Merge pull request #6057 from zeha/combo-ipv6

[thirdparty/pdns.git] / pdns / recursordist / docs / settings.rst

PowerDNS Recursor Settings
==========================
Each setting can appear on the command line, prefixed by '--', or in the configuration file.
The command line overrides the configuration file.

**Note**: Settings marked as 'Boolean' can either be set to an empty value, which means on, or to 'no' or 'off' which means off.
Anything else means on.

As an example:

 - ``serve-rfc1918`` on its own means: do serve those zones.
 - ``serve-rfc1918=off`` or ``serve-rfc1918=no`` means: do not serve those zones.
 - Anything else means: do serve those zones.

.. _setting-aaaa-additional-processing:

``aaaa-additional-processing``
------------------------------
-  Boolean
-  Default: No

If turned on, the recursor will attempt to add AAAA IPv6 records to questions for MX records and NS records.
Can be quite slow as absence of these records in earlier answers does not guarantee their non-existence.
Can double the amount of queries needed.

.. _setting-allow-from:

``allow-from``
--------------
-  IP ranges, separated by commas
-  Default: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16

Netmasks (both IPv4 and IPv6) that are allowed to use the server.
The default allows access only from :rfc:`1918` private IP addresses.
Due to the aggressive nature of the internet these days, it is highly recommended to not open up the recursor for the entire internet.
Questions from IP addresses not listed here are ignored and do not get an answer.

.. _setting-allow-from-file:

``allow-from-file``
-------------------
-  Path

Like `allow-from`_, except reading from file.
Overrides the `allow-from`_ setting. To use this feature, supply one netmask per line, with optional comments preceded by a "#".

.. _setting-any-to-tcp:

``any-to-tcp``
--------------
-  Boolean
-  Default: no

Answer questions for the ANY type on UDP with a truncated packet that refers the remote server to TCP.
Useful for mitigating ANY reflection attacks.

.. _setting-api-config-dir:

``api-config-dir``
------------------
.. versionadded:: 4.0.0

-  Path
-  Default: unset

Directory where the REST API stores its configuration and zones.

.. _setting-api-key:

``api-key``
-----------
.. versionadded:: 4.0.0

-  String
-  Default: unset

Static pre-shared authentication key for access to the REST API.

.. _setting-api-readonly:

``api-readonly``
----------------
.. versionadded:: 4.0.0

-  Boolean
-  Default: no

Disallow data modification through the REST API when set.

.. _setting-api-logfile:

``api-logfile``
---------------
.. versionadded:: 4.0.0

-  Path
-  Default: unset

Location of the server logfile (used by the REST API).

.. _setting-auth-can-lower-ttl:

``auth-can-lower-ttl``
----------------------
-  Boolean
-  Default: no

Authoritative zones can transmit a TTL value that is lower than that specified in the parent zone.
This is called a 'delegation inconsistency'.
To follow :rfc:`RFC 2181 section 5.2<2181#section-5.2>` and :rfc:`5.4 <2181#section-5.4>` to the letter, enable this feature.
This will mean a slight deterioration of performance, and it will not solve any problems, but does make the recursor more standards compliant.
Not recommended unless you have to tick an 'RFC 2181 compliant' box.

.. _setting-auth-zones:

``auth-zones``
--------------
-  Comma separated list of 'zonename=filename' pairs

Zones read from these files (in BIND format) are served authoritatively.
DNSSEC is not supported. Example:

.. code-block:: none

    auth-zones=example.org=/var/zones/example.org, powerdns.com=/var/zones/powerdns.com

.. _setting-carbon-interval:

``carbon-interval``
-------------------
-  Integer
-  Default: 30

If sending carbon updates, this is the interval between them in seconds.
See :doc:`metrics`.

.. _setting-carbon-ourname:

``carbon-ourname``
------------------
-  String

If sending carbon updates, if set, this will override our hostname.
Be careful not to include any dots in this setting, unless you know what you are doing.
See :ref:`metricscarbon`.

