Apex domains cannot have CNAME records.
Question and response
Question
dig idris.fr. NS
Answer
idris.fr. 5 NS ciripa.idris.fr.
idris.fr. 5 NS shiva.jussieu.fr.
idris.fr. 5 NS lumiere.idris.fr.
Authority
The response has no authority records.
Additional
shiva.jussieu.fr. 5 A 134.157.0.129
ciripa.idris.fr. 5 A 130.84.32.8
lumiere.idris.fr. 5 A 130.84.8.14
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0