Apex domains cannot have CNAME records.
Question and response
Question
dig eduroam.fr. NS
Answer
eduroam.fr. 3 NS dns-3.dfn.de.
eduroam.fr. 3 NS ns2.renater.fr.
eduroam.fr. 3 NS resone.univ-rennes1.fr.
eduroam.fr. 3 NS ns1.u-strasbg.fr.
eduroam.fr. 3 NS ns1.renater.fr.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0