Apex domains cannot have CNAME records.
Question and response
Question
dig pracase.sfr.fr. NS
Answer
pracase.sfr.fr. 5 NS ns2pub.sfr.fr.
pracase.sfr.fr. 5 NS ns1pub.sfr.fr.
Authority
The response has no authority records.
Additional
ns1pub.sfr.fr. 5 A 92.90.26.129
ns2pub.sfr.fr. 5 A 92.90.26.145
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0