Apex domains cannot have CNAME records.
Question and response
Question
dig dsi.cnrs.fr. NS
Answer
dsi.cnrs.fr. 5 NS ns2.cnrs.fr.
dsi.cnrs.fr. 5 NS ns3.cnrs.fr.
dsi.cnrs.fr. 5 NS ns0.cnrs.fr.
Authority
The response has no authority records.
Additional
ns0.cnrs.fr. 5 A 195.220.197.10
ns2.cnrs.fr. 5 A 193.52.36.172
ns3.cnrs.fr. 5 A 193.55.90.12
ns0.cnrs.fr. 5 AAAA 2001:660:500a:2210:0:0:0:10
ns2.cnrs.fr. 5 AAAA 2001:660:500a:2103:0:0:0:10
ns3.cnrs.fr. 5 AAAA 2001:660:6608:5106:0:0:0:12
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0