unbound.conf(5) NLnet Labs unbound.conf(5)
unbound 1.19.3 unbound 1.19.3
Mar 14, 2024
NAME
unbound.conf - Unbound configuration file.
SYNOPSIS
unbound.conf
DESCRIPTION
unbound.conf is used to configure unbound(8). The file format has
attributes and values. Some attributes have attributes inside them.
The notation is: attribute: value.
Comments start with # and last to the end of line. Empty lines are
ignored as is whitespace at the beginning of a line.
The utility unbound-checkconf(8) can be used to check unbound.conf
prior to usage.
EXAMPLE
An example config file is shown below. Copy this to
/etc/unbound/unbound.conf and start the server with:
$ unbound -c /etc/unbound/unbound.conf
Most settings are the defaults. Stop the server with:
$ kill `cat /etc/unbound/unbound.pid`
Below is a minimal config file. The source distribution contains an
extensive example.conf file with all the options.
# unbound.conf(5) config file for unbound(8).
server:
directory: "/etc/unbound"
username: unbound
# make sure unbound can access entropy from inside the chroot.
# e.g. on linux the use these commands (on BSD, devfs(8) is used):
# mount --bind -n /dev/urandom /etc/unbound/dev/urandom
# and mount --bind -n /dev/log /etc/unbound/dev/log
chroot: "/etc/unbound"
# logfile: "/etc/unbound/unbound.log" #uncomment to use logfile.
pidfile: "/etc/unbound/unbound.pid"
# verbosity: 1 # uncomment and increase to get more logging.
# listen on all interfaces, answer queries from the local subnet.
interface: 0.0.0.0
interface: ::0
access-control: 10.0.0.0/8 allow
access-control: 2001:DB8::/64 allow
FILE FORMAT
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There must be whitespace between keywords. Attribute keywords end
with a colon ':'. An attribute is followed by a value, or its
containing attributes in which case it is referred to as a clause.
Clauses can be repeated throughout the file (or included files) to
group attributes under the same clause.
Files can be included using the include: directive. It can appear
anywhere, it accepts a single file name as argument. Processing
continues as if the text from the included file was copied into the
config file at that point. If also using chroot, using full path
names for the included files works, relative pathnames for the
included names work if the directory where the daemon is started
equals its chroot/working directory or is specified before the include
statement with directory: dir. Wildcards can be used to include
multiple files, see glob(7).
For a more structural include option, the include-toplevel: directive
can be used. This closes whatever clause is currently active (if any)
and forces the use of clauses in the included files and right after
this directive.
Server Options
These options are part of the server: clause.
verbosity: <number>
The verbosity number, level 0 means no verbosity, only errors.
Level 1 gives operational information. Level 2 gives detailed
operational information including short information per query.
Level 3 gives query level information, output per query. Level 4
gives algorithm level information. Level 5 logs client
identification for cache misses. Default is level 1. The
verbosity can also be increased from the commandline, see
unbound(8).
statistics-interval: <seconds>
The number of seconds between printing statistics to the log for
every thread. Disable with value 0 or "". Default is disabled.
The histogram statistics are only printed if replies were sent
during the statistics interval, requestlist statistics are
printed for every interval (but can be 0). This is because the
median calculation requires data to be present.
statistics-cumulative: <yes or no>
If enabled, statistics are cumulative since starting Unbound,
without clearing the statistics counters after logging the
statistics. Default is no.
extended-statistics: <yes or no>
If enabled, extended statistics are printed from
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unbound-control(8). Default is off, because keeping track of
more statistics takes time. The counters are listed in
unbound-control(8).
statistics-inhibit-zero: <yes or no>
If enabled, selected extended statistics with a value of 0 are
inhibited from printing with unbound-control(8). These are query
types, query classes, query opcodes, answer rcodes (except
NOERROR, FORMERR, SERVFAIL, NXDOMAIN, NOTIMPL, REFUSED) and RPZ
actions. Default is on.
num-threads: <number>
The number of threads to create to serve clients. Use 1 for no
threading.
port: <port number>
The port number, default 53, on which the server responds to
queries.
interface: <ip address or interface name
Interface to use to connect to the network. This interface is
listened to for queries from clients, and answers to clients are
given from it. Can be given multiple times to work on several
interfaces. If none are given the default is to listen to
localhost. If an interface name is used instead of an ip
address, the list of ip addresses on that interface are used.
The interfaces are not changed on a reload (kill -HUP) but only
on restart. A port number can be specified with @port (without
spaces between interface and port number), if not specified the
default port (from port) is used.
ip-address: <ip address or interface name
Same as interface: (for ease of compatibility with nsd.conf).
interface-automatic: <yes or no>
Listen on all addresses on all (current and future) interfaces,
detect the source interface on UDP queries and copy them to
replies. This is a lot like ip-transparent, but this option
services all interfaces whilst with ip-transparent you can select
which (future) interfaces Unbound provides service on. This
feature is experimental, and needs support in your OS for
particular socket options. Default value is no.
interface-automatic-ports: <string>
List the port numbers that interface-automatic listens on. If
empty, the default port is listened on. The port numbers are
separated by spaces in the string. Default is "".
This can be used to have interface automatic to deal with the
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interface, and listen on the normal port number, by including it
in the list, and also https or dns over tls port numbers by
putting them in the list as well.
outgoing-interface: <ip address or ip6 netblock>
Interface to use to connect to the network. This interface is
used to send queries to authoritative servers and receive their
replies. Can be given multiple times to work on several
interfaces. If none are given the default (all) is used. You can
specify the same interfaces in interface: and outgoing-interface:
lines, the interfaces are then used for both purposes. Outgoing
queries are sent via a random outgoing interface to counter
spoofing.
