This document is about PowerDNS 4.X. If you have PowerDNS 3.X, please see the PowerDNS 3.X documentation

All 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.

So, as an example:

aaaa-additional-processing

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.

allow-from

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.

allow-from-file

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 #. Available since version 3.1.5.

any-to-tcp

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.

api-config-dir

Directory where the REST API stores its configuration and zones.

api-key

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

api-readonly

Disallow data modification through the REST API when set.

api-logfile

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

auth-can-lower-ttl

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 2181 paragraphs 5.2 and 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.

auth-zones

Zones read from these files (in BIND format) are served authoritatively. DNSSEC is not supported. Example: auth-zones=example.org=/var/zones/example.org, powerdns.com=/var/zones/powerdns.com.

statistics-interval

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

carbon-interval

If sending carbon updates, this is the interval between them in seconds. See "PowerDNS Metrics".

carbon-ourname

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 "PowerDNS Metrics".

carbon-server

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, ex: 127.0.0.1:2004. See "PowerDNS Metrics".

chroot

If set, chroot to this directory for more security. See 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)

client-tcp-timeout

Time to wait for data from TCP clients.

config-dir

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

config-name

When running multiple recursors on the same server, read settings from "recursor-name.conf", this will also rename the binary image.

daemon

Operate in the background.

delegation-only

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

disable-packetcache

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

disable-syslog

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.

dnssec

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.

dnssec-log-bogus

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

dont-query

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, since version 3.1.5, 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.

ecs-ipv4-bits

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

ecs-ipv6-bits

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

edns-outgoing-bufsize

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

edns-subnet-whitelist

List of netmasks and domains that EDNS Client Subnet 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.

entropy-source

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.

etc-hosts-file

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

export-etc-hosts

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

export-etc-hosts-search-suffix

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.

fork

If running on an SMP system with enough memory, this feature forks PowerDNS so it benefits from two processors. Experimental. Renames controlsockets, so care is needed to connect to the right one using rec_control, using socket-pid. Available in versions of the Recursor before 3.2, replaced by the 'threads' setting.

forward-zones

Queries for zones listed here will be forwarded to the IP address listed. i.e. forward-zones=example.org=203.0.113.210, powerdns.com=2001:DB8::BEEF:5.

Since version 3.1.5, multiple IP addresses can be specified. Additionally, port numbers other than 53 can be configured. Sample syntax: 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, or on the command line: --forward-zones="example.org=203.0.113.210:5300;127.0.0.1, powerdns.com=127.0.0.1;9.8.7.6:530;[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 recursor DNSSEC documentation for more information.

forward-zones-file

Same as forward-zones, parsed from a file. Only 1 zone is allowed per line, specified as follows: example.org=203.0.113.210, 192.0.2.4:5300.

Since version 3.2, zones prefixed with a '+' are forwarded with the recursion-desired bit set to one, for which see 'forward-zones-recurse'. Default behaviour without '+' is as with forward-zones.

Comments are allowed since version 4.0.0. Everything behind '#' is ignored.

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

forward-zones-recurse

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.

gettag-needs-edns-options

If set, EDNS options in incoming queries are extracted and passed to the gettag() hook in the ednsoptions table.

hint-file

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

include-dir

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

latency-statistic-size

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

local-address

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. Port specifications are available since version 3.1.2.

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.

local-port

Local port to bind to.

non-local-bind

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.

loglevel

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

log-common-errors

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

logging-facility

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

lowercase-outgoing

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), 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.

lua-config-file

If set, and Lua support is compiled in, this will load an additional configuration file for newer features and more complicated setups.

addSortList

Sortlist is a complicated feature which allows for the ordering of A and AAAA records in answers to be modified, optionally dependently on who is asking. Since clients frequently connect to the 'first' IP address they see, this can effectively allow you to make sure that user from, say 10.0.0.0/8 also preferably connect to servers in 10.0.0.0/8.

The syntax consists of a netmask for which this ordering instruction applies, followed by a set of netmask (groups) which describe the desired ordering. So an ordering instruction of "1.0.0.0/8", "2.0.0.0/8" will put anything within 1/8 first, and anything in 2/8 second. Other IP addresses would follow behind the addresses sorted earlier.

If netmasks are grouped, this means these get equal ordering.

addSortList() is intended to exactly mirror the semantics of the BIND sortlist option, but the syntax is slightly different.

As an example, the following BIND sortlist:

{ 17.50.0.0/16; {17.238.240.0/24; 17.138.149.200;
{17.218.242.254; 17.218.252.254;}; 17.38.42.80;
17.208.240.100; }; };

Gets transformed into:

addSortList("17.50.0.0/16", {"17.238.240.0/24", "17.138.149.200",
{"17.218.242.254", "17.218.252.254"}, "17.38.42.80", 
"17.208.240.100" })

In other words: each IP address is put within quotes, and are separated by commas instead of semicolons. For the rest everything is identical.

