After reading this it appears your ethernet port might be after some router in that basement. So placing a router after a router is sometimes trying.
Try this next setup instead. Use your router as a WAP. Google this:
"How to use a router as a WAP?"
In short, I would not use the WAN port of my router for a test setup.
**Model**: Netgear R6100|AC1200 Dual Band Router
**Firmware**: 22.214.171.124 when the problem started, but I manually updated to 126.96.36.199
**ISP**: AT&T supplied via ethernet port by our apartment building -- the way I understand it, they have a modem in the basement that routes internet to each apartment's ethernet port.
**Error message**: "Cannot connect to DNS server" (or a variation of that, depending on the browser or device used to connect to the router via WiFi or ethernet.) Also, on the home page of the "basic" tab of the router settings page, it recognizes that there is no internet connection.
**Devices**: Troubleshooting mainly from Intel NUC5i3RYK w/ Samsung 850 EVO 120 GB M.2 3.5-Inch SSD and Crucial CT2CP25664BF160B 4GB ram kit. Also tried with my 2013 MacBook Air 13".
**Devices connected**: At highest usage (which is rare) we have two desktops connected via ethernet, two laptops via wireless, two phones via wireless, one tablet via wireless, one printer via wireless, and one smart tv via wireless. Usually, however, we don't have more than 5 connected at once.
**Other notables**: Our property managers say that only one other person has reported internet problems, and he also has a Netgear router. Everyone else's seems to be working fine. The property managers havn't changed anything concerning the modem or fiddled with anything.
**What I've tried so far, in order**:
1. Check to see if internet issues are present on both bands, on all wireless and wired devices. They are. Each wireless device connects to the wifi but has no internet connection.
2. Turned off all antivirus on all my devices to see if it helped. It didn't.
3. Checked the logs. The router seems to be connecting and disconnecting to the internet continuously.
4. Power cycle router, and while I'm at it, reseat all ethernet and power cords in the back of the router and the wall. No dice.
5. Plug ethernet cable from wall directly into desktop, to see if it's my problem or the ISP. The internet works fine (currently using this method right now.)
6. Try using the automatic internet troubleshooting thing provided by the router settings page. Didn't work, as usual.
7. Download latest firmware using desktop ethernet connection, then connect to router and upload and install. I now have updated firmware, but still no internet.
8. Try using Google's DNS service instead of the one automatically provided by my ISP. Nope.
9. Tried to spoof the router's mac address with my desktop's mac address. (pretty much shooting in the dark at this point.) No difference.
10. Factory reset the router. Still didn't work.
11. Tried setting the router as an AP. Finally was able to access the internet, but at laughably slow speeds. For some reason it wanted to use my MacBook's IP. Promptly set it back, since I've had it set up as a regular router and it's worked great for months until it suddenly didn't.
Please help! I'm tech saavy enough but networking is not my specialty. I've exhausted all of my troubleshooting knowledge.