Apex domains cannot have CNAME records.
Question and response
Question
dig luadns.net. NS
Answer
luadns.net. 5 NS ns2.luadns.net.
luadns.net. 5 NS ns1.luadns.net.
luadns.net. 5 NS ns4.luadns.net.
luadns.net. 5 NS ns3.luadns.net.
Authority
The response has no authority records.
Additional
ns1.luadns.net. 5 A 185.142.218.1
ns2.luadns.net. 5 A 185.142.218.2
ns3.luadns.net. 5 A 185.142.218.3
ns4.luadns.net. 5 A 185.142.218.4
ns1.luadns.net. 5 AAAA 2001:67c:25a0:0:0:0:0:1
ns2.luadns.net. 5 AAAA 2001:67c:25a0:0:0:0:0:2
ns3.luadns.net. 5 AAAA 2001:67c:25a0:0:0:0:0:3
ns4.luadns.net. 5 AAAA 2001:67c:25a0:0:0:0:0:4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0