.. _setting-carbon-server:

``carbon-server``
-----------------
-  IP address

If set to an IP or IPv6 address, will send all available metrics to this server via the carbon protocol, which is used by graphite and metronome.
You may specify an alternate port by appending :port, for example: ``127.0.0.1:2004``.
See :doc:`metrics`.

.. _setting-chroot:

``chroot``
----------
-  Path to a Directory

If set, chroot to this directory for more security.
See :doc:`security`

Make sure that ``/dev/log`` is available from within the chroot.
Logging will silently fail over time otherwise (on logrotate).

When using ``chroot``, all other paths (except for `config-dir`_) set in the configuration are relative to the new root.

When using ``chroot`` and the API (`webserver`_), `api-readonly`_ **must** be set and `api-config-dir`_ unset.

When running on a system where systemd manages services, ``chroot`` does not work out of the box, as PowerDNS cannot use the ``NOTIFY_SOCKET``.
Either do not ``chroot`` on these systems or set the 'Type' of this service to 'simple' instead of 'notify' (refer to the systemd documentation on how to modify unit-files).

.. _setting-client-tcp-timeout:

``client-tcp-timeout``
----------------------
-  Integer
-  Default: 2

Time to wait for data from TCP clients.

.. _setting-config-dir:

``config-dir``
--------------
-  Path

Location of configuration directory (``recursor.conf``).
Usually ``/etc/powerdns``, but this depends on ``SYSCONFDIR`` during compile-time.

.. _setting-config-name:

``config-name``
---------------
-  String
-  Default: unset

When running multiple recursors on the same server, read settings from :file:`recursor-{name}.conf`, this will also rename the binary image.

.. _setting-cpu-map:

``cpu-map``
-----------
.. versionadded:: 4.1.0

- String
- Default: unset

Set CPU affinity for worker threads, asking the scheduler to run those threads on a single CPU, or a set of CPUs.
This parameter accepts a space separated list of thread-id=cpu-id, or thread-id=cpu-id-1,cpu-id-2,...,cpu-id-N.
For example, to make the worker thread 0 run on CPU id 0 and the worker thread 1 on CPUs 1 and 2::

  cpu-map=0=0 1=1,2

The number of worker threads is determined by the :ref:`setting-threads` setting.
If :ref:`setting-pdns-distributes-queries` is set, an additional thread is started, assigned the id 0,
and is the only one listening on client sockets and accepting queries, distributing them to the other worker threads afterwards.

This parameter is only available on OS that provides the `pthread_setaffinity_np()` function.

.. _setting-daemon:

``daemon``
----------
-  Boolean
-  Default: no

.. versionchanged:: 4.0.0

    Default is now "no", was "yes" before.

Operate in the background.

.. _setting-delegation-only:

``delegation-only``
-------------------
-  Domains, comma separated

Which domains we only accept delegations from (a Verisign special).

.. _setting-disable-packetcache:

``disable-packetcache``
-----------------------
-  Boolean
-  Default: no

Turn off the packet cache. Useful when running with Lua scripts that can
not be cached.

.. _setting-disable-syslog:

``disable-syslog``
------------------
-  Boolean
-  Default: no

Do not log to syslog, only to stdout.
Use this setting when running inside a supervisor that handles logging (like systemd).
**Note**: do not use this setting in combination with `daemon`_ as all logging will disappear.

.. _setting-dnssec:

``dnssec``
----------
.. versionadded:: 4.0.0

-  One of ``off``, ``process-no-validate``, ``process``, ``log-fail``, ``validate``, String
-  Default: ``process-no-validate``

Set the mode for DNSSEC processing:

off
^^^
No DNSSEC processing whatsoever.
Ignore DO-bits in queries, don't request any DNSSEC information from authoritative servers.
This behaviour is similar to PowerDNS Recursor pre-4.0.

process-no-validate
^^^^^^^^^^^^^^^^^^^
Respond with DNSSEC records to clients that ask for it, set the DO bit on all outgoing queries.
Don't do any validation.

process
^^^^^^^
Respond with DNSSEC records to clients that ask for it, set the DO bit on all outgoing queries.
Do validation for clients that request it (by means of the AD- bit or DO-bit in the query).

log-fail
^^^^^^^^
Similar behaviour to ``process``, but validate RRSIGs on responses and log bogus responses.

validate
^^^^^^^^
Full blown DNSSEC validation. Send SERVFAIL to clients on bogus responses.

