Apex domains cannot have CNAME records.
Question and response
Question
dig sm. NS
Answer
sm. 5 NS sm.cctld.authdns.ripe.net.
sm. 5 NS dns.omniway.sm.
sm. 5 NS dns.intelcom.sm.
sm. 5 NS ns3.telecomitalia.sm.
Authority
The response has no authority records.
Additional
dns.omniway.sm. 172600 A 194.183.64.10
dns.intelcom.sm. 172600 A 194.183.64.11
ns3.telecomitalia.sm. 8271 A 194.0.27.12
ns3.telecomitalia.sm. 8271 AAAA 2001:678:28:0:c2:b7:40:12
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0