If an IPv6 netblock is specified instead of an individual IPv6
address, outgoing UDP queries will use a randomised source
address taken from the netblock to counter spoofing. Requires the
IPv6 netblock to be routed to the host running Unbound, and
requires OS support for unprivileged non-local binds (currently
only supported on Linux). Several netblocks may be specified with
multiple outgoing-interface: options, but do not specify both an
individual IPv6 address and an IPv6 netblock, or the
randomisation will be compromised. Consider combining with
prefer-ip6: yes to increase the likelihood of IPv6 nameservers
being selected for queries. On Linux you need these two commands
to be able to use the freebind socket option to receive traffic
for the ip6 netblock: ip -6 addr add mynetblock/64 dev lo && ip
-6 route add local mynetblock/64 dev lo
outgoing-range: <number>
Number of ports to open. This number of file descriptors can be
opened per thread. Must be at least 1. Default depends on compile
options. Larger numbers need extra resources from the operating
system. For performance a very large value is best, use libevent
to make this possible.
outgoing-port-permit: <port number or range>
Permit Unbound to open this port or range of ports for use to
send queries. A larger number of permitted outgoing ports
increases resilience against spoofing attempts. Make sure these
ports are not needed by other daemons. By default only ports
above 1024 that have not been assigned by IANA are used. Give a
port number or a range of the form "low-high", without spaces.
The outgoing-port-permit and outgoing-port-avoid statements are
processed in the line order of the config file, adding the
permitted ports and subtracting the avoided ports from the set of
allowed ports. The processing starts with the non IANA allocated
ports above 1024 in the set of allowed ports.
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outgoing-port-avoid: <port number or range>
Do not permit Unbound to open this port or range of ports for use
to send queries. Use this to make sure Unbound does not grab a
port that another daemon needs. The port is avoided on all
outgoing interfaces, both IP4 and IP6. By default only ports
above 1024 that have not been assigned by IANA are used. Give a
port number or a range of the form "low-high", without spaces.
outgoing-num-tcp: <number>
Number of outgoing TCP buffers to allocate per thread. Default is
10. If set to 0, or if do-tcp is "no", no TCP queries to
authoritative servers are done. For larger installations
increasing this value is a good idea.
incoming-num-tcp: <number>
Number of incoming TCP buffers to allocate per thread. Default is
10. If set to 0, or if do-tcp is "no", no TCP queries from
clients are accepted. For larger installations increasing this
value is a good idea.
edns-buffer-size: <number>
Number of bytes size to advertise as the EDNS reassembly buffer
size. This is the value put into datagrams over UDP towards
peers. The actual buffer size is determined by msg-buffer-size
(both for TCP and UDP). Do not set higher than that value.
Default is 1232 which is the DNS Flag Day 2020 recommendation.
Setting to 512 bypasses even the most stringent path MTU
problems, but is seen as extreme, since the amount of TCP
fallback generated is excessive (probably also for this resolver,
consider tuning the outgoing tcp number).
max-udp-size: <number>
Maximum UDP response size (not applied to TCP response). 65536
disables the udp response size maximum, and uses the choice from
the client, always. Suggested values are 512 to 4096. Default is
1232. The default value is the same as the default for
edns-buffer-size.
stream-wait-size: <number>
Number of bytes size maximum to use for waiting stream buffers.
Default is 4 megabytes. A plain number is in bytes, append 'k',
'm' or 'g' for kilobytes, megabytes or gigabytes (1024*1024 bytes
in a megabyte). As TCP and TLS streams queue up multiple
results, the amount of memory used for these buffers does not
exceed this number, otherwise the responses are dropped. This
manages the total memory usage of the server (under heavy use),
the number of requests that can be queued up per connection is
also limited, with further requests waiting in TCP buffers.
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msg-buffer-size: <number>
Number of bytes size of the message buffers. Default is 65552
bytes, enough for 64 Kb packets, the maximum DNS message size. No
message larger than this can be sent or received. Can be reduced
to use less memory, but some requests for DNS data, such as for
huge resource records, will result in a SERVFAIL reply to the
client.
msg-cache-size: <number>
Number of bytes size of the message cache. Default is 4
megabytes. A plain number is in bytes, append 'k', 'm' or 'g'
for kilobytes, megabytes or gigabytes (1024*1024 bytes in a
megabyte).
msg-cache-slabs: <number>
Number of slabs in the message cache. Slabs reduce lock
contention by threads. Must be set to a power of 2. Setting
(close) to the number of cpus is a reasonable guess.
num-queries-per-thread: <number>
The number of queries that every thread will service
simultaneously. If more queries arrive that need servicing, and
no queries can be jostled out (see jostle-timeout), then the
queries are dropped. This forces the client to resend after a
timeout; allowing the server time to work on the existing
queries. Default depends on compile options, 512 or 1024.
jostle-timeout: <msec>
Timeout used when the server is very busy. Set to a value that
usually results in one roundtrip to the authority servers. If
too many queries arrive, then 50% of the queries are allowed to
run to completion, and the other 50% are replaced with the new
incoming query if they have already spent more than their allowed
time. This protects against denial of service by slow queries or
high query rates. Default 200 milliseconds. The effect is that
the qps for long-lasting queries is about (numqueriesperthread /
2) / (average time for such long queries) qps. The qps for short
queries can be about (numqueriesperthread / 2) / (jostletimeout
in whole seconds) qps per thread, about (1024/2)*5 = 2560 qps by
default.
delay-close: <msec>
Extra delay for timeouted UDP ports before they are closed, in
msec. Default is 0, and that disables it. This prevents very
delayed answer packets from the upstream (recursive) servers from
bouncing against closed ports and setting off all sort of close-
port counters, with eg. 1500 msec. When timeouts happen you need
extra sockets, it checks the ID and remote IP of packets, and
unwanted packets are added to the unwanted packet counter.
