Apex domains cannot have CNAME records.
Question and response
Question
dig net.yale.edu. NS
Answer
net.yale.edu. 5 NS PKS1302-103.net.yale.edu.
net.yale.edu. 5 NS ns2.bluecatdns.com.
net.yale.edu. 5 NS PKS1302-102.net.yale.edu.
net.yale.edu. 5 NS ns2.bluecatdns.net.
net.yale.edu. 5 NS ns2.bluecatdns.org.
Authority
The response has no authority records.
Additional
pks1302-102.net.yale.edu. 5 A 128.36.72.27
pks1302-103.net.yale.edu. 5 A 128.36.72.29
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0