Apex domains cannot have CNAME records.
Question and response
Question
dig zeus.unixbsd.info. NS
Answer
zeus.unixbsd.info. 5 NS ns2.unixbsd.info.
zeus.unixbsd.info. 5 NS ns3.unixbsd.info.
Authority
The response has no authority records.
Additional
ns2.unixbsd.info. 1 A 208.87.243.238
ns3.unixbsd.info. 1 A 74.117.57.121
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0