Apex domains cannot have CNAME records.
Question and response
Question
dig itop.net.br. NS
Answer
itop.net.br. 5 NS autoritativo02.itop.net.br.
itop.net.br. 5 NS autoritativo01.itop.net.br.
Authority
The response has no authority records.
Additional
autoritativo01.itop.net.br. 5 A 192.140.88.23
autoritativo02.itop.net.br. 5 A 192.140.88.27
autoritativo01.itop.net.br. 5 AAAA 2804:3d34:0:0:0:0:0:33
autoritativo02.itop.net.br. 5 AAAA 2804:3d34:0:0:0:0:0:34
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0