A forwarder is a network DNS server that forwards DNS queries for external DNS names to DNS servers
outside that network. You also can use conditional forwarders to forward queries according to specific domain names.
A network DNS server is designated a forwarder when other DNS servers in the network forward to it the
queries that they cannot resolve locally. By using a forwarder, you can manage name resolution for names outside your network, such as names on the Internet, and improve the efficiency of name resolution for your network’s computers.
The server that is forwarding requests in the network must be able to communicate with the DNS server that is located on the Internet. This means either you configure it to forward requests to another DNS server or it uses root hints to communicate