Phone not automatically connecting to 5g internet

Near as I can tell, memorized characteristics of the older Wi-Fi network, even with the same SSID, are getting in the way of connecting to the same named SSID on the new Gateway. Go figure.

The second thing I figured out, eventually, was that the more elderly of the two wi-fi connected printers I was running was simply incompatible with the same named SSID. No amount of mucking with the printer settings worked. Found a hint on the web: The 5G Wi-Fi band signals, as generated by the 5G gateway, were not compatible with the 5G Wi-Fi on the printer. Some kind of backward compatibility problem. Solution was odd, but workable: Using the 5G Gateway App, created Yet Another SSID, a single character off from the main SSID I was using. Again in the App, rig it so that SSID is on the 2.5G Wi-Fi band, only. Give it a random but sane password and configure the Gateway.

That worked: The printer connected to the 2.5G Wi-Fi sans problems and was able to print.

One Last Thing. So, in this place, pre-T-Mobile-Gateway, I was running a Cable Modem; output of the cable modem was wired to the WAN port of a Netgear Nighthawk. That's a dual-band (5G/2.5G) Wi-Fi router with four Ethernet ports. Half the gear in the house ran from Wi-Fi; the other half was hard-wired to 1GbE Ethernet, RJ45 and all; and there was a small  $15-dollar-special Access Point in the garage that provided some Wi-Fi coverage for some gear that needed it, hooked up to one of those Ethernet cables.

First mistake: Removing the WAN cable from the Cable Modem and putting the Ethernet cable from the 5G Gateway in its place. Um. That Won't Work Well. Turns out that t-mobile is doing Carrier-Grade NAT; and the router was also doing NAT, resulting in everything in the house having to go through two stages of NAT to get to the Greater Internet. If you look up this kind of configuration on the Interwebs, you get shifty looking eyeballs from the cognescenti. It's kind of.. well, it ought to work. But there are reports out there that, well, "working" is a relative term. And I can report that I saw weird behavior.

Solution: One can continue to use a router in this kind of configuration, but the best thing to do is to put the router in Access Point mode. When one does this, it turns off the router's NAT (which is OK, the T-Mobile Gateway will do the job) and the router's DHCP server.. which is also fine, the 5G Gateway will do the job there, too. Further, as I said above, that Gateway runs IPV6, natively: And, after the change-over, suddenly, everything in the house has a bunch of IPV6 addresses as well as some "backup" IPV4 addresses.. and everything starts working Much Better.

You’re welcome.