Apex domains cannot have CNAME records.
Question and response
Question
dig 0.b.4.1.0.0.a.2.ip6.arpa. NS
Answer
0.b.4.1.0.0.a.2.ip6.arpa. 5 NS p-dns.irz42.net.
0.b.4.1.0.0.a.2.ip6.arpa. 5 NS s-dns.irz42.net.
Authority
The response has no authority records.
Additional
p-dns.irz42.net. 5 A 192.76.134.30
s-dns.irz42.net. 5 A 212.12.50.130
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0