Hello,
how can I setup in dns a 301 redirection?
Thank you.

DNS is mostly used to setup network address or mail exchanger records for your domain.
Website redirection can be achieved with an HTTP status code 301, this is a totally different protocol from DNS.
You should use DNS to setup the network address of your website to point to a computer with a web server on it and configure the web server to return HTTP 301 status codes to redirect your site.
Many domain name registrars will do this for you for free, its usually called domain name forwarding.

You can easily do it on your websit like this in Unix:
<?php
header("HTTP/1.1 301 Moved Permanently");
header("Location: http://www.website.com");
exit();
?>

301 For Apache redirect