HI guys,

Actually when i go to my domain name for example : www.mydomainname.com, it will be transferred to http://my_ip_adresse/mydomainname/

Have i done something wrong on installation, or is it a configuration problem ?

Thanks for helping me out.

Just to give you a little background and why you are being redirected to http://my_ip_adresse/mydomainname/.

Looks like when you installed DNN you installed it using http://my_ip_adresse/mydomainname/.  When DNN looks for the URL in protal aliases, if it cannot find a match it defaults to the first URL that was entered in the list (usually the one used to install DNN).  Therefore if you have not added a new Portal Alias as sebastian describes above, any traffic to the site will default to the first alias in your alias list.

This come in real handy when you have multple domains (mydomain.com, mydomain.net, mydomain.org, etc) and you want the user to always be sent to mydomain.com.  Just setup all the domains to point to the same IP address and enter the mydomain.com as the alias when you install DNN.  Then whenever anyone uses mydomain.net or mydomain.org they will be redirectd to mydomain.com.