# 4. Name Server Operations

## 4.1. Tools for Use With the Name Server Daemon

This section describes several indispensable diagnostic, administrative, and monitoring tools available to the system administrator for controlling and debugging the name server daemon.

### 4.1.1. Diagnostic Tools

The `dig`, `host`, and `nslookup` programs are all command-line tools for manually querying name servers. They differ in style and output format.

`dig`

  `dig` is the most versatile and complete of these lookup tools. It has two modes: simple interactive mode for a single query, and batch mode, which executes a query for each in a list of several query lines. All query options are accessible from the command line.

  For more information and a list of available commands and options, see dig - DNS lookup utility.

`host`

  The `host` utility emphasizes simplicity and ease of use. By default, it converts between host names and Internet addresses, but its functionality can be extended with the use of options.

  For more information and a list of available commands and options, see host - DNS lookup utility.

`nslookup`

  `nslookup` has two modes: interactive and non-interactive. Interactive mode allows the user to query name servers for information about various hosts and domains, or to print a list of hosts in a domain. Non-interactive mode is used to print just the name and requested information for a host or domain.

  Due to its arcane user interface and frequently inconsistent behavior, we do not recommend the use of `nslookup`. Use `dig` instead.

### 4.1.2. Administrative Tools

Administrative tools play an integral part in the management of a server.

`named-checkconf`

  The `named-checkconf` program checks the syntax of a `named.conf` file.

  For more information and a list of available commands and options, see named-checkconf - named configuration file syntax checking tool.

`named-checkzone`

  The `named-checkzone` program checks a zone file for syntax and consistency.

  For more information and a list of available commands and options, see named-checkzone - zone file validation tool.

`named-compilezone`

  This tool is similar to `named-checkzone` but it always dumps the zone content to a specified file (typically in a different format).

  For more information and a list of available commands and options, see named-compilezone - zone file converting tool.

`rndc`

  The remote name daemon control (`rndc`) program allows the system administrator to control the operation of a name server.

  See rndc - name server control utility for details of the available `rndc` commands.

  `rndc` requires a configuration file, since all communication with the server is authenticated with digital signatures that rely on a shared secret, and there is no way to provide that secret other than with a configuration file. The default location for the `rndc` configuration file is `/etc/bind/rndc.conf`, but an alternate location can be specified with the `-c` option. If the configuration file is not found, `rndc` also looks in `/etc/bind/rndc.key` (or whatever `sysconfdir` was defined when the BIND build was configured). The `rndc.key` file is generated by running `rndc-confgen -a` as described in `controls`.

  The format of the configuration file is similar to that of `named.conf`, but is limited to only three blocks: the `options`, `key`, `server`, and the include Directive. These blocks are what associate the secret keys to the servers with which they are meant to be shared. The order of blocks is not significant.

options

  Grammar:

      options {
      	default-key <string>;
      	default-port <integer>;
      	default-server <string>;
      	default-source-address ( <ipv4_address> | * );
      	default-source-address-v6 ( <ipv6_address> | * );
      };

  Blocks: topmost

  default-server

    Grammar: `default-server <string>;`

    Blocks: options

    `default-server` takes a host name or address argument and represents the server that is contacted if no `-s` option is provided on the command line.

  default-key

    Grammar: `default-key <string>;`

    Blocks: options

    `default-key` takes the name of a key as its argument, as defined by a `key` block.

  default-port

    Grammar: `default-port <integer>;`

    Blocks: options

    `default-port` specifies the port to which `rndc` should connect if no port is given on the command line or in a `server` block.

  default-source-address

    Grammar: `default-source-address ( <ipv4_address> | * );`

    Blocks: options

  default-source-address-v6

    Grammar: `default-source-address-v6 ( <ipv6_address> | * );`

    Blocks: options

    `default-source-address` and `default-source-address-v6` specify the IPv4 and IPv6 source address used to communicate with the server if no address is given on the command line or in a `server` block.

key

  Grammar server: `key <string>;`

  Grammar topmost:

      key <string> {
      	algorithm <string>;
      	secret <string>;
      }; // may occur multiple times

  Blocks: topmost, server

  The `key` block defines a key to be used by `rndc` when authenticating with `named`. Its syntax is identical to the `key` statement in `named.conf`. The keyword `key` is followed by a key name, which must be a valid domain name, though it need not actually be hierarchical; thus, a string like `rndc_key` is a valid name. The `key` block has two statements: `algorithm` and `secret`.

  algorithm

    Grammar: `algorithm <string>;`

    Blocks: key

    While the configuration parser accepts any string as the argument to `algorithm`, currently only the strings `hmac-md5`, `hmac-sha1`, `hmac-sha224`, `hmac-sha256`, `hmac-sha384`, and `hmac-sha512` have any meaning.

  secret

    Grammar: `secret <string>;`

    Blocks: key

    The secret is a Base64-encoded string as specified in RFC 3548.

server

  Grammar:

      server <string> {
      	addresses { ( <quoted_string> [ port <integer> ] | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ); ... };
      	key <string>;
      	port <integer>;
      	source-address ( <ipv4_address> | * );
      	source-address-v6 ( <ipv6_address> | * );
      }; // may occur multiple times

  Blocks: topmost

  The `server` block specifies connection parameters for a given server. The server can be specified as a host name or address.

  addresses

    Grammar: `addresses { ( <quoted_string> [ port <integer> ] | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ); ... };`

    Blocks: server

    Specifies one or more addresses to use when communicating with this server.

  `key`

    Associates a key defined using the `key` statement with a server.

  port

    Grammar: `port <integer>;`

    Blocks: server

    Specifes the port `rndc` should connect to on the server.

  source-address

    Grammar: `source-address ( <ipv4_address> | * );`

    Blocks: server

  source-address-v6

    Grammar: `source-address-v6 ( <ipv6_address> | * );`

    Blocks: server

    Overrides `default-source-address` and `default-source-address-v6` for this specific server.

  A sample minimal configuration file is as follows:

      key rndc_key {
           algorithm "hmac-sha256";
           secret
             "c3Ryb25nIGVub3VnaCBmb3IgYSBtYW4gYnV0IG1hZGUgZm9yIGEgd29tYW4K";
      };
      options {
           default-server 127.0.0.1;
           default-key    rndc_key;
      };

  This file, if installed as `/etc/bind/rndc.conf`, allows the command:

  `rndc reload`

  to connect to 127.0.0.1 port 953 and causes the name server to reload, if a name server on the local machine is running with the following controls statements:

      controls {
          inet 127.0.0.1
              allow { localhost; } keys { rndc_key; };
      };

  and it has an identical key block for `rndc_key`.

  Running the `rndc-confgen` program conveniently creates an `rndc.conf` file, and also displays the corresponding `controls` statement needed to add to `named.conf`. Alternatively, it is possible to run `rndc-confgen -a` to set up an `rndc.key` file and not modify `named.conf` at all.

## 4.2. Signals

Certain Unix signals cause the name server to take specific actions, as described in the following table. These signals can be sent using the `kill` command.

`SIGHUP` | Causes the server to read `named.conf` and reload the database.
`SIGTERM` | Causes the server to clean up and exit.
`SIGINT` | Causes the server to clean up and exit.

## 4.3. Plugins

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.

## 4.4. Configuring Plugins

plugin

  Grammar: `plugin ( query ) <string> [ { <unspecified-text> } ]; // may occur multiple times`

  Blocks: topmost, view

  Tags: server

  Configures plugins in `named.conf`.

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 differs depending on the module.

## 4.5. Developing Plugins

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" - a function within the plugin library - is called. 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`.