Apex domains cannot have CNAME records.
Question and response
Question
dig ir. NS
Answer
ir. 5 NS b.nic.ir.
ir. 5 NS a.nic.ir.
ir. 5 NS d.nic.ir.
ir. 5 NS c.nic.ir.
Authority
The response has no authority records.
Additional
a.nic.ir. 155578 A 193.189.123.2
b.nic.ir. 155578 A 193.189.122.83
c.nic.ir. 155578 A 45.93.171.206
d.nic.ir. 155578 A 194.225.70.83
a.nic.ir. 155578 AAAA 2001:678:b0:0:193:189:123:2
b.nic.ir. 155578 AAAA 2001:678:b1:0:193:189:122:83
c.nic.ir. 155578 AAAA 2a0c:6600:4:0:0:0:0:152
d.nic.ir. 155578 AAAA 2001:14e8:c:0:194:225:70:83
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0