Apex domains cannot have CNAME records.
Question and response
Question
dig porta.net. NS
Answer
porta.net. 1 NS dns2.porta.net.
porta.net. 1 NS dns1.porta.net.
Authority
The response has no authority records.
Additional
dns1.porta.net. 1 A 200.25.197.196
dns2.porta.net. 1 A 200.25.197.197
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0