Apex domains cannot have CNAME records.
Question and response
Question
dig 80-87.44.9.213.in-addr.arpa. NS
Answer
80-87.44.9.213.in-addr.arpa. 5 NS frigg.dnsnodes.com.
80-87.44.9.213.in-addr.arpa. 5 NS odin.dnsnodes.eu.
80-87.44.9.213.in-addr.arpa. 5 NS thor.dnsnodes.eu.
Authority
The response has no authority records.
Additional
odin.dnsnodes.eu. 5 A 213.9.14.107
thor.dnsnodes.eu. 5 A 217.79.214.253
frigg.dnsnodes.com. 5 A 217.79.214.245
odin.dnsnodes.eu. 5 AAAA 2a02:4c00:0:8000:0:0:0:5
thor.dnsnodes.eu. 5 AAAA 2a02:20a8:a000:4:0:0:0:53
frigg.dnsnodes.com. 5 AAAA 2a02:20a8:a000:4:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0