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# BIND 9

### Contents

1. [Introduction](#intro)
1. [Reporting bugs and getting help](#help)
1. [Contributing to BIND](#contrib)
1. [BIND 9.11 features](#features)
1. [Building BIND](#build)
1. [macOS](#macos)
1. [Dependencies](#dependencies)
1. [Compile-time options](#opts)
1. [Automated testing](#testing)
1. [Documentation](#doc)
1. [Change log](#changes)
1. [Acknowledgments](#ack)

### <a name="intro"/> Introduction

BIND (Berkeley Internet Name Domain) is a complete, highly portable
implementation of the DNS (Domain Name System) protocol.

The BIND name server, `named`, is able to serve as an authoritative name
server, recursive resolver, DNS forwarder, or all three simultaneously.  It
implements views for split-horizon DNS, automatic DNSSEC zone signing and
key management, catalog zones to facilitate provisioning of zone data
throughout a name server constellation, response policy zones (RPZ) to
protect clients from malicious data, response rate limiting (RRL) and
recursive query limits to reduce distributed denial of service attacks,
and many other advanced DNS features.  BIND also includes a suite of
administrative tools, including the `dig` and `delv` DNS lookup tools,
`nsupdate` for dynamic DNS zone updates, `rndc` for remote name server
administration, and more.

BIND 9 is a complete re-write of the BIND architecture that was used in
versions 4 and 8.  Internet Systems Consortium
([https://www.isc.org](https://www.isc.org)), a 501(c)(3) public benefit
corporation dedicated to providing software and services in support of the
Internet infrastructure, developed BIND 9 and is responsible for its
ongoing maintenance and improvement.  BIND is open source software
licensed under the terms of ISC License for all versions up to and
including BIND 9.10, and the Mozilla Public License version 2.0 for all
subsequent versions.

For a summary of features introduced in past major releases of BIND,
see the file [HISTORY](HISTORY.md).

For a detailed list of changes made throughout the history of BIND 9, see
the file [CHANGES](CHANGES). See [below](#changes) for details on the
CHANGES file format.

For up-to-date versions and release notes, see
[https://www.isc.org/download/](https://www.isc.org/download/).

### <a name="help"/> Reporting bugs and getting help

To report non-security-sensitive bugs or request new features, you may
open an Issue in the BIND 9 project on the
[ISC GitLab server](https://gitlab.isc.org) at
[https://gitlab.isc.org/isc-projects/bind9](https://gitlab.isc.org/isc-projects/bind9).

Please note that, unless you explicitly mark the newly created Issue as
"confidential", it will be publicly readable.  Please do not include any
information in bug reports that you consider to be confidential unless
the issue has been marked as such.  In particular, if submitting the
contents of your configuration file in a non-confidential Issue, it is
advisable to obscure key secrets: this can be done automatically by
using `named-checkconf -px`.

If the bug you are reporting is a potential security issue, such as an
assertion failure or other crash in `named`, please do *NOT* use GitLab to
report it. Instead, send mail to
[security-officer@isc.org](mailto:security-officer@isc.org) using our
OpenPGP key to secure your message. (Information about OpenPGP and links
to our key can be found at
[https://www.isc.org/pgpkey](https://www.isc.org/pgpkey).) Please do not
discuss the bug on any public mailing list.

For a general overview of ISC security policies, read the Knowledge Base
article at [https://kb.isc.org/docs/aa-00861](https://kb.isc.org/docs/aa-00861).

Professional support and training for BIND are available from
ISC at [https://www.isc.org/support](https://www.isc.org/support).

To join the __BIND Users__ mailing list, or view the archives, visit
[https://lists.isc.org/mailman/listinfo/bind-users](https://lists.isc.org/mailman/listinfo/bind-users).

If you're planning on making changes to the BIND 9 source code, you
may also want to join the __BIND Workers__ mailing list, at
[https://lists.isc.org/mailman/listinfo/bind-workers](https://lists.isc.org/mailman/listinfo/bind-workers).

### <a name="contrib"/> Contributing to BIND

ISC maintains a public git repository for BIND; details can be found
at [http://www.isc.org/git/](http://www.isc.org/git/).

