Hi  @Ledvedder,

Welcome to the community!

Which operating mode is your Deco X55 in? If it's in router mode, and your gateway is also operating as a router, you may be inadvertently introducing a double NAT scenario, which can cause network anomalies.

If you want to use the Deco X55 as your main router, your gateway should be configured in a "modem-only" operation mode. Depending on your ISP and gateway's hardware, the steps to achieve this configuration may vary.

Alternatively, you can set the Deco X55 in Access Point Mode, allowing your T-Mobile gateway to continue acting as the main router for your network. Please note that some Deco features that require Router Mode will not available in Access Point Mode.

  @Ledvedder 

If you disabled the Wi-Fi on your T-Mobile gateway, but did not take any additional steps to ensure its routing capabilities were disabled (e.g., "bridge mode", "pass-through", or "modem-only" operation), then your T-Mobile gateway may still be acting as another router in your network. 

With both devices acting as routers, a double NAT scenario will be in effect. It sounds like you want the Deco to perform the routing tasks for your network, so I would suggest finding out how you can set your T-Mobile gateway in some form of modem-only operation (if supported). You may be able to find resources in the User Guide or on T-Mobile's website.

Alternatively, you may be able to simpy contact T-Mobile for assistance with the required configuration steps on their device.

If for some reason the T-Mobile gateway doesn't offer bridge mode operation, your options would likely be:

1. Contact T-Mobile to inquire about replacing their gateway with a modem-only device (if possible)

2. Use your T-Mobile gateway as your primary router (with Wi-Fi disabled), and configure the Deco X55 in Access Point Mode instead.