Apex domains cannot have CNAME records.
Question and response
Question
dig site24x7.eu. NS
Answer
site24x7.eu. 4 NS pdns90.ultradns.biz.
site24x7.eu. 4 NS NS31.ZNS-53.COM.
site24x7.eu. 4 NS ns1.zohocorp.com.
site24x7.eu. 4 NS NS11.ZNS-53.COM.
site24x7.eu. 4 NS NS21.ZNS-53.NET.
site24x7.eu. 4 NS NS41.ZNS-53.NET.
site24x7.eu. 4 NS pdns90.ultradns.net.
site24x7.eu. 4 NS pdns90.ultradns.com.
Authority
The response has no authority records.
Additional
ns1.zohocorp.com. 4 A 156.154.67.90
ns11.zns-53.com. 4 A 136.143.172.88
ns21.zns-53.net. 4 A 136.143.173.99
ns31.zns-53.com. 4 A 169.148.151.88
ns41.zns-53.net. 4 A 169.148.152.99
ns1.zohocorp.com. 4 AAAA 2001:502:4612:0:0:0:0:7e
ns11.zns-53.com. 4 AAAA 2602:801:c00a:0:0:0:0:88
ns21.zns-53.net. 4 AAAA 2602:801:c00b:0:0:0:0:99
ns31.zns-53.com. 4 AAAA 2602:801:c00c:0:0:0:0:88
ns41.zns-53.net. 4 AAAA 2602:801:c00c:0:0:0:0:99
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0