dns2.gvt.net.br has no NS records.
NS records for this zone are defined at gvt.net.br.
NS records for this zone are defined at gvt.net.br.
Question and response
Question
dig dns2.gvt.net.br. NS
Answer
The response has no answer records.
Authority
gvt.net.br. 86400 SOA dns1.gvt.net.br. operacao.gvt.net.br. 329 28800 14400 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0