Apex domains cannot have CNAME records.
Question and response
Question
dig ipd.brasiltelecom.net.br. NS
Answer
ipd.brasiltelecom.net.br. 5 NS ns01a-cta.brasiltelecom.net.br.
ipd.brasiltelecom.net.br. 5 NS ns02-bsa.brasiltelecom.net.br.
ipd.brasiltelecom.net.br. 5 NS ns01-cta.brasiltelecom.net.br.
ipd.brasiltelecom.net.br. 5 NS ns02a-bsa.brasiltelecom.net.br.
Authority
The response has no authority records.
Additional
ns01-cta.brasiltelecom.net.br. 4 A 201.10.124.18
ns02-bsa.brasiltelecom.net.br. 4 A 201.10.132.18
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0