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udp-connect: <yes or no>
Perform connect for UDP sockets that mitigates ICMP side channel
leakage. Default is yes.
unknown-server-time-limit: <msec>
The wait time in msec for waiting for an unknown server to reply.
Increase this if you are behind a slow satellite link, to eg.
1128. That would then avoid re-querying every initial query
because it times out. Default is 376 msec.
so-rcvbuf: <number>
If not 0, then set the SO_RCVBUF socket option to get more buffer
space on UDP port 53 incoming queries. So that short spikes on
busy servers do not drop packets (see counter in netstat -su).
Default is 0 (use system value). Otherwise, the number of bytes
to ask for, try "4m" on a busy server. The OS caps it at a
maximum, on linux Unbound needs root permission to bypass the
limit, or the admin can use sysctl net.core.rmem_max. On BSD
change kern.ipc.maxsockbuf in /etc/sysctl.conf. On OpenBSD
change header and recompile kernel. On Solaris ndd -set /dev/udp
udp_max_buf 8388608.
so-sndbuf: <number>
If not 0, then set the SO_SNDBUF socket option to get more buffer
space on UDP port 53 outgoing queries. This for very busy
servers handles spikes in answer traffic, otherwise 'send:
resource temporarily unavailable' can get logged, the buffer
overrun is also visible by netstat -su. Default is 0 (use system
value). Specify the number of bytes to ask for, try "4m" on a
very busy server. The OS caps it at a maximum, on linux Unbound
needs root permission to bypass the limit, or the admin can use
sysctl net.core.wmem_max. On BSD, Solaris changes are similar to
so-rcvbuf.
so-reuseport: <yes or no>
If yes, then open dedicated listening sockets for incoming
queries for each thread and try to set the SO_REUSEPORT socket
option on each socket. May distribute incoming queries to
threads more evenly. Default is yes. On Linux it is supported
in kernels >= 3.9. On other systems, FreeBSD, OSX it may also
work. You can enable it (on any platform and kernel), it then
attempts to open the port and passes the option if it was
available at compile time, if that works it is used, if it fails,
it continues silently (unless verbosity 3) without the option.
At extreme load it could be better to turn it off to distribute
the queries evenly, reported for Linux systems (4.4.x).
ip-transparent: <yes or no>
If yes, then use IP_TRANSPARENT socket option on sockets where
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Unbound is listening for incoming traffic. Default no. Allows
you to bind to non-local interfaces. For example for
non-existent IP addresses that are going to exist later on, with
host failover configuration. This is a lot like
interface-automatic, but that one services all interfaces and
with this option you can select which (future) interfaces Unbound
provides service on. This option needs Unbound to be started
with root permissions on some systems. The option uses
IP_BINDANY on FreeBSD systems and SO_BINDANY on OpenBSD systems.
ip-freebind: <yes or no>
If yes, then use IP_FREEBIND socket option on sockets where
Unbound is listening to incoming traffic. Default no. Allows
you to bind to IP addresses that are nonlocal or do not exist,
like when the network interface or IP address is down. Exists
only on Linux, where the similar ip-transparent option is also
available.
ip-dscp: <number>
The value of the Differentiated Services Codepoint (DSCP) in the
differentiated services field (DS) of the outgoing IP packet
headers. The field replaces the outdated IPv4 Type-Of-Service
field and the IPv6 traffic class field.
rrset-cache-size: <number>
Number of bytes size of the RRset cache. Default is 4 megabytes.
A plain number is in bytes, append 'k', 'm' or 'g' for kilobytes,
megabytes or gigabytes (1024*1024 bytes in a megabyte).
rrset-cache-slabs: <number>
Number of slabs in the RRset cache. Slabs reduce lock contention
by threads. Must be set to a power of 2.
cache-max-ttl: <seconds>
Time to live maximum for RRsets and messages in the cache.
Default is 86400 seconds (1 day). When the TTL expires, the
cache item has expired. Can be set lower to force the resolver
to query for data often, and not trust (very large) TTL values.
Downstream clients also see the lower TTL.
cache-min-ttl: <seconds>
Time to live minimum for RRsets and messages in the cache.
Default is 0. If the minimum kicks in, the data is cached for
longer than the domain owner intended, and thus less queries are
made to look up the data. Zero makes sure the data in the cache
is as the domain owner intended, higher values, especially more
than an hour or so, can lead to trouble as the data in the cache
does not match up with the actual data any more.
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cache-max-negative-ttl: <seconds>
Time to live maximum for negative responses, these have a SOA in
the authority section that is limited in time. Default is 3600.
This applies to nxdomain and nodata answers.
infra-host-ttl: <seconds>
Time to live for entries in the host cache. The host cache
contains roundtrip timing, lameness and EDNS support information.
Default is 900.
infra-cache-slabs: <number>
Number of slabs in the infrastructure cache. Slabs reduce lock
contention by threads. Must be set to a power of 2.
infra-cache-numhosts: <number>
Number of hosts for which information is cached. Default is
10000.
infra-cache-min-rtt: <msec>
Lower limit for dynamic retransmit timeout calculation in
infrastructure cache. Default is 50 milliseconds. Increase this
value if using forwarders needing more time to do recursive name
resolution.
infra-cache-max-rtt: <msec>
Upper limit for dynamic retransmit timeout calculation in
infrastructure cache. Default is 2 minutes.
infra-keep-probing: <yes or no>
If enabled the server keeps probing hosts that are down, in the
one probe at a time regime. Default is no. Hosts that are down,
eg. they did not respond during the one probe at a time period,
are marked as down and it may take infra-host-ttl time to get
probed again.
define-tag: <"list of tags">
Define the tags that can be used with local-zone and
access-control. Enclose the list between quotes ("") and put
spaces between tags.
do-ip4: <yes or no>
Enable or disable whether ip4 queries are answered or issued.
Default is yes.
do-ip6: <yes or no>
Enable or disable whether ip6 queries are answered or issued.
