Apex domains cannot have CNAME records.
Question and response
Question
dig 192-26.246.65.83.in-addr.arpa. NS
Answer
192-26.246.65.83.in-addr.arpa. 5 NS ns3.futureweb.at.
192-26.246.65.83.in-addr.arpa. 5 NS ns2.futureweb.at.
192-26.246.65.83.in-addr.arpa. 5 NS ns1.futureweb.at.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0