Apex domains cannot have CNAME records.
Question and response
Question
dig ipser.net. NS
Answer
ipser.net. 4 NS ns.ipser.net.
ipser.net. 4 NS ns.sigmasoft.com.
Authority
The response has no authority records.
Additional
ns.ipser.net. 4 A 168.235.85.6
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0