166.unused.bb.bigbytesystems.com has no CNAME records.
Question and response
Question
dig 166.unused.bb.bigbytesystems.com. NS
Answer
The response has no answer records.
Authority
bigbytesystems.com. 3582 SOA ns01.bigbytesystems.com. admin.mail.bigbytesystems.com. 2022083005 7200 7200 2419200 345600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0