Apex domains cannot have CNAME records.
Question and response
Question
dig 128.5.61.in-addr.arpa. NS
Answer
128.5.61.in-addr.arpa. 5 NS ns1.cyber.net.pk.
128.5.61.in-addr.arpa. 5 NS ns5.cyber.net.pk.
128.5.61.in-addr.arpa. 5 NS ns4.cyber.net.pk.
128.5.61.in-addr.arpa. 5 NS ns.cyber.net.pk.
128.5.61.in-addr.arpa. 5 NS ns2.cyber.net.pk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0