Apex domains cannot have CNAME records.
Question and response
Question
dig fdn.fr. NS
Answer
fdn.fr. 5 NS soleil.uvsq.fr.
fdn.fr. 5 NS nsa.fdn.org.
fdn.fr. 5 NS gchq.fdn.org.
Authority
The response has no authority records.
Additional
nsa.fdn.org. 5 A 80.67.169.25
gchq.fdn.org. 5 A 80.67.169.26
soleil.uvsq.fr. 4 A 193.51.24.1
nsa.fdn.org. 5 AAAA 2001:910:800:0:0:0:0:25
gchq.fdn.org. 5 AAAA 2001:910:800:0:0:0:0:26
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0