Information for BIND contributors can be found in the following files:
- General information: [doc/dev/contrib.md](doc/dev/contrib.md)
- BIND 9 code style: [doc/dev/style.md](doc/dev/style.md)
- BIND architecture and developer guide: [doc/dev/dev.md](doc/dev/dev.md)

Patches for BIND may be submitted as
[merge requests](https://gitlab.isc.org/isc-projects/bind9/merge_requests)
in the [ISC GitLab server](https://gitlab.isc.org) at
at [https://gitlab.isc.org/isc-projects/bind9/merge_requests](https://gitlab.isc.org/isc-projects/bind9/merge_requests).

By default, external contributors don't have ability to fork BIND in the
GitLab server, but if you wish to contribute code to BIND, you may request
permission to do so. Thereafter, you can create git branches and directly
submit requests that they be reviewed and merged.

If you prefer, you may also submit code by opening a
[GitLab Issue](https://gitlab.isc.org/isc-projects/bind9/issues) and
including your patch as an attachment, preferably generated by
`git format-patch`.

### <a name="features"/> BIND 9.11 features

BIND 9.11.0 includes a number of changes from BIND 9.10 and earlier
releases.  New features include:

* Added support for Catalog Zones, a new method for provisioning servers: a
  list of zones to be served is stored in a DNS zone, along with their
  configuration parameters. Changes to the catalog zone are propagated to
  slaves via normal AXFR/IXFR, whereupon the zones that are listed in it
  are automatically added, deleted or reconfigured.
* Added support for "dnstap", a fast and flexible method of capturing and
  logging DNS traffic.
* Added support for "dyndb", a new API for loading zone data from an
  external database, developed by Red Hat for the FreeIPA project.
* "fetchlimit" quotas are now compiled in by default.  These are for the
  use of recursive resolvers that are are under high query load for domains
  whose authoritative servers are nonresponsive or are experiencing a
  denial of service attack:
    * `fetches-per-server` limits the number of simultaneous queries that
      can be sent to any single authoritative server.  The configured value
      is a starting point; it is automatically adjusted downward if the
      server is partially or completely non-responsive. The algorithm used
      to adjust the quota can be configured via the "fetch-quota-params"
      option.
    * `fetches-per-zone` limits the number of simultaneous queries that can
      be sent for names within a single domain.  (Note: Unlike
      `fetches-per-server`, this value is not self-tuning.)
    * New stats counters have been added to count queries spilled due to
      these quotas.
* Added a new `dnssec-keymgr` key maintenance utility, which can generate or
  update keys as needed to ensure that a zone's keys match a defined DNSSEC
  policy.
* The experimental "SIT" feature in BIND 9.10 has been renamed "COOKIE" and
  is no longer optional. EDNS COOKIE is a mechanism enabling clients to
  detect off-path spoofed responses, and servers to detect spoofed-source
  queries.  Clients that identify themselves using COOKIE options are not
  subject to response rate limiting (RRL) and can receive larger UDP
  responses.
* SERVFAIL responses can now be cached for a limited time (defaulting to 1
  second, with an upper limit of 30).  This can reduce the frequency of
  retries when a query is persistently failing.
* Added an `nsip-wait-recurse` switch to RPZ. This causes NSIP rules to be
  skipped if a name server IP address isn't in the cache yet; the address
  will be looked up and the rule will be applied on future queries.
* Added a Python RNDC module. This allows multiple commands to sent over a
  persistent RNDC channel, which saves time.
* The `controls` block in named.conf can now grant read-only `rndc` access
  to specified clients or keys. Read-only clients could, for example, check
  `rndc status` but could not reconfigure or shut down the server.
* `rndc` commands can now return arbitrarily large amounts of text to the
  caller.
* The zone serial number of a dynamically updatable zone can now be set via
  `rndc signing -serial <number> <zonename>`.  This allows inline-signing
  zones to be set to a specific serial number.
* The new `rndc nta` command can be used to set a Negative Trust Anchor
  (NTA), disabling DNSSEC validation for a specific domain; this can be
