Apex domains cannot have CNAME records.
Question and response
Question
dig national.inria.fr. NS
Answer
national.inria.fr. 5 NS dns.inria.fr.
national.inria.fr. 5 NS dns-ext2.inria.fr.
Authority
The response has no authority records.
Additional
dns.inria.fr. 5 A 193.51.208.13
dns-ext2.inria.fr. 5 A 193.51.193.133
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0