Apex domains cannot have CNAME records.
Question and response
Question
dig clients.easynet.fr. NS
Answer
clients.easynet.fr. 5 NS ns0.easynet.co.uk.
clients.easynet.fr. 5 NS ns.easynet.fr.
Authority
The response has no authority records.
Additional
ns.easynet.fr. 5 A 199.116.149.29
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0