Apex domains cannot have CNAME records.
Question and response
Question
dig o2switch.fr. NS
Answer
o2switch.fr. 4 NS vador.o2sdns.fr.
o2switch.fr. 4 NS dark.o2sdns.fr.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0