Apex domains cannot have CNAME records.
Question and response
Question
dig c.ovd.interhost.com. NS
Answer
c.ovd.interhost.com. 5 NS ns4.interhost.com.
c.ovd.interhost.com. 5 NS ns.interhost.com.
c.ovd.interhost.com. 5 NS ns2.interhost.com.
c.ovd.interhost.com. 5 NS ns3.interhost.com.
Authority
The response has no authority records.
Additional
ns.interhost.com. 5 A 213.134.33.70
ns2.interhost.com. 5 A 213.134.32.170
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0