Apex domains cannot have CNAME records.
Question and response
Question
dig dynu.com. NS
Answer
dynu.com. 4 NS ns6.dynu.com.
dynu.com. 4 NS ns5.dynu.com.
dynu.com. 4 NS ns4.dynu.com.
dynu.com. 4 NS ns3.dynu.com.
dynu.com. 4 NS ns1.dynu.com.
dynu.com. 4 NS ns2.dynu.com.
dynu.com. 4 NS ns0.dynu.com.
Authority
The response has no authority records.
Additional
ns0.dynu.com. 4 A 66.85.159.14
ns1.dynu.com. 4 A 72.51.58.2
ns2.dynu.com. 4 A 108.181.13.234
ns3.dynu.com. 4 A 162.251.164.146
ns4.dynu.com. 4 A 108.181.159.122
ns5.dynu.com. 4 A 216.105.169.98
ns6.dynu.com. 4 A 173.0.55.138
ns2.dynu.com. 4 AAAA 2602:ff23:0:8888:0:0:0:2
ns3.dynu.com. 4 AAAA 2605:9f80:4000:214:0:0:0:2
ns4.dynu.com. 4 AAAA 2604:6600:2000:39:0:0:0:2
ns5.dynu.com. 4 AAAA 2605:9f80:c000:404:0:0:0:2
ns6.dynu.com. 4 AAAA 2607:f8f8:631:8612:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0