Apex domains cannot have CNAME records.
Question and response
Question
dig 128.234.102.101.in-addr.arpa. NS
Answer
128.234.102.101.in-addr.arpa. 5 NS ns01.vips.ne.jp.
128.234.102.101.in-addr.arpa. 5 NS ns00.vips.ne.jp.
128.234.102.101.in-addr.arpa. 5 NS dns.webcas.net.
Authority
The response has no authority records.
Additional
dns.webcas.net. 5 A 115.30.25.251
ns00.vips.ne.jp. 5 A 210.174.191.1
ns01.vips.ne.jp. 5 A 165.76.4.170
ns00.vips.ne.jp. 5 AAAA 2001:278:103b:1:0:0:0:1
ns01.vips.ne.jp. 5 AAAA 2001:278:103c:1:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0