New Router = Can't Find RN424 drives

First log into the admin web ui of the NAS and navigate to the network page.  Click on the settings wheel next to the graphic.  (There will be more than one graphic, the one you want is the one that is not grayed out).

There will be a pop-up with three tabs at the top.  Pick the one that says IPv4 (which is in the center).  If the configure field doesn't say "Using DHCP" then  set it to that.  Then power down the NAS using the power control in the upper right of the web page..

Then you can switch routers.  After the switch, power up the NAS.  After it boots, you should be able to see its new IPv4 address on the LCD panel.  Make a note of that address.  It will most likely be different than the IP address you were using with the old router.

You can go into the tmobile gateway settings, and reserve that address for the NAS, so it will always get that IP address every time the system restarts.  (Best to download the gateway manual and look for that setting).

Then try opening Windows File Explorer and enter \\NAS-IP-ADDRESS (using the actual address you noted above, instead of the NAS-IP-ADDRESS placeholder).  You will need likely to enter your NAS user credentials again.   See if that opens up your list of shares, and confirm that you can access them.

Since the IP address will be different, you will need to re-do the mapped drives on the PC(s).

Thank you for the quick and succinct reply.

At present, I have no way of logging into the T-Mobile Gateway's admin interface. Although the product label indicates an admin IP address (192.168.12.1) and a password, when I attempt to access it, all I see is a high level status page (e.g. signal strength) with the IP address in the browser bar changed to 192.168.1.1.

I have no idea on what features that the admin interface may even present. There is no printed manual available online, as far as I can tell.

I had consulted T-Mobile technical assistance and even made it is as far as a supervisor, explaining that I needed to access the admin interface, and she filed a "ticket" to obtain that information and promised to get back to me on the following evening, and that was two nights ago. I'll contact them shortly when I have an hour or so to see what the status of that request is.

The T-Mobile Gateway is a TMO-G4AR. The app that you reference is the "T-Life" app which provides access to rudimentary parental controls and the ability to hide the wifi SSID, but that's all. The T-Life app is what I used to set up the gateway, which included naming my wifi network and its password.

The label that indicates the model also indicates the admin IP address and the password, but try as I might, I am never prompted for these.

I doubt that I am the first person to try to use the T-Mobile internet on a wired network with a NAS. T-Mobile has been offering "5G" home wireless internet for several years.

I haven't been able to find HinT. Also, do I really need RAIDar? My RN424 can display its IP address on its front display. But, I will certainly install it if I need it.

I have other switches in this network, but they are all unmanaged: two Netgear GS116's and one GS105. The RN424 is connected to the same switch as my existing router, to which I attempted to connect the T-Mobile gateway resulting in my "losing" the network drive.

I tried connecting the T-Mobile gateway to the WAN port on my existing ancient router, leaving the router LAN connections as they are, but I had no wired access to the internet as a result. However, after some research, I have discovered that I may have to reboot the router and NAS when I change WANs, which I have not tried yet.

I have been having other network problems and will get back to this shortly. I appreciate the help you have given me so far and will get back to this in a few days.