Apex domains cannot have CNAME records.
Question and response
Question
dig ufrj.br. NS
Answer
ufrj.br. 5 NS ns.ufrj.br.
ufrj.br. 5 NS nsx.ufrj.br.
Authority
The response has no authority records.
Additional
ns.ufrj.br. 5 A 146.164.170.11
nsx.ufrj.br. 5 A 200.156.137.11
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0