billing.bul.net has no NS records.
NS records for this zone are defined at bul.net.
NS records for this zone are defined at bul.net.
Question and response
Question
dig billing.bul.net. NS
Answer
The response has no answer records.
Authority
bul.net. 3600 SOA bsh1.bul.net. noc.bul.net. 2024010775 10800 3600 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0