_spfv6.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 _spfv6.comcast.net. NS
Answer
The response has no answer records.
Authority
comcast.net. 900 SOA dns101.comcast.net. domregtech.comcastonline.com. 2008258643 7200 3600 1209600 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0