Apex domains cannot have CNAME records.
Question and response
Question
dig ipv6.abo.wanadoo.fr. NS
Answer
ipv6.abo.wanadoo.fr. 5 NS ns2.ipv6.orange.fr.
ipv6.abo.wanadoo.fr. 5 NS ns1.ipv6.orange.fr.
Authority
The response has no authority records.
Additional
ns1.ipv6.orange.fr. 3 A 80.10.201.225
ns2.ipv6.orange.fr. 3 A 80.10.202.225
ns1.ipv6.orange.fr. 3 AAAA 2a01:cb04:2040:2:0:0:0:2
ns2.ipv6.orange.fr. 3 AAAA 2a01:cb09:2040:6:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0