Apex domains cannot have CNAME records.
Question and response
Question
dig 109.132.213.in-addr.arpa. NS
Answer
109.132.213.in-addr.arpa. 5 NS a.ns.ip-only.net.
109.132.213.in-addr.arpa. 5 NS c.ns.ip-only.net.
109.132.213.in-addr.arpa. 5 NS b.ns.ip-only.net.
Authority
The response has no authority records.
Additional
a.ns.ip-only.net. 4 A 212.112.160.42
b.ns.ip-only.net. 4 A 212.112.163.90
c.ns.ip-only.net. 4 A 83.145.7.217
a.ns.ip-only.net. 4 AAAA 2a01:2b0:1000:2:0:0:0:2
b.ns.ip-only.net. 4 AAAA 2a01:2b0:1000:4:0:0:0:2
c.ns.ip-only.net. 4 AAAA 2a01:2b0:2000:1c6:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0