Apex domains cannot have CNAME records.
Question and response
Question
dig crosscert.com. NS
Answer
crosscert.com. 3 NS ns.crosscert.com.
crosscert.com. 3 NS ns3.crosscert.com.
crosscert.com. 3 NS ns2.crosscert.com.
Authority
The response has no authority records.
Additional
ns.crosscert.com. 3 A 211.118.38.95
ns3.crosscert.com. 3 A 211.180.234.215
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0