.. _setting-dnssec-log-bogus:

``dnssec-log-bogus``
--------------------
-  Boolean
-  Default: no

Log every DNSSEC validation failure.
**Note**: This is not logged per-query but every time records are validated as Bogus.

.. _setting-dont-query:

``dont-query``
--------------
-  Netmasks, comma separated
-  Default: 127.0.0.0/8, 10.0.0.0/8, 100.64.0.0/10, 169.254.0.0/16, 192.168.0.0/16, 172.16.0.0/12, ::1/128, fc00::/7, fe80::/10, 0.0.0.0/8, 192.0.0.0/24, 192.0.2.0/24, 198.51.100.0/24, 203.0.113.0/24, 240.0.0.0/4, ::/96, ::ffff:0:0/96, 100::/64, 2001:db8::/32

The DNS is a public database, but sometimes contains delegations to private IP addresses, like for example 127.0.0.1.
This can have odd effects, depending on your network, and may even be a security risk.
Therefore, the PowerDNS Recursor by default does not query private space IP addresses.
This setting can be used to expand or reduce the limitations.

Queries to addresses for zones as configured in any of the settings `forward-zones`_, `forward-zones-file`_ or `forward-zones-recurse`_ are performed regardless of these limitations.

.. _setting-ecs-ipv4-bits:

``ecs-ipv4-bits``
-----------------
.. versionadded:: 4.1.0

-  Integer
-  Default: 24

Number of bits of client IPv4 address to pass when sending EDNS Client Subnet address information.

.. _setting-ecs-ipv6-bits:

``ecs-ipv6-bits``
-----------------
.. versionadded:: 4.1.0

-  Integer
-  Default: 56

Number of bits of client IPv6 address to pass when sending EDNS Client Subnet address information.

.. _setting-ecs-scope-zero-address:

``ecs-scope-zero-address``
--------------------------
.. versionadded:: 4.1.0

- IPv4 or IPv6 Address
- Default: empty

The IP address sent via EDNS Client Subnet to authoritative servers listed in
`edns-subnet-whitelist`_ when `use-incoming-edns-subnet`_ is set and the query has
an ECS source prefix-length set to 0.
The default is to look for the first usable (not an ``any`` one) address in
`query-local-address`_ then `query-local-address6`_. If no suitable address is
found, the recursor fallbacks to sending 127.0.0.1.

.. _setting-edns-outgoing-bufsize:

``edns-outgoing-bufsize``
-------------------------
-  Integer
-  Default: 1680

This is the value set for the EDNS0 buffer size in outgoing packets.
Lower this if you experience timeouts.

.. _setting-edns-subnet-whitelist:

``edns-subnet-whitelist``
-------------------------
-  Comma separated list of domain names and netmasks
-  Default: (none)

List of netmasks and domains that :rfc:`EDNS Client Subnet <7871>` should be enabled for in outgoing queries.
For example, an EDNS Client Subnet option containing the address of the initial requestor will be added to an outgoing query sent to server 192.0.2.1 for domain X if 192.0.2.1 matches one of the supplied netmasks, or if X matches one of the supplied domains.
The initial requestor address will be truncated to 24 bits for IPv4 and to 56 bits for IPv6, as recommended in the privacy section of RFC 7871.
By default, this option is empty, meaning no EDNS Client Subnet information is sent.

