Apex domains cannot have CNAME records.
Question and response
Question
dig dsl.telesp.net.br. NS
Answer
dsl.telesp.net.br. 5 NS dnsqipbr2.telesp.net.br.
dsl.telesp.net.br. 5 NS dnsqipbr1.telesp.net.br.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0