2k forwader and 2k3,2k8 conditional forwaders
A windows server is not authorative for a zone, and that a DNS server can’t resolve locally it can forward DNS resolution requests to another DNS servers .
When a client queried in DNS, the way it responds depends on the type of query issued, which can be either iterative or recursive. In an iterative query, the client asks the name server for the best possible answer to its query. The name server checks its cache and the zones for which it is authoritative and returns the best possible answer to the client.
In a recursive query,client demands either a full answer (the IP address of the target host) .
Conditional Forwarding feature that is included in Windows Server 2003 and 2008.
Conditional DNS forwarding is a useful feature that avoids the usual recursive nature of DNS resolution requests, in which DNS must first find DNS servers for .com, then microsoft.com, and so on. If you have a large namespace,consider using conditional DNS forwarding to speed up resolution requests. This feature is also useful for connecting Organization uses a nonstandard namespace.(ie microsoft.local)
In windows 2000 forwader
In windows2003 conditional forwader