Using a custom /etc/hosts, what IP address should I use to instantly time out? I'm running a web server on localhost

Using a custom /etc/hosts, what IP address should I use to instantly time
out? I'm running a web server on localhost

I was wondering what I should use. I have tried 129.0.0.1 which times out
fairly quickly when I try to access it in a web browser but when loading a
page with ads, there is a significant slowdown.
Using 0.0.0.0 or 127.0.0.1 works well considering I'm running a web server
on localhost. The pages 404 quickly, but that means that I'm getting all
those requests on my server access logs.
I appreciate your time and advice, thanks :).