Default is yes. If disabled, queries are not answered on IPv6,
and queries are not sent on IPv6 to the internet nameservers.
With this option you can disable the IPv6 transport for sending
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DNS traffic, it does not impact the contents of the DNS traffic,
which may have ip4 and ip6 addresses in it.
prefer-ip4: <yes or no>
If enabled, prefer IPv4 transport for sending DNS queries to
internet nameservers. Default is no. Useful if the IPv6 netblock
the server has, the entire /64 of that is not owned by one
operator and the reputation of the netblock /64 is an issue,
using IPv4 then uses the IPv4 filters that the upstream servers
have.
prefer-ip6: <yes or no>
If enabled, prefer IPv6 transport for sending DNS queries to
internet nameservers. Default is no.
do-udp: <yes or no>
Enable or disable whether UDP queries are answered or issued.
Default is yes.
do-tcp: <yes or no>
Enable or disable whether TCP queries are answered or issued.
Default is yes.
tcp-mss: <number>
Maximum segment size (MSS) of TCP socket on which the server
responds to queries. Value lower than common MSS on Ethernet
(1220 for example) will address path MTU problem. Note that not
all platform supports socket option to set MSS (TCP_MAXSEG).
Default is system default MSS determined by interface MTU and
negotiation between server and client.
outgoing-tcp-mss: <number>
Maximum segment size (MSS) of TCP socket for outgoing queries
(from Unbound to other servers). Value lower than common MSS on
Ethernet (1220 for example) will address path MTU problem. Note
that not all platform supports socket option to set MSS
(TCP_MAXSEG). Default is system default MSS determined by
interface MTU and negotiation between Unbound and other servers.
tcp-idle-timeout: <msec>
The period Unbound will wait for a query on a TCP connection. If
this timeout expires Unbound closes the connection. This option
defaults to 30000 milliseconds. When the number of free incoming
TCP buffers falls below 50% of the total number configured, the
option value used is progressively reduced, first to 1% of the
configured value, then to 0.2% of the configured value if the
number of free buffers falls below 35% of the total number
configured, and finally to 0 if the number of free buffers falls
below 20% of the total number configured. A minimum timeout of
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200 milliseconds is observed regardless of the option value used.
tcp-reuse-timeout: <msec>
The period Unbound will keep TCP persistent connections open to
authority servers. This option defaults to 60000 milliseconds.
max-reuse-tcp-queries: <number>
The maximum number of queries that can be sent on a persistent
TCP connection. This option defaults to 200 queries.
tcp-auth-query-timeout: <number>
Timeout in milliseconds for TCP queries to auth servers. This
option defaults to 3000 milliseconds.
edns-tcp-keepalive: <yes or no>
Enable or disable EDNS TCP Keepalive. Default is no.
edns-tcp-keepalive-timeout: <msec>
The period Unbound will wait for a query on a TCP connection when
EDNS TCP Keepalive is active. If this timeout expires Unbound
closes the connection. If the client supports the EDNS TCP
Keepalive option, Unbound sends the timeout value to the client
to encourage it to close the connection before the server times
out. This option defaults to 120000 milliseconds. When the
number of free incoming TCP buffers falls below 50% of the total
number configured, the advertised timeout is progressively
reduced to 1% of the configured value, then to 0.2% of the
configured value if the number of free buffers falls below 35% of
the total number configured, and finally to 0 if the number of
free buffers falls below 20% of the total number configured. A
minimum actual timeout of 200 milliseconds is observed regardless
of the advertised timeout.
sock-queue-timeout: <sec>
UDP queries that have waited in the socket buffer for a long time
can be dropped. Default is 0, disabled. The time is set in
seconds, 3 could be a good value to ignore old queries that
likely the client does not need a reply for any more. This could
happen if the host has not been able to service the queries for a
while, i.e. Unbound is not running, and then is enabled again. It
uses timestamp socket options.
tcp-upstream: <yes or no>
Enable or disable whether the upstream queries use TCP only for
transport. Default is no. Useful in tunneling scenarios. If set
to no you can specify TCP transport only for selected forward or
stub zones using forward-tcp-upstream or stub-tcp-upstream
respectively.
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udp-upstream-without-downstream: <yes or no>
Enable udp upstream even if do-udp is no. Default is no, and
this does not change anything. Useful for TLS service providers,
that want no udp downstream but use udp to fetch data upstream.
tls-upstream: <yes or no>
Enabled or disable whether the upstream queries use TLS only for
transport. Default is no. Useful in tunneling scenarios. The
TLS contains plain DNS in TCP wireformat. The other server must
support this (see tls-service-key). If you enable this, also
configure a tls-cert-bundle or use tls-win-cert or
tls-system-cert to load CA certs, otherwise the connections
cannot be authenticated. This option enables TLS for all of them,
but if you do not set this you can configure TLS specifically for
some forward zones with forward-tls-upstream. And also with
stub-tls-upstream.
ssl-upstream: <yes or no>
Alternate syntax for tls-upstream. If both are present in the
config file the last is used.
tls-service-key: <file>
If enabled, the server provides DNS-over-TLS or DNS-over-HTTPS
service on the TCP ports marked implicitly or explicitly for
these services with tls-port or https-port. The file must contain
the private key for the TLS session, the public certificate is in
the tls-service-pem file and it must also be specified if
tls-service-key is specified. The default is "", turned off.
Enabling or disabling this service requires a restart (a reload
is not enough), because the key is read while root permissions
are held and before chroot (if any). The ports enabled
implicitly or explicitly via tls-port: and https-port: do not
provide normal DNS TCP service. Unbound needs to be compiled with
libnghttp2 in order to provide DNS-over-HTTPS.
ssl-service-key: <file>
Alternate syntax for tls-service-key.
tls-service-pem: <file>
The public key certificate pem file for the tls service. Default
is "", turned off.
ssl-service-pem: <file>
Alternate syntax for tls-service-pem.
tls-port: <number>
The port number on which to provide TCP TLS service, default 853,
only interfaces configured with that port number as @number get
the TLS service.
