drum.violin.co.th has no CNAME records.
Question and response
Question
dig drum.violin.co.th. NS
Answer
The response has no answer records.
Authority
violin.co.th. 480 SOA viola.violin.co.th. nip.symphony.net.th. 1401 180 60 240 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0