. In fact, both run the same firmware. I too have 20.19.8 installed. And my internet is delivered via Coax.
The only way to get multiple Xboxes to party-up and play in the same game/match is to enable Universal Plug and Play (UPnP). You do not want to use static IPs with your Xboxes, since UPnP requires non-static IP address assignments in order to work.
To be honest I got this to work once, but the next time we partied-up, it again would not let us in the same match. Either it is an issue with the router, the firmware or I did something to hose the configuration. I've been away so I have not had time to mess with it. However, a buddy is coming over this weekend and we will try to recreate the success we had earlier.
In the meantime I offer this...
1) Before you do anything else, make sure to save your current router configuration to a file.
2) Make sure Universal Plug and Play is enabled (has a check in the box). This is under the Advanced link on main page.
3) Be sure DMZ is not enabled (no check in box). This is under the Firewall Settings link on main page.
4) Be sure there are no static IP's defined for the Xboxes on your router.
5) On the Xboxes, their network configurations are set to automatic (and not manual) so the router will assign an IP address.
6) Reboot the router (I prefer to turn it off for a couple of minutes, then turn it back on versus using the Reboot router link).
7) Fire-up the Xboxes and give it a try.
If that does not work, you might take a look at the Port Forwarding Rules (under the Advanced link, on the main page). When set to Basic, all you see are a dozen or so port forwarding rules. If you click on Advanced, you will see page after page of port forwarding rules, including many for games and one for Xbox. In my earlier testing, things only worked well if I selected the Advanced link (with page after page of entries). It seems the rules displayed when you leave the Port Forwarding Rules page are the rules applied. And, UPnP failed miserably when only the Basic rules were displayed. Seems UPnP may depend on the rules defined.
The other setting you might try is the Firewall level. I had set mine to Low and that worked for me that one time.
Good luck. I will provide any update from our testing this weekend, if it is helpful.
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