Apex domains cannot have CNAME records.
Question and response
Question
dig theplanet.com. NS
Answer
theplanet.com. 5 NS ns2.theplanet.com.
theplanet.com. 5 NS ns1.softlayer.net.
theplanet.com. 5 NS ns1.theplanet.com.
theplanet.com. 5 NS ns2.softlayer.net.
Authority
The response has no authority records.
Additional
ns1.theplanet.com. 5 A 207.218.247.135
ns2.theplanet.com. 5 A 207.218.223.162
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0