Apex domains cannot have CNAME records.
Question and response
Question
dig 128-25.55.112.212.in-addr.arpa. NS
Answer
128-25.55.112.212.in-addr.arpa. 5 NS ns1.itsystem.se.
128-25.55.112.212.in-addr.arpa. 5 NS ns2.itsystem.se.
Authority
The response has no authority records.
Additional
ns1.itsystem.se. 5 A 212.112.55.234
ns2.itsystem.se. 5 A 83.172.111.59
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0