ns03.webex.com has no CNAME records.
Question and response
Question
dig ns03.webex.com. NS
Answer
The response has no answer records.
Authority
webex.com. 120 SOA hns001.sjc03.webex.com. csg-ia.cisco.com. 2023903133 10800 1800 2419200 120
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0