The act of forwarding refers to the relaying of a DNS request from one server toanother one, when the first server is unable to process the request. This is especiallyuseful in resolving Internet names to their associated IP addresses. Byusing a forwarder, the internal DNS server passes off the act of locating anexternal resource, thereby reducing its processing load and network bandwidth.
The use of forwarding is also helpful for protecting internal DNS servers fromaccess by unauthorized Internet users. It works in the following manner:
A client issues a request for a FQDN on a zone for which its preferredDNS server is not authoritative (for example, an Internet domain such aswww.systemadministrator.in).
The local DNS server receives this request but has zone informationonly for the internal local domain and checks its list of forwarders.
Finding the IP address of an external DNS server (such as one hosted bythe company’s ISP), the local DNS server forwards the request to theexternal server (forwarder).
The forwarder attempts to resolve the required FQDN and returns theresult to the internal DNS server, which then returns the result to therequesting client.
You can configure a DNS server as a conditional forwarder. This is a DNS serverthat handles name resolution for specified domains only. In other words, thelocal DNS server will forward all the queries that it receives for names endingwith a specific domain name to the conditional forwarder.