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ssl-port: <number>
Alternate syntax for tls-port.
tls-cert-bundle: <file>
If null or "", no file is used. Set it to the certificate bundle
file, for example "/etc/pki/tls/certs/ca-bundle.crt". These
certificates are used for authenticating connections made to
outside peers. For example auth-zone urls, and also DNS over TLS
connections. It is read at start up before permission drop and
chroot.
ssl-cert-bundle: <file>
Alternate syntax for tls-cert-bundle.
tls-win-cert: <yes or no>
Add the system certificates to the cert bundle certificates for
authentication. If no cert bundle, it uses only these
certificates. Default is no. On windows this option uses the
certificates from the cert store. Use the tls-cert-bundle option
on other systems. On other systems, this option enables the
system certificates.
tls-system-cert: <yes or no>
This the same setting as the tls-win-cert setting, under a
different name. Because it is not windows specific.
tls-additional-port: <portnr>
List portnumbers as tls-additional-port, and when interfaces are
defined, eg. with the @port suffix, as this port number, they
provide dns over TLS service. Can list multiple, each on a new
statement.
tls-session-ticket-keys: <file>
If not "", lists files with 80 bytes of random contents that are
used to perform TLS session resumption for clients using the
Unbound server. These files contain the secret key for the TLS
session tickets. First key use to encrypt and decrypt TLS
session tickets. Other keys use to decrypt only. With this you
can roll over to new keys, by generating a new first file and
allowing decrypt of the old file by listing it after the first
file for some time, after the wait clients are not using the old
key any more and the old key can be removed. One way to create
the file is dd if=/dev/random bs=1 count=80 of=ticket.dat The
first 16 bytes should be different from the old one if you create
a second key, that is the name used to identify the key. Then
there is 32 bytes random data for an AES key and then 32 bytes
random data for the HMAC key.
tls-ciphers: <string with cipher list>
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Set the list of ciphers to allow when serving TLS. Use "" for
defaults, and that is the default.
tls-ciphersuites: <string with ciphersuites list>
Set the list of ciphersuites to allow when serving TLS. This is
for newer TLS 1.3 connections. Use "" for defaults, and that is
the default.
pad-responses: <yes or no>
If enabled, TLS serviced queries that contained an EDNS Padding
option will cause responses padded to the closest multiple of the
size specified in pad-responses-block-size. Default is yes.
pad-responses-block-size: <number>
The block size with which to pad responses serviced over TLS.
Only responses to padded queries will be padded. Default is 468.
pad-queries: <yes or no>
If enabled, all queries sent over TLS upstreams will be padded to
the closest multiple of the size specified in
pad-queries-block-size. Default is yes.
pad-queries-block-size: <number>
The block size with which to pad queries sent over TLS upstreams.
Default is 128.
tls-use-sni: <yes or no>
Enable or disable sending the SNI extension on TLS connections.
Default is yes. Changing the value requires a reload.
https-port: <number>
The port number on which to provide DNS-over-HTTPS service,
default 443, only interfaces configured with that port number as
@number get the HTTPS service.
http-endpoint: <endpoint string>
The HTTP endpoint to provide DNS-over-HTTPS service on. Default
"/dns-query".
http-max-streams: <number of streams>
Number used in the SETTINGS_MAX_CONCURRENT_STREAMS parameter in
the HTTP/2 SETTINGS frame for DNS-over-HTTPS connections. Default
100.
http-query-buffer-size: <size in bytes>
Maximum number of bytes used for all HTTP/2 query buffers
combined. These buffers contain (partial) DNS queries waiting for
request stream completion. An RST_STREAM frame will be send to
streams exceeding this limit. Default is 4 megabytes. A plain
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number is in bytes, append 'k', 'm' or 'g' for kilobytes,
megabytes or gigabytes (1024*1024 bytes in a megabyte).
http-response-buffer-size: <size in bytes>
Maximum number of bytes used for all HTTP/2 response buffers
combined. These buffers contain DNS responses waiting to be
written back to the clients. An RST_STREAM frame will be send to
streams exceeding this limit. Default is 4 megabytes. A plain
number is in bytes, append 'k', 'm' or 'g' for kilobytes,
megabytes or gigabytes (1024*1024 bytes in a megabyte).
http-nodelay: <yes or no>
Set TCP_NODELAY socket option on sockets used to provide DNS-
over-HTTPS service. Ignored if the option is not available.
Default is yes.
http-notls-downstream: <yes or no>
Disable use of TLS for the downstream DNS-over-HTTP connections.
Useful for local back end servers. Default is no.
proxy-protocol-port: <portnr>
List port numbers as proxy-protocol-port, and when interfaces are
defined, eg. with the @port suffix, as this port number, they
support and expect PROXYv2. In this case the proxy address will
only be used for the network communication and initial ACL (check
if the proxy itself is denied/refused by configuration). The
proxied address (if any) will then be used as the true client
address and will be used where applicable for logging, ACL,
DNSTAP, RPZ and IP ratelimiting. PROXYv2 is supported for UDP
and TCP/TLS listening interfaces. There is no support for
PROXYv2 on a DoH or DNSCrypt listening interface. Can list
multiple, each on a new statement.
use-systemd: <yes or no>
Enable or disable systemd socket activation. Default is no.
do-daemonize: <yes or no>
Enable or disable whether the Unbound server forks into the
background as a daemon. Set the value to no when Unbound runs as
systemd service. Default is yes.
tcp-connection-limit: <IP netblock> <limit>
Allow up to limit simultaneous TCP connections from the given
netblock. When at the limit, further connections are accepted
but closed immediately. This option is experimental at this
time.
access-control: <IP netblock> <action>
Specify treatment of incoming queries from their originating IP
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address. Queries can be allowed to have access to this server
that gives DNS answers, or refused, with other actions possible.