  used when responses from a domain are known to be failing validation due
  to administrative error rather than because of a spoofing attack.
  Negative trust anchors are strictly temporary; by default they expire
  after one hour, but can be configured to last up to one week.
* `rndc delzone` can now be used on zones that were not originally created
  by "rndc addzone".
* `rndc modzone` reconfigures a single zone, without requiring the entire
  server to be reconfigured.
* `rndc showzone` displays the current configuration of a zone.
* `rndc managed-keys` can be used to check the status of RFC 5001 managed
  trust anchors, or to force trust anchors to be refreshed.
* `max-cache-size` can now be set to a percentage of available memory. The
  default is 90%.
* Update forwarding performance has been improved by allowing a single TCP
  connection to be shared by multiple updates.
* The EDNS Client Subnet (ECS) option is now supported for authoritative
  servers; if a query contains an ECS option then ACLs containing `geoip`
  or `ecs` elements can match against the the address encoded in the
  option.  This can be used to select a view for a query, so that different
  answers can be provided depending on the client network.
* The EDNS EXPIRE option has been implemented on the client side, allowing
  a slave server to set the expiration timer correctly when transferring
  zone data from another slave server.
* The key generation and manipulation tools (`dnssec-keygen`,
  `dnssec-settime`, `dnssec-importkey`, `dnssec-keyfromlabel`) now take
  `-Psync` and `-Dsync` options to set the publication and deletion times
  of CDS and CDNSKEY parent-synchronization records.  Both `named` and
  `dnssec-signzone` can now publish and remove these records at the
  scheduled times.
* A new `minimal-any` option reduces the size of UDP responses for query
  type ANY by returning a single arbitrarily selected RRset instead of all
  RRsets.
* A new `masterfile-style` zone option controls the formatting of text zone
  files:  When set to `full`, a zone file is dumped in
  single-line-per-record format.
* `serial-update-method` can now be set to `date`. On update, the serial
  number will be set to the current date in YYYYMMDDNN format.
* `dnssec-signzone -N date` sets the serial number to YYYYMMDDNN.
* `named -L <filename>` causes named to send log messages to the specified
  file by default instead of to the system log.
* `dig +ttlunits` prints TTL values with time-unit suffixes: w, d, h, m, s
  for weeks, days, hours, minutes, and seconds.
* `dig +unknownformat` prints dig output in RFC 3597 "unknown record"
  presentation format.
* `dig +ednsopt` allows dig to set arbitrary EDNS options on requests.
* `dig +ednsflags` allows dig to set yet-to-be-defined EDNS flags on
  requests.
* `mdig` is an alternate version of dig which sends multiple pipelined TCP
  queries to a server.  Instead of waiting for a response after sending a
  query, it sends all queries immediately and displays responses in the
  order received.
* `serial-query-rate` no longer controls NOTIFY messages.  These are
  separately controlled by `notify-rate` and `startup-notify-rate`.
* `nsupdate` now performs `check-names` processing by default on records to
  be added.  This can be disabled with `check-names no`.
* The statistics channel now supports DEFLATE compression, reducing the
  size of the data sent over the network when querying statistics.
* New counters have been added to the statistics channel to track the sizes
  of incoming queries and outgoing responses in histogram buckets, as
  specified in RSSAC002.
* A new NXDOMAIN redirect method (option `nxdomain-redirect`) has been
  added, allowing redirection to a specified DNS namespace instead of a
  single redirect zone.
* When starting up, named now ensures that no other named process is
  already running.
* Files created by named to store information, including `mkeys` and `nzf`
  files, are now named after their corresponding views unless the view name
  contains characters incompatible with use as a filename. Old style
  filenames (based on the hash of the view name) will still work.

#### BIND 9.11.1
	
BIND 9.11.1 is a maintenance release, and addresses the security
flaws disclosed in CVE-2016-6170, CVE-2016-8864, CVE-2016-9131,
CVE-2016-9147, CVE-2016-9444, CVE-2016-9778, CVE-2017-3135,
CVE-2017-3136, CVE-2017-3137 and CVE-2017-3138.

