dns1.zdnscloud.info has no CNAME records.
Question and response
Question
dig dns1.zdnscloud.info. NS
Answer
The response has no answer records.
Authority
zdnscloud.info. 3600 SOA dns1.zdnscloud.info. mail.knet.cn. 1 3600 3600 3600 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0