Response Policy Zone (RPZ)

Response Policy Zone is an open standard developed by Paul Vixie (ISC and Farsight) and Vernon Schryver (Rhyolite), to modify DNS responses based on a policy loaded via a zonefile.

Frequently, Response Policy Zones get to be very large and change quickly, so it is customary to update them over IXFR. It allows the use of third-party feeds, and near real-time policy updates.

An RPZ can be loaded from file or slaved from a master. To load from file, use for example:

rpzFile("dblfilename", {defpol=Policy.Custom, defcontent="badserver.example.com"})

To slave from a master and start IXFR to get updates, use for example:

rpzMaster("192.0.2.4", "policy.rpz", {defpol=Policy.Drop})

In this example, 'policy.rpz' denotes the name of the zone to query for.

Settings for rpzFile and rpzMaster can contain:

In addition to those, rpzMaster accepts:

If no settings are included, the RPZ is taken literally with no overrides applied.

The policy action are:

Protocol Buffers (protobuf)

PowerDNS Recursor has the ability to emit a stream of protocol buffers messages over TCP, containing information about queries, answers and policy decisions.

Messages contain the IP address of the client initiating the query, the one on which the message was received, whether it was received over UDP or TCP, a timestamp and the qname, qtype and qclass of the question. In addition, messages related to responses contain the name, type, class and rdata of A, AAAA and CNAME records present in the response, as well as the response code.

Finally, if a RPZ or custom Lua policy has been applied, response messages also contain the applied policy name and some tags. This is particularly useful to detect and act on infected hosts.

Protobuf export to a server is enabled using the protobufServer() directive:

protobufServer("192.0.2.1:4242" [[[[[[[, timeout], maxQueuedEntries], reconnectWaitTime], maskV4], maskV6], asyncConnect], taggedOnly])

The optional parameters are:

While protobufServer() only exports the queries sent to the recursor from clients, with the corresponding responses, outgoingProtobufServer() can be used to export outgoing queries sent by the recursor to authoritative servers, along with the corresponding responses.

outgoingProtobufServer("192.0.2.1:4242" [[[[, timeout], maxQueuedEntries], reconnectWaitTime], asyncConnect])

The optional parameters for outgoingProtobufServer() are:

The protocol buffers message types can be found in the dnsmessage.proto file.

lua-dns-script

Path to a lua file to manipulate the recursor's answers. See Scripting the recursor.

max-cache-entries

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

max-cache-ttl

Maximum number of seconds to cache an item in the DNS cache, no matter what the original TTL specified. Since PowerDNS Recursor 4.1.0, the minimum value of this setting is 15. i.e. setting this to lower than 15 will make this value 15.

max-mthreads

Maximum number of simultaneous MTasker threads.

max-packetcache-entries

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

max-qperq

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.

max-negative-ttl

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.

max-recursion-depth

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.

max-tcp-clients

Maximum number of simultaneous incoming TCP connections allowed.

max-tcp-per-client

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

max-tcp-queries-per-connection

Maximum number of DNS queries in a TCP connection.

max-total-msec

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

minimum-ttl-override

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.

network-timeout

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

packetcache-ttl

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

packetcache-servfail-ttl

Maximum number of seconds to cache a 'server failure' answer in the packet cache. From 4.0.0 onward, this settings 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.

pdns-distributes-queries

If set, PowerDNS will have only 1 thread listening on client sockets, and distribute work by itself over threads. Improves performance on Linux. Do not use on Recursor versions before 3.6 as the feature was experimental back then, and not that stable.

query-local-address

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

query-local-address6

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

quiet

Don't log queries.

reuseport

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.

root-nx-trust

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.

security-poll-suffix

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

serve-rfc1918

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.

server-down-max-fails

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.

server-down-throttle-time

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

server-id

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):

dig @192.0.2.14 CHAOS TXT id.server.

setgid, setuid

PowerDNS can change its user and group id after binding to its socket. Can be used for better security.

single-socket

Use only a single socket for outgoing queries.

snmp-agent

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.

snmp-master-socket

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

socket-dir

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.

spoof-nearmiss-max

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

stack-size

Size of the stack per thread.

stats-ringbuffer-entries

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.

tcp-fast-open

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

threads

Spawn this number of threads on startup.

trace

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

udp-truncation-threshold

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.

use-incoming-edns-subnet

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.

version

Print version of this binary. Useful for checking which version of the PowerDNS recursor is installed on a system. Available since version 3.1.5.

version-string

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

webserver

Start the webserver (for REST API).

webserver-address

IP address for the webserver to listen on.

webserver-allow-from

These subnets are allowed to access the webserver.

webserver-password

Password required to access the webserver.

webserver-port

TCP port where the webserver should listen on.

write-pid

If a PID file should be written. Available since 4.0.