Apex domains cannot have CNAME records.
Question and response
Question
dig network.cz. NS
Answer
network.cz. 5 NS trubka.network.cz.
network.cz. 5 NS mamlas.feela.net.
network.cz. 5 NS aerial.network.cz.
Authority
The response has no authority records.
Additional
aerial.network.cz. 5 A 87.236.199.38
mamlas.feela.net. 5 A 217.31.57.209
trubka.network.cz. 5 A 81.91.84.116
aerial.network.cz. 5 AAAA 2a01:5f0:c001:108:2:0:0:1
mamlas.feela.net. 5 AAAA 2001:1ab0:7e1e:d150:0:0:2:100
trubka.network.cz. 5 AAAA 2001:1568:b:0:0:0:0:145
trubka.network.cz. 5 AAAA 2001:1568:b:145:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0