CNAME not works

[elbawdy]

Hi,
I try to create CNAME called "cdn.mp3down.co" > "mp3down.co",
But when I try to go to the CANME it's redirects me to the main domain why?
mp3down.co is addon domain on my main domain.

http://www.diigo.com/item/image/gmfw/advi

Regards.