Apex domains cannot have CNAME records.
Question and response
Question
dig inet-addr.com. NS
Answer
inet-addr.com. 4 NS ns3.plusserver.com.
inet-addr.com. 4 NS ns2.plusserver.com.
inet-addr.com. 4 NS ns1.plusserver.com.
Authority
The response has no authority records.
Additional
ns1.plusserver.com. 4 A 62.138.233.183
ns2.plusserver.com. 4 A 62.138.201.123
ns3.plusserver.com. 4 A 18.158.102.90
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0