ns4.blacknight.com has no NS records.
NS records for this zone are defined at blacknight.com.
NS records for this zone are defined at blacknight.com.
Question and response
Question
dig ns4.blacknight.com. NS
Answer
The response has no answer records.
Authority
blacknight.com. 3600 SOA ns1.blacknight.com. hostmaster.blacknight.com. 1276184929 14400 7200 2419200 3600
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0