Apex domains cannot have CNAME records.
Question and response
Question
dig cloud.zayo.com. NS
Answer
cloud.zayo.com. 5 NS ns20.zayo.com.
cloud.zayo.com. 5 NS ns10.zayo.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0