dns1.cvnet.com has no NS records.
NS records for this zone are defined at cvnet.com.
NS records for this zone are defined at cvnet.com.
Question and response
Question
dig dns1.cvnet.com. NS
Answer
The response has no answer records.
Authority
cvnet.com. 900 SOA authns1.cv.net. abuse.cv.net. 2013126505 7200 600 604800 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0