Apex domains cannot have CNAME records.
Question and response
Question
dig inf.spectrum.com. NS
Answer
inf.spectrum.com. 5 NS auth1.charter.com.
inf.spectrum.com. 5 NS auth3.charter.com.
inf.spectrum.com. 5 NS auth2.charter.com.
inf.spectrum.com. 5 NS auth4.charter.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0