[Ask] Filter User Hostname Not IP Address via Firewall Rules

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?