Apex domains cannot have CNAME records.
Question and response
Question
dig gslb.hk.net. NS
Answer
gslb.hk.net. 4 NS gslbns2.hk.net.
gslb.hk.net. 4 NS gslbns1.hk.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0