Apex domains cannot have CNAME records.
Question and response
Question
dig ddos-guard.net. NS
Answer
ddos-guard.net. 5 NS ns2.ddos-guard.net.
ddos-guard.net. 5 NS ns4.ddos-guard.net.
ddos-guard.net. 5 NS ns1.ddos-guard.net.
ddos-guard.net. 5 NS ns5.ddos-guard.net.
ddos-guard.net. 5 NS ns6.ddos-guard.net.
ddos-guard.net. 5 NS ns3.ddos-guard.net.
Authority
The response has no authority records.
Additional
ns1.ddos-guard.net. 5 A 186.2.170.100
ns2.ddos-guard.net. 5 A 185.129.100.200
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0