When I go to iknowwhatyoudownload.com, a bunch of stuff shows up for my IP that’s definitely not being downloaded by anyone in my house (foreign language torrents). Aside from that my router (AT&T Arris BGW210) needs to be restarted about once a week, due to some kind of dhcp issue. The most recent event seemed bad - none of my devices had internet, they could all talk to each other, and my ONT activity light was flickering steadily. During this time I had no access to the router, even plugged in directly to LAN. Fixed by a restart but no idea what was going on.
The DHT torrent thing has been happening for months and the router thing could just be that AT&T sucks. I have no other evidence that something is wrong.
I could buy a firewall and put it downstream of the AT&T equipment.
I could switch internet providers, get a new IP address and router, and see if that fixes it.
Should I try to figure out what’s going on or just keep restarting the router once a week and ignore the DHT hits from my static IP?
I don’t think they use CG-NAT my IP starts with 75, and it hasn’t changed in years.
75.0.0.0/8 is the ARIN range for commercial businesses. Just because it's outside of the 100.0.0.0/8 range doesn't mean it isn't an address held by a NAT. If I remember correctly it's used by either Comcast or Charter, both of which will put you behind a NAT unless you are paying for a static IP on a business account (and you mentioned you aren't)
AT&T fiber, through a reseller so it is a commercial account.
Not necessarily the same thing, it could easily be a small leased block using NAT to offer service to more customers in that case. The reseller has a commercial account, yes, but that doesn't mean you get exclusive access to an address in that block (very unlikely unless you are dropping big money.) Nothing you have said so far rules out being behind a NAT.