The IP address range can be specified as a netblock, it is
possible to give the statement several times in order to specify
the treatment of different netblocks.
The netblock is given as an IP4 or IP6 address with /size
appended for a classless network block. The action can be deny,
refuse, allow, allow_setrd, allow_snoop, allow_cookie,
deny_non_local or refuse_non_local. The most specific netblock
match is used, if none match refuse is used. The order of the
access-control statements therefore does not matter.
The deny action stops queries from hosts from that netblock.
The refuse action stops queries too, but sends a DNS rcode
REFUSED error message back.
The allow action gives access to clients from that netblock. It
gives only access for recursion clients (which is what almost all
clients need). Nonrecursive queries are refused.
The allow action does allow nonrecursive queries to access the
local-data that is configured. The reason is that this does not
involve the Unbound server recursive lookup algorithm, and static
data is served in the reply. This supports normal operations
where nonrecursive queries are made for the authoritative data.
For nonrecursive queries any replies from the dynamic cache are
refused.
The allow_setrd action ignores the recursion desired (RD) bit and
treats all requests as if the recursion desired bit is set. Note
that this behavior violates RFC 1034 which states that a name
server should never perform recursive service unless asked via
the RD bit since this interferes with trouble shooting of name
servers and their databases. This prohibited behavior may be
useful if another DNS server must forward requests for specific
zones to a resolver DNS server, but only supports stub domains
and sends queries to the resolver DNS server with the RD bit
cleared.
The allow_snoop action gives nonrecursive access too. This give
both recursive and non recursive access. The name allow_snoop
refers to cache snooping, a technique to use nonrecursive queries
to examine the cache contents (for malicious acts). However,
nonrecursive queries can also be a valuable debugging tool (when
you want to examine the cache contents). In that case use
allow_snoop for your administration host.
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The allow_cookie action allows access only to UDP queries that
contain a valid DNS Cookie as specified in RFC 7873 and RFC 9018,
when the answer-cookie option is enabled. UDP queries containing
only a DNS Client Cookie and no Server Cookie, or an invalid DNS
Cookie, will receive a BADCOOKIE response including a newly
generated DNS Cookie, allowing clients to retry with that DNS
Cookie. The allow_cookie action will also accept requests over
stateful transports, regardless of the presence of an DNS Cookie
and regardless of the answer-cookie setting. UDP queries without
a DNS Cookie receive REFUSED responses with the TC flag set, that
may trigger fall back to TCP for those clients.
By default only localhost is allowed, the rest is refused. The
default is refused, because that is protocol-friendly. The DNS
protocol is not designed to handle dropped packets due to policy,
and dropping may result in (possibly excessive) retried queries.
The deny_non_local and refuse_non_local settings are for hosts
that are only allowed to query for the authoritative local-data,
they are not allowed full recursion but only the static data.
With deny_non_local, messages that are disallowed are dropped,
with refuse_non_local they receive error code REFUSED.
access-control-tag: <IP netblock> <"list of tags">
Assign tags to access-control elements. Clients using this access
control element use localzones that are tagged with one of these
tags. Tags must be defined in define-tags. Enclose list of tags
in quotes ("") and put spaces between tags. If access-control-tag
is configured for a netblock that does not have an
access-control, an access-control element with action allow is
configured for this netblock.
access-control-tag-action: <IP netblock> <tag> <action>
Set action for particular tag for given access control element.
If you have multiple tag values, the tag used to lookup the
action is the first tag match between access-control-tag and
local-zone-tag where "first" comes from the order of the define-
tag values.
access-control-tag-data: <IP netblock> <tag> <"resource record
Set redirect data for particular tag for given access control
element.
access-control-view: <IP netblock> <view name>
Set view for given access control element.
interface-action: <ip address or interface name
Similar to access-control: but for interfaces.
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The action is the same as the ones defined under access-control:.
Interfaces are refused by default. By default only localhost
(the IP netblock, not the loopback interface) is allowed through
the default access-control: behavior.
Note that the interface needs to be already specified with
interface: and that any access-control*: setting overrides all
interface-*: settings for targeted clients.
interface-tag: <ip address or interface name
Similar to access-control-tag: but for interfaces.
Note that the interface needs to be already specified with
interface: and that any access-control*: setting overrides all
interface-*: settings for targeted clients.
interface-tag-action: <ip address or interface name
Similar to access-control-tag-action: but for interfaces.
Note that the interface needs to be already specified with
interface: and that any access-control*: setting overrides all
interface-*: settings for targeted clients.
interface-tag-data: <ip address or interface name
Similar to access-control-tag-data: but for interfaces.
Note that the interface needs to be already specified with
interface: and that any access-control*: setting overrides all
interface-*: settings for targeted clients.
interface-view: <ip address or interface name
Similar to access-control-view: but for interfaces.
Note that the interface needs to be already specified with
interface: and that any access-control*: setting overrides all
interface-*: settings for targeted clients.
chroot: <directory>
If chroot is enabled, you should pass the configfile (from the
commandline) as a full path from the original root. After the
chroot has been performed the now defunct portion of the config
file path is removed to be able to reread the config after a
reload.
All other file paths (working dir, logfile, roothints, and key
files) can be specified in several ways: as an absolute path
relative to the new root, as a relative path to the working
directory, or as an absolute path relative to the original root.
In the last case the path is adjusted to remove the unused
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portion.
The pidfile can be either a relative path to the working
directory, or an absolute path relative to the original root. It
is written just prior to chroot and dropping permissions. This
allows the pidfile to be /var/run/unbound.pid and the chroot to
be /var/unbound, for example. Note that Unbound is not able to
remove the pidfile after termination when it is located outside
of the chroot directory.
