Apex domains cannot have CNAME records.
Question and response
Question
dig interdomain.org. NS
Answer
interdomain.org. 5 NS ns1.interdomain.net.
interdomain.org. 5 NS ns2.interdomain.net.
interdomain.org. 5 NS ns3.interdomain.es.
Authority
The response has no authority records.
Additional
ns1.interdomain.net. 5 A 217.116.0.206
ns2.interdomain.net. 5 A 86.109.99.246
ns3.interdomain.es. 5 A 217.116.0.208
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0