How to configure a default domain
A default domain can best be configured on the server side. This can be achieved by inserting a Rewriterule in the .htaccess file, which forces the website to be loaded on 1 prominent domain name. It's also possible to place a redirect in the application server.
To ensure a solid implementation of the default domain, an HTTP 301 (Moved Permanently) is recommended. This makes it clear to the search engine indexing robots that the referring domain is also the prominent domain name.
It is not recommended to place an http 302 (Moved Temporarlily), because this leaves the impression that the prominent domain name is only a temporary event.