primaryns.dnb.com has no CNAME records.
Question and response
Question
dig primaryns.dnb.com. NS
Answer
The response has no answer records.
Authority
dnb.com. 3597 SOA primaryns.dnb.com. dnsadmin.dnb.com. 2021085004 1200 600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0