Apex domains cannot have CNAME records.
Question and response
Question
dig sbs-inter.net. NS
Answer
sbs-inter.net. 5 NS ns2.sbs-inter.net.
sbs-inter.net. 5 NS ns1-ext.my-it-solutions.net.
sbs-inter.net. 5 NS ns2-ext.my-it-solutions.net.
sbs-inter.net. 5 NS ns1.sbs-inter.net.
Authority
The response has no authority records.
Additional
ns1.sbs-inter.net. 5 A 217.115.72.250
ns2.sbs-inter.net. 5 A 217.115.64.250
ns1-ext.my-it-solutions.net. 5 A 217.115.65.12
ns2-ext.my-it-solutions.net. 5 A 217.115.65.16
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0