Apex domains cannot have CNAME records.
Question and response
Question
dig rockstable.org. NS
Answer
rockstable.org. 5 NS ns4.rockstable.org.
rockstable.org. 5 NS ns3.rockstable.org.
Authority
The response has no authority records.
Additional
ns3.rockstable.org. 5 A 195.201.246.253
ns4.rockstable.org. 5 A 78.47.38.48
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0