Apex domains cannot have CNAME records.
Question and response
Question
dig ul.ie. NS
Answer
ul.ie. 5 NS hermes.ul.ie.
ul.ie. 5 NS auth-ns2.heanet.ie.
ul.ie. 5 NS mercury.ul.ie.
ul.ie. 5 NS auth-ns3.heanet.ie.
Authority
The response has no authority records.
Additional
hermes.ul.ie. 5 A 193.1.100.131
mercury.ul.ie. 5 A 193.1.100.130
auth-ns2.heanet.ie. 5 A 193.1.247.198
auth-ns3.heanet.ie. 5 A 5.196.22.225
auth-ns2.heanet.ie. 5 AAAA 2001:770:1c:4:0:0:c101:f7c6
auth-ns3.heanet.ie. 5 AAAA 2001:41d0:52:900:0:0:0:871
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0