Apex domains cannot have CNAME records.
Question and response
Question
dig daum.net. NS
Answer
daum.net. 4 NS ns1.daum.net.
daum.net. 4 NS ns2.daum.net.
Authority
The response has no authority records.
Additional
ns1.daum.net. 4 A 113.61.106.5
ns2.daum.net. 4 A 113.61.107.5
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0