Apex domains cannot have CNAME records.
Question and response
Question
dig posten-salgsnett.el-fa.net. NS
Answer
posten-salgsnett.el-fa.net. 5 NS dns102.registrar-servers.com.
posten-salgsnett.el-fa.net. 5 NS dns101.registrar-servers.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0