Apex domains cannot have CNAME records.
Question and response
Question
dig nsserve.net. NS
Answer
nsserve.net. 5 NS ns0.nsserve.net.
nsserve.net. 5 NS ns1.nsserve.net.
nsserve.net. 5 NS ns2.nsserve.net.
Authority
The response has no authority records.
Additional
ns0.nsserve.net. 5 A 52.56.103.87
ns1.nsserve.net. 5 A 194.1.164.168
ns2.nsserve.net. 5 A 194.1.164.167
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0