Apex domains cannot have CNAME records.
Question and response
Question
dig vtr.net. NS
Answer
vtr.net. 5 NS ns00.vtr.net.
vtr.net. 5 NS ns01.vtr.net.
Authority
The response has no authority records.
Additional
ns00.vtr.net. 5 A 200.104.255.130
ns01.vtr.net. 5 A 200.74.121.200
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0