DNS on Windows Server 2003, 3rd Edition

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 other cases, a firewall might allow only certain name servers to send queries off the local network to the Internet. In these situations, you don’t necessarily want your name server to follow the standard DNS resolution algorithm and start by sending a query to a root name server. A solution is called forwarding, which changes the way a name server resolves queries it can’t answer itself.

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 for 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. It’s worth pointing out that the terminology is a little funny: a name server configured to forward (or, if you prefer, with forwarding enabled) doesn’t have an official name, but we use the term ...