ns-643.awsdns-16.net has no NS records.
NS records for this zone are defined at awsdns-16.net.
NS records for this zone are defined at awsdns-16.net.
Question and response
Question
dig ns-643.awsdns-16.net. NS
Answer
The response has no answer records.
Authority
awsdns-16.net. 900 SOA g-ns-465.awsdns-16.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0