Apex domains cannot have CNAME records.
Question and response
Question
dig exchange. NS
Answer
exchange. 5 NS v0n2.nic.exchange.
exchange. 5 NS v0n0.nic.exchange.
exchange. 5 NS v2n0.nic.exchange.
exchange. 5 NS v2n1.nic.exchange.
exchange. 5 NS v0n1.nic.exchange.
exchange. 5 NS v0n3.nic.exchange.
Authority
The response has no authority records.
Additional
v0n0.nic.exchange. 172200 A 65.22.28.14
v0n1.nic.exchange. 172200 A 65.22.29.14
v0n2.nic.exchange. 172200 A 65.22.30.14
v0n3.nic.exchange. 172200 A 161.232.14.14
v2n0.nic.exchange. 172200 A 65.22.31.14
v2n1.nic.exchange. 172200 A 161.232.15.14
v0n0.nic.exchange. 172200 AAAA 2a01:8840:1e:0:0:0:0:14
v0n1.nic.exchange. 172200 AAAA 2a01:8840:1f:0:0:0:0:14
v0n2.nic.exchange. 172200 AAAA 2a01:8840:20:0:0:0:0:14
v0n3.nic.exchange. 172200 AAAA 2a01:8840:f8:0:0:0:0:14
v2n0.nic.exchange. 172200 AAAA 2a01:8840:21:0:0:0:0:14
v2n1.nic.exchange. 172200 AAAA 2a01:8840:f9:0:0:0:0:14
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0