Apex domains cannot have CNAME records.
Question and response
Question
dig fiber.net. NS
Answer
fiber.net. 2 NS ns4.fiber.net.
fiber.net. 2 NS ns3.fiber.net.
fiber.net. 2 NS ns1.fiber.net.
fiber.net. 2 NS ns2.fiber.net.
Authority
The response has no authority records.
Additional
ns1.fiber.net. 2 A 216.83.130.2
ns2.fiber.net. 2 A 216.83.130.7
ns3.fiber.net. 2 A 69.160.64.2
ns4.fiber.net. 2 A 69.168.67.2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0