WordPress.org

I want to display a custom message before sending the user to the login page

Create a html page not managed by WP and redirect the user to the page, enter the message on the page and create a link to the login page.

Can I enter hostnames instead of IP adresses?

No this is not supported yet, however it will be in future releases.

What do you use this plugin for?

I use it to control access to my blog from my corporate proxys as I dont want all my collegues to look at my blog without my knowledge.