Apex domains cannot have CNAME records.
Question and response
Question
dig 87.34.192.in-addr.arpa. NS
Answer
87.34.192.in-addr.arpa. 4 NS ns-b.axcelx.net.
87.34.192.in-addr.arpa. 4 NS ns-a.axcelx.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0