Apex domains cannot have CNAME records.
Question and response
Question
dig isp.net. NS
Answer
isp.net. 5 NS gate.lasvegas.net.
isp.net. 5 NS gremlin.lasvegas.net.
Authority
The response has no authority records.
Additional
gate.lasvegas.net. 5 A 64.250.224.2
gremlin.lasvegas.net. 5 A 64.250.224.6
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0