.. _setting-entropy-source:

``entropy-source``
------------------
-  Path
-  Default: /dev/urandom

PowerDNS can read entropy from a (hardware) source.
This is used for generating random numbers which are very hard to predict.
Generally on UNIX platforms, this source will be ``/dev/urandom``, which will always supply random numbers, even if entropy is lacking.
Change to ``/dev/random`` if PowerDNS should block waiting for enough entropy to arrive.

.. _setting-etc-hosts-file:

``etc-hosts-file``
------------------
-  Path
-  Default: /etc/hosts

The path to the /etc/hosts file, or equivalent.
This file can be used to serve data authoritatively using `export-etc-hosts`_.

.. _setting-export-etc-hosts:

``export-etc-hosts``
--------------------
-  Boolean
-  Default: no

If set, this flag will export the host names and IP addresses mentioned in ``/etc/hosts``.

.. _setting-export-etc-hosts-search-suffix:

``export-etc-hosts-search-suffix``
----------------------------------
-  String

If set, all hostnames in the `export-etc-hosts`_ file are loaded in canonical form, based on this suffix, unless the name contains a '.', in which case the name is unchanged.
So an entry called 'pc' with ``export-etc-hosts-search-suffix='home.com'`` will lead to the generation of 'pc.home.com' within the recursor.
An entry called 'server1.home' will be stored as 'server1.home', regardless of this setting.

.. _setting-forward-zones:

``forward-zones``
-----------------
-  'zonename=IP' pairs, comma separated

Queries for zones listed here will be forwarded to the IP address listed. i.e. 

.. code-block:: none

    forward-zones=example.org=203.0.113.210, powerdns.com=2001:DB8::BEEF:5

Multiple IP addresses can be specified and port numbers other than 53 can be configured:

.. code-block:: none

    forward-zones=example.org=203.0.113.210:5300;127.0.0.1, powerdns.com=127.0.0.1;198.51.100.10:530;[2001:DB8::1:3]:5300

Forwarded queries have the 'recursion desired' bit set to 0, meaning that this setting is intended to forward queries to authoritative servers.

**IMPORTANT**: When using DNSSEC validation (which is default), forwards to non-delegated (e.g. internal) zones that have a DNSSEC signed parent zone will validate as Bogus.
To prevent this, add a Negative Trust Anchor (NTA) for this zone in the `lua-config-file`_ with ``addNTA("your.zone", "A comment")``.
If this forwarded zone is signed, instead of adding NTA, add the DS record to the `lua-config-file`_.
See the :doc:`dnssec` information.

.. _setting-forward-zones-file:

``forward-zones-file``
----------------------
-  Path

Same as `forward-zones`_, parsed from a file. Only 1 zone is allowed per line, specified as follows:

.. code-block:: none

    example.org=203.0.113.210, 192.0.2.4:5300

Zones prefixed with a '+' are forwarded with the recursion-desired bit set, for which see `forward-zones-recurse`_.
Default behaviour without '+' is as with `forward-zones`_.

.. versionchanged:: 4.0.0

  Comments are allowed, everything behind '#' is ignored.

The DNSSEC notes from `forward-zones`_ apply here as well.

.. _setting-forward-zones-recurse:

``forward-zones-recurse``
-------------------------
-  'zonename=IP' pairs, comma separated

Like regular `forward-zones`_, but forwarded queries have the 'recursion desired' bit set to 1, meaning that this setting is intended to forward queries to other recursive servers.

The DNSSEC notes from `forward-zones`_ apply here as well.

.. _setting-gettag-needs-edns-options:

``gettag-needs-edns-options``
-----------------------------
.. versionadded:: 4.1.0

-  Boolean
-  Default: no

If set, EDNS options in incoming queries are extracted and passed to the :func:`gettag` hook in the ``ednsoptions`` table.

.. _setting-hint-file:

``hint-file``
-------------
-  Path

If set, the root-hints are read from this file. If unset, default root hints are used.

.. _setting-include-dir:

``include-dir``
---------------
-  Path

Directory to scan for additional config files. All files that end with .conf are loaded in order using ``POSIX`` as locale.

