Redirect from external URLs

I want to use the maintenance page designed and stored at `<internal-IP>/maintenance-page/` as the target URL for multiple other URLs to use as a common web portal maintenance page. 

E.g. my-website.com -> `<internal-IP>/maintenance-page/`
       my-other-website.com -> `<internal-IP>/maintenance-page/` and so on. 

How to do this?

