Apex domains cannot have CNAME records.
Question and response
Question
dig centos-server.net. NS
Answer
centos-server.net. 2 NS ns1.wolverinedns.com.
centos-server.net. 2 NS ns3.wolverinedns.com.
centos-server.net. 2 NS ns2.wolverinedns.com.
centos-server.net. 2 NS ns4.wolverinedns.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0