Why do some sites not open and sometimes redirect to another site?

Question

Computer networks

This is the case, before everything worked fine, the computer and the router itself are not mine. Internet problems began, it was impossible to connect to VK and some services. Messages were sent in telegram and it worked. Took the modem to the provider. Everything worked, but classmates stopped opening on other devices of this wi-fi network (For some reason, the main laptop that is connected to the network is constantly in it, everything is as it should be, everything works fine and everything opens), an error occurs with the correct connection. If you connect from a phone or from another laptop, it does not work, as the site of classmates said, and when connected to some sites, it redirects after loading the page to a site with pornography. It's not the laptop, because yesterday I was setting up a new laptop and could not access the site, because it redirected to another site. As soon as you connect to another wi-fi, everything works fine and does not redirect. I think that the smart modem tuner configured something wrong, the tp-link modem. I still can't enter the modem settings, it just won't connect

Answer 1

1. reset the modem and configure it yourself. see the settings in the contract or check with the provider.
2 dns curves. try to manually register dns on the interface without changing the ip address.

Answer 2

The answer above is most likely correct.
Cant apparently in the router or DNS. Reset and reconfigure.
You can change provider DNS to normal ones directly on your PC or mobile devices.
For example, on such DNS 1.1.1.1 1.0.0.1