Apex domains cannot have CNAME records.
Question and response
Question
dig cust.lidnet.se. NS
Answer
cust.lidnet.se. 5 NS ns.lidnet.net.
cust.lidnet.se. 5 NS ns3.lidnet.net.
cust.lidnet.se. 5 NS ns2.lidnet.net.
cust.lidnet.se. 5 NS ns4.lidnet.net.
Authority
The response has no authority records.
Additional
ns.lidnet.net. 3 A 212.112.34.10
ns2.lidnet.net. 3 A 212.112.32.210
ns3.lidnet.net. 3 A 212.112.34.23
ns4.lidnet.net. 3 A 212.112.34.24
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0