.. _setting-latency-statistic-size:

``latency-statistic-size``
--------------------------
-  Integer
-  Default: 10000

Indication of how many queries will be averaged to get the average latency reported by the 'qa-latency' metric.

.. _setting-local-address:

``local-address``
-----------------
-  IP addresses, comma separated
-  Default: 127.0.0.1

Local IPv4 or IPv6 addresses to bind to.
Addresses can also contain port numbers, for IPv4 specify like this: ``192.0.2.4:5300``, for IPv6: ``[::1]:5300``.

**Warning**: When binding to wildcard addresses, UNIX semantics mean that answers may not be sent from the address a query was received on.
It is highly recommended to bind to explicit addresses.

.. _setting-local-port:

``local-port``
--------------
-  Integer
-  Default: 53

Local port to bind to.
If an address in `local-address`_ does not have an explicit port, this port is used.

.. _setting-log-timestamp:

``log-timestamp``
-----------------

.. versionadded:: 4.1.0

- Bool
- Default: yes

When printing log lines to stdout, prefix them with timestamps.
Disable this if the process supervisor timestamps these lines already.

.. note::
  The systemd unit file supplied with the source code already disables timestamp printing

.. _setting-non-local-bind:

``non-local-bind``
------------------
-  Boolean
-  Default: no

Bind to addresses even if one or more of the `local-address`_'s do not exist on this server.
Setting this option will enable the needed socket options to allow binding to non-local addresses.
This feature is intended to facilitate ip-failover setups, but it may also mask configuration issues and for this reason it is disabled by default.

.. _setting-loglevel:

``loglevel``
------------
-  Integer between 0 and 9
-  Default: 6

Amount of logging.
Higher is more, more logging may destroy performance.
It is recommended not to set this below 3.

.. _setting-log-common-errors:

``log-common-errors``
---------------------
-  Boolean
-  Default: no

Some DNS errors occur rather frequently and are no cause for alarm.

``log-rpz-changes``
---------------------
.. versionadded:: 4.1.0

-  Boolean
-  Default: no

Log additions and removals to RPZ zones at Info (6) level instead of Debug (7).

.. _setting-logging-facility:

``logging-facility``
--------------------
-  Integer

If set to a digit, logging is performed under this LOCAL facility.
See :ref:`logging`.
Do not pass names like 'local0'!

.. _setting-lowercase-outgoing:

``lowercase-outgoing``
----------------------
-  Boolean
-  Default: no

Set to true to lowercase the outgoing queries.
When set to 'no' (the default) a query from a client using mixed case in the DNS labels (such as a user entering mixed-case names or `draft-vixie-dnsext-dns0x20-00 <http://tools.ietf.org/html/draft-vixie-dnsext-dns0x20-00>`_), PowerDNS preserves the case of the query.
Broken authoritative servers might give a wrong or broken answer on this encoding.
Setting ``lowercase-outgoing`` to 'yes' makes the PowerDNS Recursor lowercase all the labels in the query to the authoritative servers, but still return the proper case to the client requesting.

.. _setting-lua-config-file:

``lua-config-file``
-------------------
-  Filename

If set, and Lua support is compiled in, this will load an additional configuration file for newer features and more complicated setups.
See :doc:`lua-config/index` for the options that can be set in this file.

.. _setting-lua-dns-script:

``lua-dns-script``
------------------
-  Path
-  Default: unset

Path to a lua file to manipulate the Recursor's answers. See :doc:`lua-scripting/index` for more information.

.. _setting-max-cache-entries:

``max-cache-entries``
---------------------
-  Integer
-  Default: 1000000

Maximum number of DNS cache entries.
1 million per thread will generally suffice for most installations.

.. _setting-max-cache-ttl:

``max-cache-ttl``
-----------------
-  Integer
-  Default: 86400

Maximum number of seconds to cache an item in the DNS cache, no matter what the original TTL specified.

.. versionchanged:: 4.1.0

    The minimum value of this setting is 15. i.e. setting this to lower than 15 will make this value 15.

