BIND 9 DNS Library Support

Table of Contents

BIND 9 DNS Library Support
Known Defects/Restrictions
The dns.conf File
Sample Applications
Library References

BIND 9 DNS Library Support

This version of BIND 9 "exports" its internal libraries so that they can be used by third-party applications more easily (we call them "export" libraries in this document). Certain library functions are altered from specific BIND-only behavior to more generic behavior when used by other applications; to enable this generic behavior, the calling program initializes the libraries by calling isc_lib_register().

In addition to DNS-related APIs that are used within BIND 9, the libraries provide the following features:

  • The "DNS client" module. This is a higher level API that provides an interface to name resolution, single DNS transaction with a particular server, and dynamic update. Regarding name resolution, it supports advanced features such as DNSSEC validation and caching. This module supports both synchronous and asynchronous mode.

  • The "IRS" (Information Retrieval System) library. It provides an interface to parse the traditional resolv.conf file and more advanced, DNS-specific configuration file for the rest of this package (see the description for the dns.conf file below).

  • As part of the IRS library, the standard address-name mapping functions, getaddrinfo() and getnameinfo(), are provided. They use the DNSSEC-aware validating resolver backend, and could use other advanced features of the BIND 9 libraries such as caching. The getaddrinfo() function resolves both A and AAAA RRs concurrently when the address family is unspecified.

  • An experimental framework to support other event libraries than BIND 9's internal event task system.


$ make install

Normal installation of BIND will also install library object and header files. Root privilege is normally required.

To see how to build your own application after the installation, see lib/samples/

Known Defects/Restrictions

  • The "fixed" RRset order is not (currently) supported in the export library. If you want to use "fixed" RRset order for, e.g. named while still building the export library even without the fixed order support, build them separately:

    $ ./configure --enable-fixed-rrset [other flags, but not --enable-exportlib]
    $ make
    $ ./configure --enable-exportlib [other flags, but not --enable-fixed-rrset]
    $ cd lib/export
    $ make

  • RFC 5011 is not supported in the validating stub resolver of the export library. In fact, it is not clear whether it should: trust anchors would be a system-wide configuration which would be managed by an administrator, while the stub resolver will be used by ordinary applications run by a normal user.

  • Not all common /etc/resolv.conf options are supported in the IRS library. The only available options in this version are debug and ndots.

The dns.conf File

The IRS library supports an "advanced" configuration file related to the DNS library for configuration parameters that would be beyond the capability of the resolv.conf file. Specifically, it is intended to provide DNSSEC related configuration parameters. By default the path to this configuration file is /etc/dns.conf. This module is very experimental and the configuration syntax or library interfaces may change in future versions. Currently, only the trusted-keys statement is supported, whose syntax is the same as the same statement in named.conf. (See the section called “trusted-keys Statement Grammar” for details.)

Sample Applications

Some sample application programs using this API are provided for reference. The following is a brief description of these applications.

sample: a simple stub resolver utility

Sends a query of a given name (of a given optional RR type) to a specified recursive server and prints the result as a list of RRs. It can also act as a validating stub resolver if a trust anchor is given via a set of command line options.

Usage: sample [options] server_address hostname

Options and Arguments:

-t RRtype

specify the RR type of the query. The default is the A RR.

[-a algorithm] [-e] -k keyname -K keystring

specify a command-line DNS key to validate the answer. For example, to specify the following DNSKEY of

     3600 IN DNSKEY 257 3 5 xxx

specify the options as follows:

-e -k -K "xxx"

-e means that this key is a zone's "key signing key" (also known as "secure entry point"). When -a is omitted rsasha1 will be used by default.

-s domain:alt_server_address

specify a separate recursive server address for the specific "domain". Example: -s


an IP(v4/v6) address of the recursive server to which queries are sent.


the domain name for the query

sample-async: a simple stub resolver, working asynchronously

Similar to "sample", but accepts a list of (query) domain names as a separate file and resolves the names asynchronously.

