ns2.cdnsun.net has no CNAME records.
Question and response
Question
dig ns2.cdnsun.net. NS
Answer
The response has no answer records.
Authority
cdnsun.net. 180 SOA cdnsun.net. hostmaster.worldcdn.com. 1772275105 1200 180 1209600 180
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0