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Dynamic DNS

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The Client

The DNS update client can either be a DHCP server or a machine that gets a dynamic address assigned to it by some mechanism, such as PPP or DHCP. Which model to use is an administrative policy decision, to which I will return later.

The nsupdate command-line tool is for making updates to dynamic zones. It can be used by hand or scripted. As a standard UNIX tool, it will read commands from stdin, print messages to stdout, and send errors to stderr.

With this tool you can edit zones, unconditionally or conditionally. The point of conditional edits is to enforce administrative policies. If a DHCP server knows that it should never enter new names into the zone, it might supply the condition that the name already exists before doing any updates. On the other hand, if the DHCP server knows that it should never overwrite a name that is already present in the zone, it might submit that as a condition for the update. All updates are atomic: The conditions and updates are submitted as one request, which is either acted upon or rejected because of failed prerequisites.


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