Apex domains cannot have CNAME records.
Question and response
Question
dig vtiger.net. NS
Answer
vtiger.net. 4 NS pdns03.domaincontrol.com.
vtiger.net. 4 NS pdns04.domaincontrol.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0