dns5.istweb.com.br has no CNAME records.
Question and response
Question
dig dns5.istweb.com.br. NS
Answer
The response has no answer records.
Authority
istweb.com.br. 10800 SOA ns280.hostgator.com.br. root.br280.hostgator.com.br. 2026013101 86400 7200 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0