Apex domains cannot have CNAME records.
Question and response
Question
dig 218.36.138.in-addr.arpa. NS
Answer
218.36.138.in-addr.arpa. 5 NS nsauto01.alog.com.br.
218.36.138.in-addr.arpa. 5 NS nsauto02.alog.com.br.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0