mx2a1.comcast.net has no NS records.
NS records for this zone are defined at comcast.net.
NS records for this zone are defined at comcast.net.
Question and response
Question
dig mx2a1.comcast.net. NS
Answer
The response has no answer records.
Authority
comcast.net. 900 SOA dns101.comcast.net. domregtech.comcastonline.com. 2008258639 7200 3600 1209600 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0