Apex domains cannot have CNAME records.
Question and response
Question
dig net.vodafone.it. NS
Answer
net.vodafone.it. 5 NS nsmob3.net.vodafone.it.
net.vodafone.it. 5 NS nsmob2.net.vodafone.it.
net.vodafone.it. 5 NS nsmob1.net.vodafone.it.
Authority
The response has no authority records.
Additional
nsmob1.net.vodafone.it. 5 A 91.81.133.2
nsmob2.net.vodafone.it. 5 A 91.81.133.3
nsmob3.net.vodafone.it. 5 A 91.81.133.10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0