Let's say we have name server A who serves for the domain name
example.com and its subdomains.
Then we have another name server B who would want to avail the
custom-subdomain.example.com from name server A.
The purpose of the name server B is to serve A-records for the domain name
custom-subdomain.example.com and its subdomains ex:
In other words, server A is the parent zone while server B is the child zone.
With the following setup, who needs to serve the SOA-record for the child zone? The parent zone (A) or the child zone (B) itself?