Apex domains cannot have CNAME records.
Question and response
Question
dig 226.167.195.in-addr.arpa. NS
Answer
226.167.195.in-addr.arpa. 3 NS nsrev00.dns.sfr.net.
226.167.195.in-addr.arpa. 3 NS nsrev01.dns.sfr.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0