Usage: sample-async [-s server_address] [-t RR_type] input_file

Options and Arguments:

-s server_address
an IPv4 address of the recursive server to which queries are sent. (IPv6 addresses are not supported in this implementation)
-t RR_type
specify the RR type of the queries. The default is the A RR.
a list of domain names to be resolved. each line consists of a single domain name. Example:

sample-request: a simple DNS transaction client

Sends a query to a specified server, and prints the response with minimal processing. It doesn't act as a "stub resolver": it stops the processing once it gets any response from the server, whether it's a referral or an alias (CNAME or DNAME) that would require further queries to get the ultimate answer. In other words, this utility acts as a very simplified dig.

Usage: sample-request [-t RRtype] server_address hostname

Options and Arguments:

-t RRtype

specify the RR type of the queries. The default is the A RR.


an IP(v4/v6) address of the recursive server to which the query is sent.


the domain name for the query

sample-gai: getaddrinfo() and getnameinfo() test code

This is a test program to check getaddrinfo() and getnameinfo() behavior. It takes a host name as an argument, calls getaddrinfo() with the given host name, and calls getnameinfo() with the resulting IP addresses returned by getaddrinfo(). If the dns.conf file exists and defines a trust anchor, the underlying resolver will act as a validating resolver, and getaddrinfo()/getnameinfo() will fail with an EAI_INSECUREDATA error when DNSSEC validation fails.

Usage: sample-gai hostname

sample-update: a simple dynamic update client program

Accepts a single update command as a command-line argument, sends an update request message to the authoritative server, and shows the response from the server. In other words, this is a simplified nsupdate.

Usage: sample-update [options] (add|delete) "update data"

Options and Arguments:

-a auth_server

An IP address of the authoritative server that has authority for the zone containing the update name. This should normally be the primary authoritative server that accepts dynamic updates. It can also be a secondary server that is configured to forward update requests to the primary server.

-k keyfile

A TSIG key file to secure the update transaction. The keyfile format is the same as that for the nsupdate utility.

-p prerequisite

A prerequisite for the update (only one prerequisite can be specified). The prerequisite format is the same as that is accepted by the nsupdate utility.

-r recursive_server

An IP address of a recursive server that this utility will use. A recursive server may be necessary to identify the authoritative server address to which the update request is sent.

-z zonename

The domain name of the zone that contains


Specify the type of update operation. Either "add" or "delete" must be specified.

"update data"

Specify the data to be updated. A typical example of the data would look like "name TTL RRtype RDATA".


In practice, either -a or -r must be specified. Others can be optional; the underlying library routine tries to identify the appropriate server and the zone name for the update.

Examples: assuming the primary authoritative server of the zone has an IPv6 address 2001:db8::1234,

$ sample-update -a sample-update -k Kxxx.+nnn+mmmm.key add " 30 IN A"

adds an A RR for using the given key.

$ sample-update -a sample-update -k Kxxx.+nnn+mmmm.key delete " 30 IN A"

removes all A RRs for using the given key.

$ sample-update -a sample-update -k Kxxx.+nnn+mmmm.key delete ""

removes all RRs for using the given key.

nsprobe: domain/name server checker in terms of RFC 4074

Checks a set of domains to see the name servers of the domains behave correctly in terms of RFC 4074. This is included in the set of sample programs to show how the export library can be used in a DNS-related application.

Usage: nsprobe [-d] [-v [-v...]] [-c cache_address] [input_file]



Run in "debug" mode. With this option nsprobe will dump every RRs it receives.


Increase verbosity of other normal log messages. This can be specified multiple times.

-c cache_address

Specify an IP address of a recursive (caching) name server. nsprobe uses this server to get the NS RRset of each domain and the A and/or AAAA RRsets for the name servers. The default value is


A file name containing a list of domain (zone) names to be probed. when omitted the standard input will be used. Each line of the input file specifies a single domain name such as "". In general this domain name must be the apex name of some DNS zone (unlike normal "host names" such as ""). nsprobe first identifies the NS RRsets for the given domain name, and sends A and AAAA queries to these servers for some "widely used" names under the zone; specifically, adding "www" and "ftp" to the zone name.

Library References

As of this writing, there is no formal "manual" for the libraries, except this document, header files (some of which provide pretty detailed explanations), and sample application programs.

BIND 9.12.4-P2