Apex domains cannot have CNAME records.
Question and response
Question
dig ipv6dns.se. NS
Answer
ipv6dns.se. 2 NS nsa.interlan.nu.
ipv6dns.se. 2 NS ns1.ipv6dns.se.
ipv6dns.se. 2 NS anycast.interlan.nu.
ipv6dns.se. 2 NS nsu.interlan.nu.
Authority
The response has no authority records.
Additional
ns1.ipv6dns.se. 2 A 192.71.21.35
nsa.interlan.nu. 2 A 194.58.192.46
nsu.interlan.nu. 2 A 185.42.137.98
anycast.interlan.nu. 2 A 194.58.198.32
ns1.ipv6dns.se. 2 AAAA 2001:67c:2448:10:0:0:0:53
nsa.interlan.nu. 2 AAAA 2a01:3f1:46:0:0:0:0:53
nsu.interlan.nu. 2 AAAA 2a01:3f0:400:0:0:0:0:32
anycast.interlan.nu. 2 AAAA 2a01:3f1:3032:0:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0