external.servercentral.com has no CNAME records.
Question and response
Question
dig external.servercentral.com. NS
Answer
The response has no answer records.
Authority
servercentral.com. 591 SOA ns1.servercentral.net. dns.servercentral.net. 2025110302 600 600 600 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0