Apex domains cannot have CNAME records.
Question and response
Question
dig webcas.net. NS
Answer
webcas.net. 4 NS dns1.azia.co.jp.
webcas.net. 4 NS dns.webcas.net.
Authority
The response has no authority records.
Additional
dns.webcas.net. 4 A 115.30.25.251
dns1.azia.co.jp. 4 A 219.101.179.195
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0