#### BIND 9.11.2

BIND 9.11.2 is a maintenance release, and addresses the security flaws
disclosed in CVE-2017-3140, CVE-2017-3141, CVE-2017-3142 and CVE-2017-3143.
It also addresses several bugs related to the use of an LMDB database to
store data related to zones added via `rndc addzone` or catalog zones.

#### BIND 9.11.3

BIND 9.11.3 is a maintenance release, and addresses the security flaw
disclosed in CVE-2017-3145.

#### BIND 9.11.4

BIND 9.11.4 is a maintenance release, and addresses the security flaw
disclosed in CVE-2018-5738. It also introduces "root key sentinel" support,
enabling validating resolvers to indicate via a special query which trust
anchors are configured for the root zone.

#### BIND 9.11.5

BIND 9.11.5 is a maintenance release, and also addresses CVE-2018-5741
by correcting faulty documentation and introducing the following new
feature:

* New `krb5-selfsub` and `ms-selfsub` rule types for `update-policy`
  statements allow updating of subdomains based on a Kerberos or
  Active Directory machine principal.

#### BIND 9.11.6

BIND 9.11.6 is a maintenance release, and also addresses the security
flaws disclosed in CVE-2018-5743, CVE-2018-5745, CVE-2018-5744,
and CVE-2019-6465.

#### BIND 9.11.7

BIND 9.11.7 is a maintenance release, and also addresses the security
flaw disclosed in CVE-2018-5743.

#### BIND 9.11.8

BIND 9.11.8 is a maintenance release, and also addresses the security
flaw disclosed in CVE-2019-6471.

#### BIND 9.11.9

BIND 9.11.9 is a maintenance release, and also adds support for
the new MaxMind GeoIP2 geolocation API when built with
`configure --with-geoip2`.

#### BIND 9.11.10

BIND 9.11.10 is a maintenance release.

#### BIND 9.11.11

BIND 9.11.11 is a maintenance release.

#### BIND 9.11.12

BIND 9.11.12 is a maintenance release.

#### BIND 9.11.13

BIND 9.11.13 is a maintenance release, and also addresses the security
vulnerability disclosed in CVE-2019-6477.

#### BIND 9.11.14

BIND 9.11.14 is a maintenance release.

#### BIND 9.11.15

BIND 9.11.15 is a maintenance release.

#### BIND 9.11.16

BIND 9.11.16 is a maintenance release.

#### BIND 9.11.17

BIND 9.11.17 is a maintenance release.

#### BIND 9.11.18

BIND 9.11.18 is a maintenance release.

#### BIND 9.11.19

BIND 9.11.19 is a maintenance release, and also addresses the security
vulnerabilities disclosed in CVE-2020-8616 and CVE-2020-8617.

#### BIND 9.11.20

BIND 9.11.20 is a maintenance release, and also addresses the security
vulnerability disclosed in CVE-2020-8619.

#### BIND 9.11.21

BIND 9.11.21 is a maintenance release.

#### BIND 9.11.22

BIND 9.11.22 is a maintenance release, and also addresses the security
vulnerabilities disclosed in CVE-2020-8622, CVE-2020-8623, and
CVE-2020-8624.

#### BIND 9.11.23

BIND 9.11.23 is a maintenance release.

#### BIND 9.11.24

BIND 9.11.24 is a maintenance release.

#### BIND 9.11.25

BIND 9.11.25 is a maintenance release.

#### BIND 9.11.26

BIND 9.11.26 is a maintenance release.

#### BIND 9.11.27

BIND 9.11.27 is a maintenance release.

#### BIND 9.11.28

BIND 9.11.28 is a maintenance release, and also addresses the security
vulnerability disclosed in CVE-2020-8625.

#### BIND 9.11.29

BIND 9.11.29 is a maintenance release.

#### BIND 9.11.30

This release was withdrawn.

#### BIND 9.11.31

BIND 9.11.31 is a maintenance release, and also addresses the security
vulnerabilities disclosed in CVE-2021-25214, CVE-2021-25215, and
CVE-2021-25216.

#### BIND 9.11.32

BIND 9.11.32 is a maintenance release.

#### BIND 9.11.33

BIND 9.11.33 is a maintenance release.

#### BIND 9.11.34

BIND 9.11.34 is a maintenance release.

