dns103.comcast.net has no CNAME records.
Question and response
Question
dig dns103.comcast.net. NS
Answer
The response has no answer records.
Authority
comcast.net. 115 SOA dns101.comcast.net. domregtech.comcastonline.com. 2008258655 7200 3600 1209600 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0