When you have several domains with different extensions and you need all of them to open exactly the same site, you could have the website under one of them and forward all the rest. There are several methods to redirect one domain to another, including the so-called domain parking. When your hosting package allows it, though, it will be better if you host all the domains and set up a URL redirect, not a domain redirect. The difference between the two is that while a domain name is hosted, you may still have content for it, create subdomains, e-mail addresses, and so forth., while with a parked domain it's not possible to do any of these things. For instance, if you are building localized sites under several country-code Internet domain names, you'll be able to work on them, but in the meantime, visitors shall be redirected to the primary website.