Apex domains cannot have CNAME records.
Question and response
Question
dig 128-26.203.188.199.in-addr.arpa. NS
Answer
128-26.203.188.199.in-addr.arpa. 5 NS vns2.web-hosting.com.
128-26.203.188.199.in-addr.arpa. 5 NS vns1.web-hosting.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0