Additionally, Unbound may need to access /dev/urandom (for
entropy) from inside the chroot.
If given a chroot is done to the given directory. By default
chroot is enabled and the default is "/usr/local/etc/unbound". If
you give "" no chroot is performed.
username: <name>
If given, after binding the port the user privileges are dropped.
Default is "unbound". If you give username: "" no user change is
performed.
If this user is not capable of binding the port, reloads (by
signal HUP) will still retain the opened ports. If you change
the port number in the config file, and that new port number
requires privileges, then a reload will fail; a restart is
needed.
directory: <directory>
Sets the working directory for the program. Default is
"/usr/local/etc/unbound". On Windows the string "%EXECUTABLE%"
tries to change to the directory that unbound.exe resides in. If
you give a server: directory: dir before include: file statements
then those includes can be relative to the working directory.
logfile: <filename>
If "" is given, logging goes to stderr, or nowhere once
daemonized. The logfile is appended to, in the following format:
[seconds since 1970] unbound[pid:tid]: type: message.
If this option is given, the use-syslog is option is set to "no".
The logfile is reopened (for append) when the config file is
reread, on SIGHUP.
use-syslog: <yes or no>
Sets Unbound to send log messages to the syslogd, using
syslog(3). The log facility LOG_DAEMON is used, with identity
"unbound". The logfile setting is overridden when use-syslog is
turned on. The default is to log to syslog.
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log-identity: <string>
If "" is given (default), then the name of the executable,
usually "unbound" is used to report to the log. Enter a string
to override it with that, which is useful on systems that run
more than one instance of Unbound, with different configurations,
so that the logs can be easily distinguished against.
log-time-ascii: <yes or no>
Sets logfile lines to use a timestamp in UTC ascii. Default is
no, which prints the seconds since 1970 in brackets. No effect if
using syslog, in that case syslog formats the timestamp printed
into the log files.
log-queries: <yes or no>
Prints one line per query to the log, with the log timestamp and
IP address, name, type and class. Default is no. Note that it
takes time to print these lines which makes the server
(significantly) slower. Odd (nonprintable) characters in names
are printed as '?'.
log-replies: <yes or no>
Prints one line per reply to the log, with the log timestamp and
IP address, name, type, class, return code, time to resolve, from
cache and response size. Default is no. Note that it takes time
to print these lines which makes the server (significantly)
slower. Odd (nonprintable) characters in names are printed as
'?'.
log-tag-queryreply: <yes or no>
Prints the word 'query' and 'reply' with log-queries and
log-replies. This makes filtering logs easier. The default is
off (for backwards compatibility).
log-destaddr: <yes or no>
Prints the destination address, port and type in the log-replies
output. This disambiguates what type of traffic, eg. udp or tcp,
and to what local port the traffic was sent to.
log-local-actions: <yes or no>
Print log lines to inform about local zone actions. These lines
are like the local-zone type inform prints out, but they are also
printed for the other types of local zones.
log-servfail: <yes or no>
Print log lines that say why queries return SERVFAIL to clients.
This is separate from the verbosity debug logs, much smaller, and
printed at the error level, not the info level of debug info from
verbosity.
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pidfile: <filename>
The process id is written to the file. Default is
"/usr/local/etc/unbound/unbound.pid". So,
kill -HUP `cat /usr/local/etc/unbound/unbound.pid`
triggers a reload,
kill -TERM `cat /usr/local/etc/unbound/unbound.pid`
gracefully terminates.
root-hints: <filename>
Read the root hints from this file. Default is nothing, using
builtin hints for the IN class. The file has the format of zone
files, with root nameserver names and addresses only. The default
may become outdated, when servers change, therefore it is good
practice to use a root-hints file.
hide-identity: <yes or no>
If enabled id.server and hostname.bind queries are refused.
identity: <string>
Set the identity to report. If set to "", the default, then the
hostname of the server is returned.
hide-version: <yes or no>
If enabled version.server and version.bind queries are refused.
version: <string>
Set the version to report. If set to "", the default, then the
package version is returned.
hide-http-user-agent: <yes or no>
If enabled the HTTP header User-Agent is not set. Use with
caution as some webserver configurations may reject HTTP requests
lacking this header. If needed, it is better to explicitly set
the http-user-agent below.
http-user-agent: <string>
Set the HTTP User-Agent header for outgoing HTTP requests. If set
to "", the default, then the package name and version are used.
nsid: <string>
Add the specified nsid to the EDNS section of the answer when
queried with an NSID EDNS enabled packet. As a sequence of hex
characters or with ascii_ prefix and then an ascii string.
hide-trustanchor: <yes or no>
If enabled trustanchor.unbound queries are refused.
target-fetch-policy: <"list of numbers">
Set the target fetch policy used by Unbound to determine if it
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Mar 14, 2024
should fetch nameserver target addresses opportunistically. The
policy is described per dependency depth.
The number of values determines the maximum dependency depth that
Unbound will pursue in answering a query. A value of -1 means to
fetch all targets opportunistically for that dependency depth. A
value of 0 means to fetch on demand only. A positive value
fetches that many targets opportunistically.
Enclose the list between quotes ("") and put spaces between
numbers. The default is "3 2 1 0 0". Setting all zeroes, "0 0 0
0 0" gives behaviour closer to that of BIND 9, while setting "-1
-1 -1 -1 -1" gives behaviour rumoured to be closer to that of
BIND 8.
harden-short-bufsize: <yes or no>
Very small EDNS buffer sizes from queries are ignored. Default is
on, as described in the standard.
harden-large-queries: <yes or no>
Very large queries are ignored. Default is off, since it is legal
protocol wise to send these, and could be necessary for operation
if TSIG or EDNS payload is very large.
harden-glue: <yes or no>
Will trust glue only if it is within the servers authority.