.. _setting-max-mthreads:

``max-mthreads``
----------------
-  Integer
-  Default: 2048

Maximum number of simultaneous MTasker threads.

.. _setting-max-packetcache-entries:

``max-packetcache-entries``
---------------------------
-  Integer
-  Default: 500000

Maximum number of Packet Cache entries.
1 million per thread will generally suffice for most installations.

.. _setting-max-qperq:

``max-qperq``
-------------
-  Integer
-  Default: 50

The maximum number of outgoing queries that will be sent out during the resolution of a single client query.
This is used to limit endlessly chasing CNAME redirections.

.. _setting-max-negative-ttl:

``max-negative-ttl``
--------------------
-  Integer
-  Default: 3600

A query for which there is authoritatively no answer is cached to quickly deny a record's existence later on, without putting a heavy load on the remote server.
In practice, caches can become saturated with hundreds of thousands of hosts which are tried only once.
This setting, which defaults to 3600 seconds, puts a maximum on the amount of time negative entries are cached.

.. _setting-max-recursion-depth:

``max-recursion-depth``
-----------------------
-  Integer
-  Default: 40

Total maximum number of internal recursion calls the server may use to answer a single query.
0 means unlimited.
The value of `stack-size`_ should be increased together with this one to prevent the stack from overflowing.

.. versionchanged:: 4.1.0

    Before 4.1.0, this settings was unlimited.

.. _setting-max-tcp-clients:

``max-tcp-clients``
-------------------
-  Integer
-  Default: 128

Maximum number of simultaneous incoming TCP connections allowed.

.. _setting-max-tcp-per-client:

``max-tcp-per-client``
----------------------
-  Integer
-  Default: 0 (unlimited)

Maximum number of simultaneous incoming TCP connections allowed per client (remote IP address).

.. _setting-max-tcp-queries-per-connection:

``max-tcp-queries-per-connection``
----------------------------------
.. versionadded:: 4.1.0

-  Integer
-  Default: 0 (unlimited)

Maximum number of DNS queries in a TCP connection.

.. _setting-max-total-msec:

``max-total-msec``
------------------
-  Integer
-  Default: 7000

Total maximum number of milliseconds of wallclock time the server may use to answer a single query.

.. _setting-minimum-ttl-override:

``minimum-ttl-override``
------------------------
-  Integer
-  Default: 0 (disabled)

This setting artificially raises all TTLs to be at least this long.
While this is a gross hack, and violates RFCs, under conditions of DoS, it may enable you to continue serving your customers.
Can be set at runtime using ``rec_control set-minimum-ttl 3600``.

.. _setting-network-timeout:

``network-timeout``
-------------------
-  Integer
-  Default: 1500

Number of milliseconds to wait for a remote authoritative server to respond.

.. _setting-nsec3-max-iterations:

``nsec3-max-iterations``
------------------------
.. versionadded:: 4.1.0

-  Integer
-  Default: 2500

Maximum number of iterations allowed for an NSEC3 record.
If an answer containing an NSEC3 record with more iterations is received, its DNSSEC validation status is treated as Insecure.

.. _setting-packetcache-ttl:

``packetcache-ttl``
-------------------
-  Integer
-  Default: 3600

Maximum number of seconds to cache an item in the packet cache, no matter what the original TTL specified.

.. _setting-packetcache-servfail-ttl:

``packetcache-servfail-ttl``
----------------------------
-  Integer
-  Default: 60

Maximum number of seconds to cache a 'server failure' answer in the packet cache.

.. versionchanged:: 4.0.0

    This setting's maximum is capped to `packetcache-ttl`_.
    i.e. setting ``packetcache-ttl=15`` and keeping ``packetcache-servfail-ttl`` at the default will lower ``packetcache-servfail-ttl`` to ``15``.

.. _setting-pdns-distributes-queries:

``pdns-distributes-queries``
----------------------------
-  Boolean

If set, PowerDNS will have only 1 thread listening on client sockets, and distribute work by itself over threads.
Improves performance on Linux.

