а. Configure delegation
DNS delegation is when a DNS server delegates authority over a part of its namespace to one or more other DNS servers. For example,
Adatum.com and
sales.adatum.com could be hosted in the same zone,
Adatum.com, with the
sales.adatum.com merely being a subdomain record. In this case, the authoritative DNS servers for
Adatum.com and
sales.adatum.com are the same. There is no need for the DNS servers in
Adatum.com to refer recursive DNS servers to another domain. - это чтоли?