Apex domains cannot have CNAME records.
Question and response
Question
dig impervadns.net. NS
Answer
impervadns.net. 5 NS ns2.impervadns.net.
impervadns.net. 5 NS ns3.impervadns.net.
impervadns.net. 5 NS ns1.impervadns.net.
Authority
The response has no authority records.
Additional
ns1.impervadns.net. 5 A 198.143.61.64
ns1.impervadns.net. 5 A 198.143.61.65
ns1.impervadns.net. 5 A 198.143.61.66
ns1.impervadns.net. 5 A 198.143.61.164
ns1.impervadns.net. 5 A 198.143.61.165
ns1.impervadns.net. 5 A 198.143.61.166
ns2.impervadns.net. 5 A 198.143.62.64
ns2.impervadns.net. 5 A 198.143.62.65
ns2.impervadns.net. 5 A 198.143.62.66
ns2.impervadns.net. 5 A 198.143.62.164
ns2.impervadns.net. 5 A 198.143.62.165
ns2.impervadns.net. 5 A 198.143.62.166
ns3.impervadns.net. 5 A 198.143.63.64
ns3.impervadns.net. 5 A 198.143.63.65
ns3.impervadns.net. 5 A 198.143.63.66
ns3.impervadns.net. 5 A 198.143.63.164
ns3.impervadns.net. 5 A 198.143.63.165
ns3.impervadns.net. 5 A 198.143.63.166
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0