Apex domains cannot have CNAME records.
Question and response
Question
dig onbmc.com. NS
Answer
onbmc.com. 5 NS pdns203.ultradns.biz.
onbmc.com. 5 NS pdns203.ultradns.net.
onbmc.com. 5 NS pdns203.ultradns.com.
onbmc.com. 5 NS pdns203.ultradns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0