Apex domains cannot have CNAME records.
Question and response
Question
dig forth.gr. NS
Answer
forth.gr. 3 NS dns1.ics.forth.gr.
forth.gr. 3 NS grdns-at.ics.forth.gr.
forth.gr. 3 NS grdns.ics.forth.gr.
forth.gr. 3 NS estia.ics.forth.gr.
forth.gr. 3 NS gr-d.ics.forth.gr.
forth.gr. 3 NS gr-c.ics.forth.gr.
Authority
The response has no authority records.
Additional
gr-c.ics.forth.gr. 167680 A 194.0.1.25
gr-d.ics.forth.gr. 172798 A 194.0.11.102
estia.ics.forth.gr. 172011 A 139.91.191.3
grdns.ics.forth.gr. 167680 A 139.91.1.1
gr-c.ics.forth.gr. 167680 AAAA 2001:678:4:0:0:0:0:19
gr-d.ics.forth.gr. 172798 AAAA 2001:678:e:102:0:0:0:53
estia.ics.forth.gr. 172011 AAAA 2001:648:2c30:0:0:0:191:3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0