dns51.cloudns.net has no CNAME records.
Question and response
Question
dig dns51.cloudns.net. NS
Answer
The response has no answer records.
Authority
cloudns.net. 508 SOA pns1.cloudns.net. support.cloudns.net. 2026021702 7200 3600 1209600 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0