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DNS on Windows 2000, Second Edition by Cricket Liu, Matt Larson

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Building Up a Large Sitewide Cache with Forwarders

Certain network connections discourage sending large volumes of traffic off-site, either because the network connection is pay-per-packet or because it is a slow link with a high delay, as with a remote office’s satellite connection to the company’s network. In these situations, you want to limit the off-site DNS traffic to the bare minimum. The Microsoft DNS Server has a feature called forwarding to handle this.

If you designate one or more servers at your site as forwarders, all off-site queries are sent to the forwarders first. The idea is that the forwarders handle all off-site queries generated at the site, building up a rich cache of information. For any given query in a remote domain, there is a high probability that the forwarder can answer the query from its cache, avoiding the need for the other servers to send packets off-site. Nothing special is done to these servers to make them forwarders; you modify all the other servers at your site to direct their queries through the forwarders.

A primary master or slave name server’s mode of operation changes slightly when it is directed to use a forwarder. If the requested information is already in its database of authoritative data and cache data, it answers with this information; this part of the operation hasn’t changed. However, if the information is not in its database, the name server sends the query to a forwarder and waits a short period for an answer before resuming ...

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