Apex domains cannot have CNAME records.
Question and response
Question
dig digitalinsight.com. NS
Answer
digitalinsight.com. 5 NS edns123.ultradns.net.
digitalinsight.com. 5 NS edns123.ultradns.org.
digitalinsight.com. 5 NS edns123.ultradns.biz.
digitalinsight.com. 5 NS edns123.ultradns.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0