Ya I hope we can bring more visibility to this issue, as it's seen with other router Mfrs and not just ASUS.
I this may affect 3rd party FW along with OEM FW.
I believe there are several levels and problems that are a factor in gaining OPEN NAT with two or more game consoles being online at the same time.
1. ISP and Home NAT configuration. We assume that the ISP modem doesn't have NAT and the ASUS router or any external router is the only NAT. This is recommended and preferred for gaming environments. Also wired LAN cable is preferred over wireless and wireless can present various problems and speed issues which can effect in gaming performances.
2. Design of routers NAT, QoS and uPnP and the logic code and handling of gaming consoles and data traffic are more directed towards single game consoles and may not be flexible to handle more than one game console since the average home over the years usually has 1 game console. This may present a limitation on the Mfr router due to its implementation and design of it's UI and it's features. Some router Mfrs use a one IP address per port in there UI, where other router Mfrs may let users input a range of IP addresses in the UI. D-Link is one where there QoS feature seen on older generation routers, users can input Local and Remote IP address range along with a range of port numbers to use. This configuration with the use of uPnP seems to allow two or more game consoles to report OPEN NAT while online with out using any Port Forwarding configurations.
3. Port usage is a factor as in the Xbox Live example mentioned, port 3074 is the main service game port for all XBL games. Only one port can be accessed per device when online so port 3074 is given to single game console when online. This is standard networking and port policy. However if two or more devices are online at the same time and needing to use the same port, if uPnP is enabled on the router, and it's design and configuration is done right, uPnP and the router can use a Virtual port to connect the 2nd device to the gaming service, thus giving same service and NAT condition to the 2nd device, i.e. game console while online at the same time with the first. Ports 3075 thru 3078 have been seen and or mentioned in other forum and online articles.
I have done and seen this with 3 XB1s connected to a DIR-655 Rev B using the following configuration:
http://forums.dlink.com/index.php?topic=42011.0
BO3 was the game being played on all 3 consoles.
4. I believe that game console network status and in game network status for NAT conditions may differ depending on networking logic and is handling of any network condition they encounter due to many and various networks seen in the home. I've seen were the Xbox dash board reads OPEN NAT, while the in game NAT status reports Moderate or Strict NAT. i.e. BO3. Not sure which method is correct or weather one or the other network status app is less accurate or more accurate than the other. Things have changed since the XB1 came out with NAT status feature while the older 360 console didn't have this feature and everyone relied on the in game NAT status feature for information. I also remember having two 360s connected and gaming on MW3 and BO2 and both consoles having OPEN NAT.
5. Port usage is also depending upon which game console gets turned on first. First one gets 3074. After that, who knows. Some routers have a "route status" feature that reports IP addresses and ports being used per device. This can be help in seeing what ports are being used by each game console. I have seen 3075 and 3076 being used as well.
My 2 cents!
I would recommend trying the following:
Need to disable "Instant ON" on the XB1 and test. This feature was known to cause bad NAT status behavior in the beginning and I haven't seen any information if it's been corrected or not.
Test Scenario:
Enable uPnP only and set IP address reservations for each game console. Don't set up any Port Forwarding rules. Be sure consoles are OFF.
Turn on the 1st game console and check dash board NAT condition then check in game NAT condition.
Turn off the 1st game console and turn on the 2nd game console and check both NAT conditions. This may show uPnP handling performances of the ports and connections and NAT status may or may not be OPEN on both.
Turn OFF the 2nd game console.
Turn ON the 1st game console and check both NAT status. Leave ON.
Turn ON the 2nd game console and check both NAT status. This may show uPnP handling performances of the ports and connections and both NAT status may or may not be OPEN on both.
Test Scenario:
Enable upnp and set IP address reservations for each game console. Be sure consoles are OFF.
Set up QoS rules for the 1st and 2nd game console and see if QoS and uPnP can help with OPEN NAT.
Turn ON the 1st game console and check both NAT status. Leave ON.
Turn ON the 2nd game console and check both NAT status. This may show QoS and uPnP handling performances of the ports and connections and NAT status may or may not be OPEN on both.
Test Scenario:
Disable uPnP and set IP address reservations for each game console. Be sure consoles are OFF.
Set up Port Forwarding or Port Range Trigger rules for the 1st and 2nd game console and see if Port Forwarding can help with OPEN NAT. Configure Port 3074 for 1st game console and 3075 or 3076 or 3077 or 3078 for the 2nd game console.
Turn ON the 1st game console and check both NAT status. Leave ON.
Turn ON the 2nd game console and check both NAT status. This may show Port Forwarding/Triggering handling performances of the ports and connections and NAT status may or may not be OPEN on both.
During any of these test case scenarios, a router reboot maybe needed to clear and flush uPnP and port tables. I might do a reboot after saving the router configuration before turning on the 1st game console.
