Apex domains cannot have CNAME records.
Question and response
Question
dig 1-7.71.134.202.in-addr.arpa. NS
Answer
1-7.71.134.202.in-addr.arpa. 5 NS ns1.corpmart.net.
1-7.71.134.202.in-addr.arpa. 5 NS ns2.corpmart.net.
Authority
The response has no authority records.
Additional
ns1.corpmart.net. 5 A 202.134.71.3
ns2.corpmart.net. 5 A 202.134.71.4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0