ns6.blacknight.com has no CNAME records.
Question and response
Question
dig ns6.blacknight.com. NS
Answer
The response has no answer records.
Authority
blacknight.com. 1453 SOA ns1.blacknight.com. hostmaster.blacknight.com. 1276183966 14400 7200 2419200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0