Moderate NAT issue wont resolve. "Your network is behind a port-restricted NAT"

Alrighty, first off apologies in advance if this is posted in the wrong spot.

I have an issue with moderate NAT type on both my brother's Xbox 1 and my own. We have a gateway modem Segem F@st 1704 and Windstream is out ISP. My brother's Xbox is wired into this gateway. I have a line from the gateway up to a wireless router in my room,
it is a D-link 4500 Gamerlounge. I am unable to bridgemode the gateway with my router do to not have access to the PPoE information needed for that, which makes that out of the question to try (unfortunately).My Xbox sits on a separate network on my router
than my brother who is on the network within the gateway.

I feel like I have tried everything under the sun to get both consoles in open NAT type. From clearing the UPNP tables and power cycling. Putting my Xbox in DMZ mode on my router, opening ports and forwarding ports in all sorts of directions (one at a time
of course) on both the gateway and the router.

The only issue that brings me here to solve the Moderate NAT type issue is I am unable to join games and voice chat with my brother. (I will use GTA online as an example) I can join his game on GTA but no one else can. I can be in a game with a third person
but if my brother tries to join he cant join and I get booted from the game and visa versa. I can be in a party with him and other people but not in games. Which lead me to try and solve this NAT issue. We tried being on the same network, on the two different
networks and nothing seems to help. Is it the hardware? ISP? a setting? or is the problem on the Xbox's themselves?

Thank you to anyone who reads through that and attempts to help.

:)

 

Port forwarding question

I have discovered why my X1 reports a Strict or Moderate NAT sometimes and it's after one of the 360s uses one of the ports the X1 needs. As soon as a Live port is used for a 360 via UPnP, 3074 for example, the X1 drops to Strict.

This is exactly the reason why I use UPnP, because if 360 1 is using 3074, UPnP will map 360 2 to a different port number that grants the same access as 3074 allowing both to communicate with the Live service at the same time, thus granting an Open NAT to all connected 360s. The X1 is not triggering port forwarding via UPnP to utilise this feature, so is the device that suffers when a 360 is in use.

The PS3 used to have a UPnP enable/disable option on the console itself, which I thought was odd, but perhaps if the 360 had this, enabling it would tell the console to use UPnP, which once it uses UPnP to trigger the ports I'm sure it will resolve the multiple device issue.

For reference:

• When I have an Open NAT, the X1's Detailed NAT Information says: Your network is behind a cone NAT
• When I have a Moderate NAT, the X1's Detailed NAT Information says: Your network is behind a port-restricted NAT
• When I have a Strict NAT, the X1's Detailed NAT Information says: Your network is behind a port-preserving port-symmetric NAT

 

Changing NAT type

"Your network is behind a port-restricted NAT"

How do I change this from Moderate to Open?

 

About the only way to get open NAT on 2 consoles is to have a good gaming router that does UPNP , your "Gateway" is most likely causing double nat ...if you cant get it in "bridge mode" you MAY have some luck ... , you may have to get a new modem (no gateway
, modem only)