ns1.customer.Level3.net has no CNAME records.
Question and response
Question
dig ns1.customer.Level3.net. NS
Answer
The response has no answer records.
Authority
customer.level3.net. 1692 SOA ns1.Level3.net. dns.level3.net. 2019010900 7200 600 2592000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0