Apex domains cannot have CNAME records.
Question and response
Question
dig chi-mct.il.static.cable.rcncustomer.com. NS
Answer
chi-mct.il.static.cable.rcncustomer.com. 2 NS auth2.dns.rcn.net.
chi-mct.il.static.cable.rcncustomer.com. 2 NS auth4.dns.rcn.net.
chi-mct.il.static.cable.rcncustomer.com. 2 NS auth1.dns.rcn.net.
chi-mct.il.static.cable.rcncustomer.com. 2 NS auth3.dns.rcn.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0