Apex domains cannot have CNAME records.
Question and response
Question
dig ent.cust.swisscom.ch. NS
Answer
ent.cust.swisscom.ch. 5 NS ns11.scs-ns.ch.
ent.cust.swisscom.ch. 5 NS ns12.scs-ns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0