Apex domains cannot have CNAME records.
Question and response
Question
dig interserver.net. NS
Answer
interserver.net. 5 NS ns200.interserver.net.
interserver.net. 5 NS ns300.interserver.net.
interserver.net. 5 NS ns100.interserver.net.
Authority
The response has no authority records.
Additional
ns100.interserver.net. 5 A 162.159.8.245
ns200.interserver.net. 5 A 162.159.9.154
ns300.interserver.net. 5 A 162.159.10.165
ns100.interserver.net. 5 AAAA 2400:cb00:2049:1:0:0:a29f:8f5
ns200.interserver.net. 5 AAAA 2400:cb00:2049:1:0:0:a29f:99a
ns300.interserver.net. 5 AAAA 2400:cb00:2049:1:0:0:a29f:aa5
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0