mk.fbnet.com.br has no CNAME records.
Question and response
Question
dig mk.fbnet.com.br. NS
Answer
The response has no answer records.
Authority
fbnet.com.br. 6565 SOA ns1.fbnet.com.br. junior.fbnet.com.br. 1217852253 10800 3600 604800 38400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0