Apex domains cannot have CNAME records.
Question and response
Question
dig 129.84.62.in-addr.arpa. NS
Answer
129.84.62.in-addr.arpa. 5 NS ns.sbone.cz.
129.84.62.in-addr.arpa. 5 NS ns2.sbone.cz.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0