one could also forward all traffic using NAT, to go to a specific IP.
Use a dstnat rule, to forward all ip addresses except one that you don’t use, to a specific ip address. on port 80
That way any website requested using port 80 would redirect to your selected web page, this would however not allow any other connections on port 80, so if you have connections on your network that allows internet traffic, they too will be redirected to the selected ip.
So no connections on port 80 except to designated server.
Web proxy is the easiest way.
Forbid all, and redirect to… what you want.
The redirect works if you have a specific web server, that can be accessed by it’s ip (it’s the only server on that ip, or it’s de default virtual server on an apache installation, for example. ), and you do the NAT redirects on the router