Apex domains cannot have CNAME records.
Question and response
Question
dig KELTIA.NET. NS
Answer
keltia.net. 3 NS ns.frmug.org.
keltia.net. 3 NS ns0.keltia.net.
keltia.net. 3 NS ns1.keltia.net.
keltia.net. 3 NS ns3.keltia.net.
keltia.net. 3 NS cabale.usenet-fr.net.
Authority
The response has no authority records.
Additional
ns.frmug.org. 3 A 213.36.253.97
ns0.keltia.net. 3 A 212.83.129.136
ns1.keltia.net. 3 A 213.36.253.24
ns3.keltia.net. 3 A 108.61.167.174
cabale.usenet-fr.net. 3 A 213.36.253.122
ns.frmug.org. 3 AAAA 2a01:e0d:1:3:58bf:fa61:0:1
ns0.keltia.net. 3 AAAA 2001:470:1f15:53d:1:0:0:4
ns1.keltia.net. 3 AAAA 2001:470:1f15:563:0:0:0:53
ns3.keltia.net. 3 AAAA 2001:19f0:5000:84c2:0:0:0:64
cabale.usenet-fr.net. 3 AAAA 2a01:e0d:1:3:58bf:fa7a:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0