Disable admin access

I have a network setup that I’d like to move all admin access behind my firewall.

Basically, I want the world to not be able to see mysite.com/wp-admin or wp-login.php as even existing, but internail ip/wp-admin or wp-login.php to work for users behind the firewall on a private IP.

Is this possible? I’ve tried setting up a virtual host on the internal ip and I can get to the site, but it always ends up going out to the publicly available domain.