.. _setting-query-local-address:

``query-local-address``
-----------------------
-  IPv4 Address, comma separated
-  Default: 0.0.0.0

Send out local queries from this address, or addresses, by adding multiple addresses, increased spoofing resilience is achieved.

.. _setting-query-local-address6:

``query-local-address6``
------------------------
-  IPv6 addresses, comma separated
-  Default: unset

Send out local IPv6 queries from this address or addresses.
Disabled by default, which also disables outgoing IPv6 support.

.. _setting-quiet:

``quiet``
---------
-  Boolean
-  Default: yes

Don't log queries.

.. _setting-reuseport:

``reuseport``
-------------
-  Boolean
-  Default: no

If ``SO_REUSEPORT`` support is available, allows multiple processes to open a listening socket on the same port.

Since 4.1.0, when ``pdns-distributes-queries`` is set to false and ``reuseport`` is enabled, every thread will open a separate listening socket to let the kernel distribute the incoming queries, avoiding any thundering herd issue as well as the distributor thread being a bottleneck, thus leading to much higher performance on multi-core boxes.

.. _setting-root-nx-trust:

``root-nx-trust``
-----------------
-  Boolean
-  Default: yes

If set, an NXDOMAIN from the root-servers will serve as a blanket NXDOMAIN for the entire TLD the query belonged to.
The effect of this is far fewer queries to the root-servers.

.. versionchanged:: 4.0.0

    Default is 'yes' now, was 'no' before 4.0.0

.. _setting-security-poll-suffix:

``security-poll-suffix``
------------------------
-  String
-  Default: secpoll.powerdns.com.

Domain name from which to query security update notifications.
Setting this to an empty string disables secpoll.

.. _setting-serve-rfc1918:

``serve-rfc1918``
-----------------
-  Boolean
-  Default: yes

This makes the server authoritatively aware of: ``10.in-addr.arpa``, ``168.192.in-addr.arpa``, ``16-31.172.in-addr.arpa``, which saves load on the AS112 servers.
Individual parts of these zones can still be loaded or forwarded.

.. _setting-server-down-max-fails:

``server-down-max-fails``
-------------------------
-  Integer
-  Default: 64

If a server has not responded in any way this many times in a row, no longer send it any queries for `server-down-throttle-time`_ seconds.
Afterwards, we will try a new packet, and if that also gets no response at all, we again throttle for `server-down-throttle-time`_ seconds.
Even a single response packet will drop the block.

.. _setting-server-down-throttle-time:

``server-down-throttle-time``
-----------------------------
-  Integer
-  Default: 60

Throttle a server that has failed to respond `server-down-max-fails`_ times for this many seconds.

.. _setting-server-id:

``server-id``
-------------
-  String
-  Default: The hostname of the server

The PowerDNS recursor by replies to a query for 'id.server' with its hostname, useful for in clusters.
Use this setting to override the answer it gives.

Query example (where 192.0.2.14 is your server):

.. code-block:: sh

    dig @192.0.2.14 CHAOS TXT id.server.

``setgid``, ``setuid``
----------------------
-  String
-  Default: unset

PowerDNS can change its user and group id after binding to its socket.
Can be used for better :doc:`security <security>`.

.. _setting-single-socket:

``single-socket``
-----------------
-  Boolean
-  Default: no

Use only a single socket for outgoing queries.

.. _setting-snmp-agent:

``snmp-agent``
--------------
.. versionadded:: 4.1.0

-  Boolean
-  Default: no

If set to true and PowerDNS has been compiled with SNMP support, it will register as an SNMP agent to provide statistics and be able to send traps.

.. _setting-snmp-master-socket:

``snmp-master-socket``
----------------------
.. versionadded:: 4.1.0

-  String
-  Default: empty

If not empty and ``snmp-agent`` is set to true, indicates how PowerDNS should contact the SNMP master to register as an SNMP agent.

