Plugins are a mechanism to extend the functionality of named using dynamically loadable libraries. By using plugins, core server functionality can be kept simple for the majority of users; more complex code implementing optional features need only be installed by users that need those features. The plugin interface is a work in progress, and is expected to evolve as more plugins are added. Currently, only "query plugins" are supported; these modify the name server query logic. Other plugin types may be added in the future. The only plugin currently included in BIND is filter-aaaa.so, which replaces the filter-aaaa feature that previously existed natively as part of named. The code for this feature has been removed from named, and can no longer be configured using standard named.conf syntax, but linking in the filter-aaaa.so plugin provides identical functionality.

A plugin is configured with the plugin statement in named.conf: plugin query "library.so" { parameters }; In this example, file library.so is the plugin library. query indicates that this is a query plugin. Multiple plugin statements can be specified, to load different plugins or multiple instances of the same plugin. parameters are passed as an opaque string to the plugin's initialization routine. Configuration syntax will differ depending on the module.

Each plugin implements four functions: plugin_register to allocate memory, configure a plugin instance, and attach to hook points within named, plugin_destroy to tear down the plugin instance and free memory, plugin_version to check that the plugin is compatible with the current version of the plugin API, plugin_check to test syntactic correctness of the plugin parameters. At various locations within the named source code, there are "hook points" at which a plugin may register itself. When a hook point is reached while named is running, it is checked to see whether any plugins have registered themselves there; if so, the associated "hook action" is called - this is a function within the plugin library. Hook actions may examine the runtime state and make changes - for example, modifying the answers to be sent back to a client or forcing a query to be aborted. More details can be found in the file lib/ns/include/ns/hooks.h.