Q. What's conditional DNS forwarding?

A. Windows 2000 Server DNS can forward DNS resolution requests that a DNS server can't resolve locally. This forwarding occurs when the request is for a domain for which the DNS server isn't authoritative and the request isn't in the DNS server's cache waiting to be forwarded to another DNS server. The ability to forward DNS resolution requests is a global setting that applies to all unresolvable addresses.

Windows Server 2003 offers the ability to forward unresolvable requests to different DNS servers. Depending on the domain in which the request originated and whether the request matches multiple defined forwarding rules, the DNS server uses the IP address that corresponds to the forwarding rule that most closely matches the resolution request. For example, if a DNS server has forwarding configured as the table shows, the DNS server will forward a request for host143.marketing.ntfaq.com to 192.168.40.40, because that IP address is a closer match to marketing.ntfaq.com than it is to ntfaq.com.

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 ntfaq.com, and so on. If you have a large namespace, you might consider using conditional DNS forwarding to speed up resolution requests. This feature is also useful for connecting two organizations, especially if one organization uses a nonstandard namespace--for example, savilltech.local--that the typical DNS name-resolution process would never find.