Apex domains cannot have CNAME records.
Question and response
Question
dig rivnet.com. NS
Answer
rivnet.com. 5 NS nsg.vtx1.net.
rivnet.com. 5 NS nse.vtx1.net.
rivnet.com. 5 NS bilbo.granderiver.com.
rivnet.com. 5 NS ns2.granderiver.com.
rivnet.com. 5 NS nsc.vtx1.net.
rivnet.com. 5 NS nsa.vtx1.net.
rivnet.com. 5 NS nsd.vtx1.net.
rivnet.com. 5 NS nsf.vtx1.net.
rivnet.com. 5 NS nsb.vtx1.net.
Authority
The response has no authority records.
Additional
ns2.granderiver.com. 5 A 216.183.32.7
bilbo.granderiver.com. 5 A 216.183.32.6
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0