Apex domains cannot have CNAME records.
Question and response
Question
dig vtxb.net. NS
Answer
vtxb.net. 4 NS nsd.vtx1.net.
vtxb.net. 4 NS nsb.rgvw.net.
vtxb.net. 4 NS nsg.vtx1.net.
vtxb.net. 4 NS nse.vtx1.net.
vtxb.net. 4 NS nsc.vtx1.net.
vtxb.net. 4 NS nsa.vtx1.net.
vtxb.net. 4 NS nsf.vtx1.net.
vtxb.net. 4 NS nsa.rgvw.net.
vtxb.net. 4 NS nsb.vtx1.net.
vtxb.net. 4 NS ns2.granderiver.net.
vtxb.net. 4 NS bilbo.granderiver.com.
Authority
The response has no authority records.
Additional
nsa.vtx1.net. 4 A 216.183.51.202
nsb.vtx1.net. 4 A 216.183.51.198
bilbo.granderiver.com. 4 A 216.183.32.6
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0