Apex domains cannot have CNAME records.
Question and response
Question
dig gslb.lightedge.com. NS
Answer
gslb.lightedge.com. 5 NS ns2.lightedge.com.
gslb.lightedge.com. 5 NS ns1.lightedge.com.
gslb.lightedge.com. 5 NS ns3.lightedge.com.
Authority
The response has no authority records.
Additional
ns1.lightedge.com. 5 A 216.81.191.225
ns2.lightedge.com. 5 A 64.247.222.1
ns3.lightedge.com. 5 A 216.182.182.17
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0