Learning Windows Server 2003

Forwarding

Forwarding, in the simplest terms, is the process by which a nameserver passes on requests it cannot answer locally to another server. You can make forwarding work to your advantage so that you effectively combine the resolver caches for many nameservers into one. By doing this, you allow clients to resolve previously retrieved sites from that “mega-cache” before requiring a true refresh lookup of the information from authoritative nameservers on the public Internet.

Here’s how it works. DNS behavior by default is to consult the preferred nameserver first to see if it has the necessary zone information for which the client is searching. It doesn’t matter to the client if the preferred nameserver has the zone information but isn’t authoritative; having the information is enough for the client, and it takes the returned results and performs the connection process. But if the server doesn’t have the zone recorded in its files, it must go upstream, to the public Internet, to ask other nameservers for the zone information that’s needed. This takes time because it adds a delay to the initial resolution while the preferred nameserver is searching the Internet for the answer. However, after the server looks up the information once, it stores it in its cache of resolved names so that the next user looking for the same resolver information doesn’t incur that delay: the preferred nameserver simply can answer out of its cache and return the data nearly instantaneously.

Forwarding ...