Apex domains cannot have CNAME records.
Question and response
Question
dig xundns.com. NS
Answer
xundns.com. 5 NS u1.xundns.com.
xundns.com. 5 NS u2.xundns.com.
Authority
The response has no authority records.
Additional
u1.xundns.com. 5 A 61.163.30.167
u1.xundns.com. 5 A 103.236.55.23
u1.xundns.com. 5 A 111.6.96.28
u1.xundns.com. 5 A 113.137.46.32
u1.xundns.com. 5 A 117.50.200.252
u1.xundns.com. 5 A 218.95.37.77
u2.xundns.com. 5 A 38.114.114.238
u2.xundns.com. 5 A 42.236.74.175
u2.xundns.com. 5 A 111.6.188.201
u2.xundns.com. 5 A 122.114.44.16
u2.xundns.com. 5 A 222.186.169.209
u1.xundns.com. 5 AAAA 2408:8722:1801:10:4:611:6303:167
u1.xundns.com. 5 AAAA 2409:8c44:1b00:601:1:1110:609:6028
u1.xundns.com. 5 AAAA 240e:bf:b800:4300:0:2:1:8
u1.xundns.com. 5 AAAA 240e:cf:9000:13:0:0:0:17
u1.xundns.com. 5 AAAA 240e:95d:3020:1e:0:0:0:52
u2.xundns.com. 5 AAAA 2408:8621:0:42:e401:402:0:9
u2.xundns.com. 5 AAAA 2408:8621:0:42:e401:413:0:11
u2.xundns.com. 5 AAAA 2408:8720:806:204:0:0:0:24
u2.xundns.com. 5 AAAA 240e:e9:a805:0:0:1:0:3
u2.xundns.com. 5 AAAA 2604:86c0:2001:6:0:0:2672:72ee
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0