Apex domains cannot have CNAME records.
Question and response
Question
dig interhost.it. NS
Answer
interhost.it. 5 NS ns2.dnsitalia.net.
interhost.it. 5 NS nsct.dnsitalia.net.
interhost.it. 5 NS nsrm.dnsitalia.net.
interhost.it. 5 NS ns1.dnsitalia.net.
Authority
The response has no authority records.
Additional
ns1.dnsitalia.net. 5 A 194.242.61.66
ns2.dnsitalia.net. 5 A 151.11.50.4
nsct.dnsitalia.net. 5 A 52.29.120.99
nsrm.dnsitalia.net. 5 A 151.11.52.66
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0