Output: Array

[0] => l.o.n.g.s.u.b.d.o.m.a.i.n

[1] => ddomainn

[2] => net

<?php
function parse_domain($domain)
{
    $p1 = strrpos($domain, '.');
    $p2 = strrpos($domain, '.', (strlen($domain) - $p1 + 1) * -1);
    return array(substr($domain, 0, $p2), substr($domain, $p2 + 1, $p1 - $p2 - 1), substr($domain, $p1 + 1));
}
$domain = parse_domain("l.o.n.g.s.u.b.d.o.m.a.i.n.ddomainn.net");
print_r($domain);
// or for urls...
$domain = parse_url("http://l.o.n.g.s.u.b.d.o.m.a.i.n.ddomainn.net/index.php?key=val", PHP_URL_HOST)
$domain = parse_domain($domain);
print_r($domain);
?>