Apex domains cannot have CNAME records.
Question and response
Question
dig ultradnstools.com. NS
Answer
ultradnstools.com. 5 NS pdns196.ultradns.org.
ultradnstools.com. 5 NS pdns196.ultradns.co.uk.
ultradnstools.com. 5 NS pdns196.ultradns.com.
ultradnstools.com. 5 NS pdns196.ultradns.biz.
ultradnstools.com. 5 NS pdns196.ultradns.net.
ultradnstools.com. 5 NS pdns196.ultradns.info.
Authority
The response has no authority records.
Additional
pdns196.ultradns.biz. 5 A 156.154.66.196
pdns196.ultradns.com. 5 A 156.154.64.196
pdns196.ultradns.net. 5 A 156.154.65.196
pdns196.ultradns.biz. 5 AAAA 2610:a1:1015:0:0:0:0:e8
pdns196.ultradns.com. 5 AAAA 2001:502:f3ff:0:0:0:0:e8
pdns196.ultradns.net. 5 AAAA 2610:a1:1014:0:0:0:0:e8
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0