Apex domains cannot have CNAME records.
Question and response
Question
dig ultradns.org. NS
Answer
ultradns.org. 5 NS pdns196.ultradns.info.
ultradns.org. 5 NS ns61.ultradns2.com.
ultradns.org. 5 NS pdns196.ultradns.net.
ultradns.org. 5 NS pdns196.ultradns.com.
ultradns.org. 5 NS ns61.ultradns2.org.
ultradns.org. 5 NS pdns196.ultradns.co.uk.
ultradns.org. 5 NS pdns196.ultradns.biz.
ultradns.org. 5 NS pdns196.ultradns.org.
Authority
The response has no authority records.
Additional
pdns196.ultradns.org. 5 A 156.154.67.196
pdns196.ultradns.org. 5 AAAA 2001:502:4612:0:0:0:0:e8
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0