I want to filter access to my site’s login page using the hostname from the ISP rather than the IP Address. But I don’t know how to do it. Can Cloudflare firewall do that?
I am afraid it cant. What you are asking for is a reverse lookup and at best you could do this in the context of a worker, however you are likely to run into the time constraints and furthermore delay all of your requests.
Why cant you block by IP?