ns4.nic.co.com has no NS records.
NS records for this zone are defined at nic.co.com.
NS records for this zone are defined at nic.co.com.
Question and response
Question
dig ns4.nic.co.com. NS
Answer
The response has no answer records.
Authority
nic.co.com. 3600 SOA ns0.centralnic-dns.com. hostmaster.centralnic-dns.com. 1507729839 300 300 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0