Apex domains cannot have CNAME records.
Question and response
Question
dig ns3.tanhost.com. NS
Answer
ns3.tanhost.com. 5 NS ns1.tanhost.com.
ns3.tanhost.com. 5 NS ns2.tanhost.com.
ns3.tanhost.com. 5 NS ns3.tanhost.com.
Authority
The response has no authority records.
Additional
ns1.tanhost.com. 3 A 199.204.72.169
ns2.tanhost.com. 3 A 109.72.149.111
ns3.tanhost.com. 3 A 171.25.204.169
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0