How to make a certain site open first when using a cheap router?

Question

Computer networks

There are several DLink DIR-620 routers in different parts of the city, all receive Internet from different providers. How to make clients connecting to them automatically see a certain resource as the first site? Like the one done by MosMetro, or Megafon (mobile Internet) - an authorization mini-page that does not require anything, just click "continue". Perhaps this is called HotSpot, but there is no such task here, authorization is not necessary, the page is opened only for information.
1) I don’t know the revisions yet, but if the 620s are flashable, then you can try OpenWRT. An inconvenient option, because. will have to suffer and ride a lot
2) Do you have your own cloud resources, perhaps raise your own DNS and make it give the address I need in response to the first requests? Then the clients will start having problems in the DNS cache? Those. gave DNS to the request ya.ru some of my 1.2.3.4 page, then every time a person tries to go to ya.ru will get to 1.2.3.4 instead of Yandex?

Answer 1

What you want to do is called the Captive portal, I'll give you just a couple of links, then I think you'll figure it out.
habrahabr.ru/sandbox/79059
wiki.openwrt.org/doc/howto/wireless.overview