backend.bbtel.com has no NS records.
NS records for this zone are defined at bbtel.com.
NS records for this zone are defined at bbtel.com.
Question and response
Question
dig backend.bbtel.com. NS
Answer
The response has no answer records.
Authority
bbtel.com. 3600 SOA ns1.bbtel.com. adminblue.bbtel.com. 520800125 1200 180 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0