.. _setting-socket-dir:

``socket-dir``
--------------
-  Path

Where to store the control socket and pidfile.
The default depends on ``LOCALSTATEDIR`` during compile-time (usually ``/var/run`` or ``/run``).

When using `chroot`_ the default becomes to ``/``.

``socket-owner``, ``socket-group``, ``socket-mode``
---------------------------------------------------
Owner, group and mode of the controlsocket.
Owner and group can be specified by name, mode is in octal.

.. _setting-spoof-nearmiss-max:

``spoof-nearmiss-max``
----------------------
-  Integer
-  Default: 20

If set to non-zero, PowerDNS will assume it is being spoofed after seeing this many answers with the wrong id.

.. _setting-stack-size:

``stack-size``
--------------
-  Integer
-  Default: 200000

Size of the stack per thread.

.. _setting-statistics-interval:

``statistics-interval``
-----------------------
.. versionadded:: 4.1.0

-  Integer
-  Default: 1800

Interval between logging statistical summary on recursor performance.
Use 0 to disable.

.. _setting-stats-ringbuffer-entries:

``stats-ringbuffer-entries``
----------------------------
-  Integer
-  Default: 10000

Number of entries in the remotes ringbuffer, which keeps statistics on who is querying your server.
Can be read out using ``rec_control top-remotes``.

.. _setting-tcp-fast-open:

``tcp-fast-open``
-----------------
.. versionadded:: 4.1.0

-  Integer
-  Default: 0 (Disabled)

Enable TCP Fast Open support, if available, on the listening sockets.
The numerical value supplied is used as the queue size, 0 meaning disabled.

.. _setting-threads:

``threads``
-----------
-  Integer
-  Default: 2

Spawn this number of threads on startup.

.. _setting-trace:

``trace``
---------
-  Boolean
-  Default: no

If turned on, output impressive heaps of logging.
May destroy performance under load.

.. _setting-udp-truncation-threshold:

``udp-truncation-threshold``
----------------------------
-  Integer
-  Default: 1680

EDNS0 allows for large UDP response datagrams, which can potentially raise performance.
Large responses however also have downsides in terms of reflection attacks.
This setting limits the accepted size.
Maximum value is 65535, but values above 4096 should probably not be attempted.

.. _setting-use-incoming-edns-subnet:

``use-incoming-edns-subnet``
----------------------------
-  Boolean
-  Default: no

Whether to process and pass along a received EDNS Client Subnet to authoritative servers.
The ECS information will only be sent for netmasks and domains listed in `edns-subnet-whitelist`_ and will be truncated if the received scope exceeds `ecs-ipv4-bits`_ for IPv4 or `ecs-ipv6-bits`_ for IPv6.

.. _setting-version:

``version``
-----------
Print version of this binary. Useful for checking which version of the PowerDNS recursor is installed on a system.

.. _setting-version-string:

``version-string``
------------------
-  String
-  Default: PowerDNS Recursor version number

By default, PowerDNS replies to the 'version.bind' query with its version number.
Security conscious users may wish to override the reply PowerDNS issues.

.. _setting-webserver:

``webserver``
-------------
-  Boolean
-  Default: no

Start the webserver (for REST API).

.. _setting-webserver-address:

``webserver-address``
---------------------
-  IP Address
-  Default: 127.0.0.1

IP address for the webserver to listen on.

.. _setting-webserver-allow-from:

``webserver-allow-from``
------------------------
-  IP addresses, comma separated
-  Default: 127.0.0.1,::1

.. versionchanged:: 4.1.0

    Default is now 127.0.0.1,::1, was 0.0.0.0,::/0 before.

These subnets are allowed to access the webserver.

.. _setting-webserver-password:

``webserver-password``
----------------------
-  String
-  Default: unset

Password required to access the webserver.

.. _setting-webserver-port:

``webserver-port``
------------------
-  Integer
-  Default: 8082

TCP port where the webserver should listen on.

.. _setting-write-pid:

``write-pid``
-------------
-  Boolean
-  Default: yes

If a PID file should be written to `socket-dir`_