ns4.mainloop.net has no NS records.
NS records for this zone are defined at mainloop.net.
NS records for this zone are defined at mainloop.net.
Question and response
Question
dig ns4.mainloop.net. NS
Answer
The response has no answer records.
Authority
mainloop.net. 600 SOA ns1.mainloop.net. hostmaster.mainloop.net. 3959 600 100 604800 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0