#### BIND 9.11.35

BIND 9.11.35 is a maintenance release.

#### BIND 9.11.36

BIND 9.11.36 is a maintenance release, and also addresses the security
vulnerability disclosed in CVE-2021-25219.

#### BIND 9.11.37

BIND 9.11.37 is a maintenance release, and also addresses the security
vulnerability disclosed in CVE-2021-25220.

### <a name="build"/> Building BIND

Minimally, BIND requires a UNIX or Linux system with an ANSI C compiler,
basic POSIX support, and a 64-bit integer type. Successful builds have been
observed on many versions of Linux and UNIX, including RHEL/CentOS/Oracle Linux,
Fedora, Debian, Ubuntu, SLES, openSUSE, Slackware, Alpine, FreeBSD, NetBSD,
OpenBSD, macOS, Solaris, OpenIndiana, OmniOS CE, HP-UX, and OpenWRT.

BIND is also available for Windows Server 2008 and higher.  See
`win32utils/build.txt` for details on building for Windows
systems.

To build on a UNIX or Linux system, use:

		$ ./configure
		$ make

If you're planning on making changes to the BIND 9 source, you should run
`make depend`.  If you're using Emacs, you might find `make tags` helpful.

Several environment variables that can be set before running `configure` will
affect compilation.  Significant ones are:

|Variable|Description |
|--------------------|-----------------------------------------------|
|`CC`|The C compiler to use.  `configure` tries to figure out the right one for supported systems.|
|`CFLAGS`|C compiler flags.  Defaults to include -g and/or -O2 as supported by the compiler.  Please include '-g' if you need to set `CFLAGS`. |
|`STD_CINCLUDES`|System header file directories.  Can be used to specify where add-on thread or IPv6 support is, for example.  Defaults to empty string.|
|`STD_CDEFINES`|Any additional preprocessor symbols you want defined.  Defaults to empty string. For a list of possible settings, see the file [OPTIONS](OPTIONS.md).|
|`LDFLAGS`|Linker flags. Defaults to empty string.|
|`BUILD_CC`|Needed when cross-compiling: the native C compiler to use when building for the target system.|
|`BUILD_CFLAGS`|`CFLAGS` for the target system during cross-compiling.|
|`BUILD_CPPFLAGS`|`CPPFLAGS` for the target system during cross-compiling.|
|`BUILD_LDFLAGS`|`LDFLAGS` for the target system during cross-compiling.|
|`BUILD_LIBS`|`LIBS` for the target system during cross-compiling.|

Additional environment variables affecting the build are listed at the
end of the `configure` help text, which can be obtained by running the
command:

    $ ./configure --help

On platforms where neither the C11 Atomic operations library nor custom ISC
atomic operations are available, updating the statistics counters is not
locked due to performance reasons and therefore the counters might be
inaccurate.  Anybody building BIND 9 is strongly advised to use a modern
C11 compiler with C11 Atomic operations library support.

#### <a name="macos"> macOS

Building on macOS assumes that the "Command Tools for Xcode" is installed.
This can be downloaded from
[https://developer.apple.com/download/more/](https://developer.apple.com/download/more/)
or, if you have Xcode already installed, you can run `xcode-select
--install`.  (Note that an Apple ID may be required to access the download
page.)

### <a name="dependencies"/> Dependencies

Portions of BIND that are written in Python, including
`dnssec-keymgr`, `dnssec-coverage`, `dnssec-checkds`, and some of the
system tests, require the `argparse`, `ply` and `distutils.core` modules
to be available.
`argparse` is a standard module as of Python 2.7 and Python 3.2.
`ply` is available from [https://pypi.python.org/pypi/ply](https://pypi.python.org/pypi/ply).
`distutils.core` is required for installation.

#### <a name="opts"/> Compile-time options

To see a full list of configuration options, run `configure --help`.

On most platforms, BIND 9 is built with multithreading support, allowing it
to take advantage of multiple CPUs.  You can configure this by specifying
`--enable-threads` or `--disable-threads` on the `configure` command line.
The default is to enable threads, except on some older operating systems on
which threads are known to have had problems in the past.  (Note: Prior to
BIND 9.10, the default was to disable threads on Linux systems; this has
now been reversed.  On Linux systems, the threaded build is known to change
BIND's behavior with respect to file permissions; it may be necessary to
specify a user with the -u option when running `named`.)

