Apex domains cannot have CNAME records.
Question and response
Question
dig exlibrisgroup.com. NS
Answer
exlibrisgroup.com. 5 NS dns2.p04.nsone.net.
exlibrisgroup.com. 5 NS dns4.p04.nsone.net.
exlibrisgroup.com. 5 NS dns1.p04.nsone.net.
exlibrisgroup.com. 5 NS dns3.p04.nsone.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0