a.zdnscloud.com has no NS records.
NS records for this zone are defined at zdnscloud.com.
NS records for this zone are defined at zdnscloud.com.
Question and response
Question
dig a.zdnscloud.com. NS
Answer
The response has no answer records.
Authority
zdnscloud.com. 3600 SOA dns1.zdnscloud.info. mail.knet.cn. 1 3600 3600 3600 900
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0