Apex domains cannot have CNAME records.
Question and response
Question
dig 234.102.101.in-addr.arpa. NS
Answer
234.102.101.in-addr.arpa. 4 NS ns1.iprevolution.co.jp.
234.102.101.in-addr.arpa. 4 NS rns2.softbankbb.jp.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0