Apex domains cannot have CNAME records.
Question and response
Question
dig impervasecuredns.net. NS
Answer
impervasecuredns.net. 5 NS ns7.impervasecuredns.net.
impervasecuredns.net. 5 NS ns5.impervasecuredns.net.
impervasecuredns.net. 5 NS ns6.impervasecuredns.net.
impervasecuredns.net. 5 NS ns13.impervasecuredns.net.
impervasecuredns.net. 5 NS ns2.impervasecuredns.net.
impervasecuredns.net. 5 NS ns9.impervasecuredns.net.
impervasecuredns.net. 5 NS ns8.impervasecuredns.net.
impervasecuredns.net. 5 NS ns11.impervasecuredns.net.
impervasecuredns.net. 5 NS ns4.impervasecuredns.net.
impervasecuredns.net. 5 NS ns3.impervasecuredns.net.
impervasecuredns.net. 5 NS ns1.impervasecuredns.net.
impervasecuredns.net. 5 NS ns10.impervasecuredns.net.
impervasecuredns.net. 5 NS ns12.impervasecuredns.net.
Authority
The response has no authority records.
Additional
ns1.impervasecuredns.net. 5 A 192.230.121.1
ns2.impervasecuredns.net. 5 A 192.230.122.1
ns3.impervasecuredns.net. 5 A 192.230.123.1
ns4.impervasecuredns.net. 5 A 192.230.121.4
ns5.impervasecuredns.net. 5 A 192.230.122.4
ns6.impervasecuredns.net. 5 A 192.230.123.4
ns7.impervasecuredns.net. 5 A 192.230.121.7
ns8.impervasecuredns.net. 5 A 192.230.122.7
ns9.impervasecuredns.net. 5 A 192.230.123.7
ns10.impervasecuredns.net. 5 A 192.230.121.10
ns11.impervasecuredns.net. 5 A 192.230.122.10
ns12.impervasecuredns.net. 5 A 192.230.123.10
ns13.impervasecuredns.net. 5 A 192.230.121.13
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0