Apex domains cannot have CNAME records.
Question and response
Question
dig cust.vodafonedsl.it. NS
Answer
cust.vodafonedsl.it. 4 NS ns1.dsl.vodafone.it.
cust.vodafonedsl.it. 4 NS ns2.dsl.vodafone.it.
Authority
The response has no authority records.
Additional
ns1.dsl.vodafone.it. 4 A 91.80.35.143
ns2.dsl.vodafone.it. 4 A 91.80.35.163
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0