To build shared libraries, specify `--with-libtool` on the `configure`
command line.

For the server to support DNSSEC, you need to build it with crypto support.
To use OpenSSL, you should have OpenSSL 1.0.2e or newer installed.  If the
OpenSSL library is installed in a nonstandard location, specify the prefix
using `--with-openssl=<PREFIX>` on the configure command line. To use a
PKCS#11 hardware service module for cryptographic operations, specify the
path to the PKCS#11 provider library using `--with-pkcs11=<PREFIX>`, and
configure BIND with "--enable-native-pkcs11".

To support the HTTP statistics channel, the server must be linked with at
least one of the following libraries: `libxml2`
[http://xmlsoft.org](http://xmlsoft.org) or `json-c`
[https://github.com/json-c/json-c](https://github.com/json-c/json-c).
If these are installed at a nonstandard location, then:

* for `libxml2`, specify the prefix using `--with-libxml2=/prefix`,
* for `json-c`, adjust `PKG_CONFIG_PATH`.

To support compression on the HTTP statistics channel, the server must be
linked against `libzlib`.  If this is installed in a nonstandard location,
specify the prefix using `--with-zlib=/prefix`.

To support storing configuration data for runtime-added zones in an LMDB
database, the server must be linked with liblmdb. If this is installed in a
nonstandard location, specify the prefix using `with-lmdb=/prefix`.

To support GeoIP location-based ACLs, the server must be linked with
libGeoIP. This is not turned on by default; BIND must be configured with
"--with-geoip". If the library is installed in a nonstandard location, use
specify the prefix using "--with-geoip=/prefix".

For DNSTAP packet logging, you must have installed `libfstrm`
[https://github.com/farsightsec/fstrm](https://github.com/farsightsec/fstrm)
and `libprotobuf-c`
[https://developers.google.com/protocol-buffers](https://developers.google.com/protocol-buffers),
and BIND must be configured with `--enable-dnstap`.

Certain compiled-in constants and default settings can be increased to
values better suited to large servers with abundant memory resources (e.g,
64-bit servers with 12G or more of memory) by specifying
`--with-tuning=large` on the `configure` command line. This can improve
performance on big servers, but will consume more memory and may degrade
performance on smaller systems.

On some platforms it is necessary to explicitly request large file support
to handle files bigger than 2GB.  This can be done by using
`--enable-largefile` on the `configure` command line.

Support for the "fixed" rrset-order option can be enabled or disabled by
specifying `--enable-fixed-rrset` or `--disable-fixed-rrset` on the
configure command line.  By default, fixed rrset-order is disabled to
reduce memory footprint.

If your operating system has integrated support for IPv6, it will be used
automatically.  If you have installed KAME IPv6 separately, use
`--with-kame[=PATH]` to specify its location.

The `--enable-querytrace` option causes `named` to log every step of
processing every query. This should only be enabled when debugging, because
it has a significant negative impact on query performance.

`make install` will install `named` and the various BIND 9 libraries.  By
default, installation is into /usr/local, but this can be changed with the
`--prefix` option when running `configure`.

You may specify the option `--sysconfdir` to set the directory where
configuration files like `named.conf` go by default, and `--localstatedir`
to set the default parent directory of `run/named.pid`.   For backwards
compatibility with BIND 8, `--sysconfdir` defaults to `/etc` and
`--localstatedir` defaults to `/var` if no `--prefix` option is given.  If
there is a `--prefix` option, sysconfdir defaults to `$prefix/etc` and
localstatedir defaults to `$prefix/var`.

### <a name="testing"/> Automated testing

A system test suite can be run with `make test`.  The system tests require
you to configure a set of virtual IP addresses on your system (this allows
multiple servers to run locally and communicate with one another).  These
IP addresses can be configured by running the command
`bin/tests/system/ifconfig.sh up` as root.

