Apex domains cannot have CNAME records.
Question and response
Question
dig 58.4.in-addr.arpa. NS
Answer
58.4.in-addr.arpa. 5 NS dnsauth2.sys.gtei.net.
58.4.in-addr.arpa. 5 NS dnsauth1.sys.gtei.net.
58.4.in-addr.arpa. 5 NS dnsauth3.sys.gtei.net.
Authority
The response has no authority records.
Additional
dnsauth1.sys.gtei.net. 5 A 4.2.49.2
dnsauth2.sys.gtei.net. 5 A 4.2.49.3
dnsauth3.sys.gtei.net. 5 A 4.2.49.4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0