DNS hijacking
EDIT: So because of my $0 budget and the fact that my uptime is around 50% (PC, no additional servers) I ended up using NextDNS. For the time being it works (according to dnsleaktest), an added benefit was improved ad-blocking (100% in this tool). I now have plans for a proper router in the future with a Pi-hole. Thanks so much for all the info & suggestions, definitely learnt a lot.
So it turns out I got myself into an ISP that was shittier than expected (I already knew it was kinda shitty), they DNS hijack for whatever reason and I can't manually set my own DNS on my router or even my devices.
Cyber security has never been my forte but I'm always trying to keep learning as I go. I've read that common solutions involve using a different port (54) or getting a different modem/router or just adding a router.
Are they all true? Whats the cheapest, easiest way of dealing with all of this?
I can, they get redirected to my ISPs DNS, no matter what. This was not an issue with my pervious company.
How are you detecting this? Just curiosity
Often, if you try to go to a non-existent domain, it'll still return an IP address that loads a "this site doesn't exist" page hosted by the ISP, often full of sponsored links, similar to a domain parking page.
It's trivial to do this. DNS requests are unencrypted and can easily be modified by an ISP, even if you use a custom DNS server like Google's 8.8.8.8 or Cloudflare's 1.1.1.1. You need DNS over HTTPS or a similar technology to prevent this happening.
hijacking dns is also my provider's first action when you're late paying the bill. by ip or doh or a long-lived dns cache and you're still going, but anything looked-up via a 'regular' dns server goes nowhere. that gets you another 2-3 weeks until they deny the modem from even authenticating.