Apex domains cannot have CNAME records.
Question and response
Question
dig 128.54.121.27.in-addr.arpa. NS
Answer
128.54.121.27.in-addr.arpa. 5 NS ns002-3n3fpt6phv8cl6s1.3.d-53.jp.
128.54.121.27.in-addr.arpa. 5 NS ns002-3n3fpt6phv8cl6s1.3.d-53.net.
128.54.121.27.in-addr.arpa. 5 NS ns002-3n3fpt6phv8cl6s1.3.d-53.info.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0