Some tests require Perl and the `Net::DNS` and/or `IO::Socket::INET6` modules,
and will be skipped if these are not available. Some tests require Python
and the `dnspython` module and will be skipped if these are not available.
See bin/tests/system/README for further details.

Unit tests are implemented using the [CMocka unit testing framework](https://cmocka.org/).
To build them, use `configure --with-cmocka`. Execution of tests is done
by the [Kyua test execution engine](https://github.com/jmmv/kyua); if the
`kyua` command is available, then unit tests can be run via `make test`
or `make unit`.

### <a name="doc"/> Documentation

The *BIND 9 Administrator Reference Manual* is included with the source
distribution, in DocBook XML, HTML, and PDF format, in the `doc/arm`
directory.

Some of the programs in the BIND 9 distribution have man pages in their
directories.  In particular, the command line options of `named` are
documented in `bin/named/named.8`.

Frequently (and not-so-frequently) asked questions and their answers
can be found in the ISC Knowledge Base at
[https://kb.isc.org](https://kb.isc.org).

Additional information on various subjects can be found in other
`README` files throughout the source tree.

### <a name="changes"/> Change log

A detailed list of all changes that have been made throughout the
development BIND 9 is included in the file CHANGES, with the most recent
changes listed first.  Change notes include tags indicating the category of
the change that was made; these categories are:

|Category	|Description	        			|
|--------------	|-----------------------------------------------|
| [func] | New feature |
| [bug] | General bug fix |
| [security] | Fix for a significant security flaw |
| [experimental] | Used for new features when the syntax or other aspects of the design are still in flux and may change |
| [port] | Portability enhancement |
| [maint] | Updates to built-in data such as root server addresses and keys |
| [tuning] | Changes to built-in configuration defaults and constants to improve performance |
| [performance] | Other changes to improve server performance |
| [protocol] | Updates to the DNS protocol such as new RR types |
| [test] | Changes to the automatic tests, not affecting server functionality |
| [cleanup] | Minor corrections and refactoring |
| [doc] | Documentation |
| [contrib] | Changes to the contributed tools and libraries in the 'contrib' subdirectory |
| [placeholder] | Used in the master development branch to reserve change numbers for use in other branches, e.g. when fixing a bug that only exists in older releases |

In general, [func] and [experimental] tags will only appear in new-feature
releases (i.e., those with version numbers ending in zero).  Some new
functionality may be backported to older releases on a case-by-case basis.
All other change types may be applied to all currently-supported releases.

#### Bug report identifiers

Most notes in the CHANGES file include a reference to a bug report or
issue number. Prior to 2018, these were usually of the form `[RT #NNN]`
and referred to entries in the "bind9-bugs" RT database, which was not open
to the public. More recent entries use the form `[GL #NNN]` or, less often,
`[GL !NNN]`, which, respectively, refer to issues or merge requests in the
GitLab database. Most of these are publicly readable, unless they include
information which is confidential or security sensitive.

To look up a GitLab issue by its number, use the URL
[https://gitlab.isc.org/isc-projects/bind9/issues/NNN](https://gitlab.isc.org/isc-projects/bind9/issues).
To look up a merge request, use
[https://gitlab.isc.org/isc-projects/bind9/merge_requests/NNN](https://gitlab.isc.org/isc-projects/bind9/merge_requests).

In rare cases, an issue or merge request number may be followed with the
letter "P". This indicates that the information is in the private ISC
GitLab instance, which is not visible to the public.

### <a name="ack"/> Acknowledgments

* The original development of BIND 9 was underwritten by the
  following organizations:

		Sun Microsystems, Inc.
		Hewlett Packard
		Compaq Computer Corporation
		IBM
		Process Software Corporation
		Silicon Graphics, Inc.
		Network Associates, Inc.
		U.S. Defense Information Systems Agency
		USENIX Association
		Stichting NLnet - NLnet Foundation
		Nominum, Inc.

* This product includes software developed by the OpenSSL Project for use
  in the OpenSSL Toolkit.
  [http://www.OpenSSL.org/](http://www.OpenSSL.org/)
* This product includes cryptographic software written by Eric Young
  (eay@cryptsoft.com)
* This product includes software written by Tim Hudson (tjh@cryptsoft.com)
