Apex domains cannot have CNAME records.
Question and response
Question
dig vipertec.net.br. NS
Answer
vipertec.net.br. 5 NS b.auto.dns.br.
vipertec.net.br. 5 NS a.auto.dns.br.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0