Apex domains cannot have CNAME records.
Question and response
Question
dig secondary.se. NS
Answer
secondary.se. 5 NS ns.cafax.se.
secondary.se. 5 NS primary.se.
secondary.se. 5 NS secondary.se.
Authority
The response has no authority records.
Additional
ns.cafax.se. 5 A 192.71.228.17
primary.se. 5 A 192.36.115.53
secondary.se. 5 A 63.34.32.172
ns.cafax.se. 5 AAAA 2001:6b0:302:0:0:0:0:17
primary.se. 5 AAAA 2a01:298:4:0:0:0:0:53
secondary.se. 5 AAAA 2a05:d018:184:4853:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0