Apex domains cannot have CNAME records.
Question and response
Question
dig cornell.edu. NS
Answer
cornell.edu. 4 NS bigred.cit.cornell.edu.
cornell.edu. 4 NS drdns.cit.cornell.edu.
cornell.edu. 4 NS drdns2.cit.cornell.edu.
cornell.edu. 4 NS cudns.cit.cornell.edu.
cornell.edu. 4 NS dns.cit.cornell.edu.
Authority
The response has no authority records.
Additional
dns.cit.cornell.edu. 4 A 192.35.82.53
cudns.cit.cornell.edu. 4 A 132.236.56.252
drdns.cit.cornell.edu. 4 A 52.152.185.125
bigred.cit.cornell.edu. 4 A 128.253.180.35
drdns2.cit.cornell.edu. 4 A 52.45.47.12
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0