developer-ext.Level3.com has no CNAME records.
Question and response
Question
dig developer-ext.Level3.com. NS
Answer
The response has no answer records.
Authority
Level3.com. 3516 SOA ns2.Level3.net. dns.level3.net. 2025102309 7200 600 2592000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0