a.spf.163.com has no NS records.
NS records for this zone are defined at 163.com.
NS records for this zone are defined at 163.com.
Question and response
Question
dig a.spf.163.com. NS
Answer
The response has no answer records.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0