Apex domains cannot have CNAME records.
Question and response
Question
dig ihszimbra.com. NS
Answer
ihszimbra.com. 5 NS dijkstra.ihsdns.com.
ihszimbra.com. 5 NS knuth.ihsdns.com.
Authority
The response has no authority records.
Additional
knuth.ihsdns.com. 3 A 94.138.196.9
dijkstra.ihsdns.com. 3 A 167.172.166.241
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0