spf-b.rnmk.com has no NS records.
NS records for this zone are defined at rnmk.com.
NS records for this zone are defined at rnmk.com.
Question and response
Question
dig spf-b.rnmk.com. NS
Answer
The response has no answer records.
Authority
rnmk.com. 900 SOA dnsmasterac01.rightnowtech.com. root.rightnowtech.com. 1772476944 600 180 1209600 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0