sip.cooolbox.bg has no NS records.
NS records for this zone are defined at cooolbox.bg.
NS records for this zone are defined at cooolbox.bg.
Question and response
Question
dig sip.cooolbox.bg. NS
Answer
The response has no answer records.
Authority
cooolbox.bg. 1800 SOA bradley.ns.cloudflare.com. dns.cloudflare.com. 2397213675 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0