Apex domains cannot have CNAME records.
Question and response
Question
dig rrpproxy.net. NS
Answer
rrpproxy.net. 5 NS pdns109.ultradns.biz.
rrpproxy.net. 5 NS pdns109.ultradns.net.
rrpproxy.net. 5 NS pdns109.ultradns.com.
rrpproxy.net. 5 NS pdns109.ultradns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0