ns7.customer.Level3.net has no CNAME records.
Question and response
Question
dig ns7.customer.Level3.net. NS
Answer
The response has no answer records.
Authority
customer.level3.net. 95 SOA ns1.Level3.net. dns.level3.net. 2019010900 7200 600 2592000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0