Apex domains cannot have CNAME records.
Question and response
Question
dig portailmunicipal.net. NS
Answer
portailmunicipal.net. 5 NS motorhead.easydns.org.
portailmunicipal.net. 5 NS rush.easydns.com.
portailmunicipal.net. 5 NS nirvana.easydns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0