When configuring apache or nginx, one of the virtual hosts you configure is the "default" virtual host, used when the Host header didn't match any of the virtua

When configuring apache or nginx, one of the virtual hosts you configure is the "default" virtual host, used when the Host header didn't match any of the virtual hosts. IIRC, on nginx, you explicitly say on the virtual host "this is the default", while on apache, it's either the first or the last (forgot which one). How to configure that virtual host is up to you; the simplest configuration would be to point its document root to an empty directory, and add a couple of access control directives to deny access to it from all IP addresses.