Apex domains cannot have CNAME records.
Question and response
Question
dig es.francetelecom.com. NS
Answer
es.francetelecom.com. 5 NS dns2.wanadoo.es.
es.francetelecom.com. 5 NS dns4.wanadoo.es.
es.francetelecom.com. 5 NS dns1.wanadoo.es.
Authority
The response has no authority records.
Additional
dns1.wanadoo.es. 5 A 62.37.237.140
dns2.wanadoo.es. 5 A 62.37.236.200
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0