Default is yes.
harden-dnssec-stripped: <yes or no>
Require DNSSEC data for trust-anchored zones, if such data is
absent, the zone becomes bogus. If turned off, and no DNSSEC data
is received (or the DNSKEY data fails to validate), then the zone
is made insecure, this behaves like there is no trust anchor. You
could turn this off if you are sometimes behind an intrusive
firewall (of some sort) that removes DNSSEC data from packets, or
a zone changes from signed to unsigned to badly signed often. If
turned off you run the risk of a downgrade attack that disables
security for a zone. Default is yes.
harden-below-nxdomain: <yes or no>
From RFC 8020 (with title "NXDOMAIN: There Really Is Nothing
Underneath"), returns nxdomain to queries for a name below
another name that is already known to be nxdomain. DNSSEC
mandates noerror for empty nonterminals, hence this is possible.
Very old software might return nxdomain for empty nonterminals
(that usually happen for reverse IP address lookups), and thus
may be incompatible with this. To try to avoid this only
DNSSEC-secure nxdomains are used, because the old software does
not have DNSSEC. Default is yes. The nxdomain must be secure,
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this means nsec3 with optout is insufficient.
harden-referral-path: <yes or no>
Harden the referral path by performing additional queries for
infrastructure data. Validates the replies if trust anchors are
configured and the zones are signed. This enforces DNSSEC
validation on nameserver NS sets and the nameserver addresses
that are encountered on the referral path to the answer. Default
no, because it burdens the authority servers, and it is not RFC
standard, and could lead to performance problems because of the
extra query load that is generated. Experimental option. If you
enable it consider adding more numbers after the
target-fetch-policy to increase the max depth that is checked to.
harden-algo-downgrade: <yes or no>
Harden against algorithm downgrade when multiple algorithms are
advertised in the DS record. If no, allows the weakest algorithm
to validate the zone. Default is no. Zone signers must produce
zones that allow this feature to work, but sometimes they do not,
and turning this option off avoids that validation failure.
harden-unknown-additional: <yes or no>
Harden against unknown records in the authority section and
additional section. Default is no. If no, such records are copied
from the upstream and presented to the client together with the
answer. If yes, it could hamper future protocol developments that
want to add records.
use-caps-for-id: <yes or no>
Use 0x20-encoded random bits in the query to foil spoof attempts.
This perturbs the lowercase and uppercase of query names sent to
authority servers and checks if the reply still has the correct
casing. Disabled by default. This feature is an experimental
implementation of draft dns-0x20.
caps-exempt: <domain>
Exempt the domain so that it does not receive caps-for-id
perturbed queries. For domains that do not support 0x20 and also
fail with fallback because they keep sending different answers,
like some load balancers. Can be given multiple times, for
different domains.
caps-whitelist: <yes or no>
Alternate syntax for caps-exempt.
qname-minimisation: <yes or no>
Send minimum amount of information to upstream servers to enhance
privacy. Only send minimum required labels of the QNAME and set
QTYPE to A when possible. Best effort approach; full QNAME and
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unbound 1.19.3 unbound 1.19.3
Mar 14, 2024
original QTYPE will be sent when upstream replies with a RCODE
other than NOERROR, except when receiving NXDOMAIN from a DNSSEC
signed zone. Default is yes.
qname-minimisation-strict: <yes or no>
QNAME minimisation in strict mode. Do not fall-back to sending
full QNAME to potentially broken nameservers. A lot of domains
will not be resolvable when this option in enabled. Only use if
you know what you are doing. This option only has effect when
qname-minimisation is enabled. Default is no.
aggressive-nsec: <yes or no>
Aggressive NSEC uses the DNSSEC NSEC chain to synthesize NXDOMAIN
and other denials, using information from previous NXDOMAINs
answers. Default is yes. It helps to reduce the query rate
towards targets that get a very high nonexistent name lookup
rate.
private-address: <IP address or subnet>
Give IPv4 of IPv6 addresses or classless subnets. These are
addresses on your private network, and are not allowed to be
returned for public internet names. Any occurrence of such
addresses are removed from DNS answers. Additionally, the DNSSEC
validator may mark the answers bogus. This protects against
so-called DNS Rebinding, where a user browser is turned into a
network proxy, allowing remote access through the browser to
other parts of your private network. Some names can be allowed
to contain your private addresses, by default all the local-data
that you configured is allowed to, and you can specify additional
names using private-domain. No private addresses are enabled by
default. We consider to enable this for the RFC1918 private IP
address space by default in later releases. That would enable
private addresses for 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16
169.254.0.0/16 fd00::/8 and fe80::/10, since the RFC standards
say these addresses should not be visible on the public internet.
Turning on 127.0.0.0/8 would hinder many spamblocklists as they
use that. Adding ::ffff:0:0/96 stops IPv4-mapped IPv6 addresses
from bypassing the filter.
private-domain: <domain name>
Allow this domain, and all its subdomains to contain private
addresses. Give multiple times to allow multiple domain names to
contain private addresses. Default is none.
unwanted-reply-threshold: <number>
If set, a total number of unwanted replies is kept track of in
every thread. When it reaches the threshold, a defensive action
is taken and a warning is printed to the log. The defensive
action is to clear the rrset and message caches, hopefully
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unbound 1.19.3 unbound 1.19.3
Mar 14, 2024
flushing away any poison. A value of 10 million is suggested.
Default is 0 (turned off).
do-not-query-address: <IP address>
Do not query the given IP address. Can be IP4 or IP6. Append /num
to indicate a classless delegation netblock, for example like
10.2.3.4/24 or 2001::11/64.
do-not-query-localhost: <yes or no>
If yes, localhost is added to the do-not-query-address entries,
both IP6 ::1 and IP4 127.0.0.1/8. If no, then localhost can be
used to send queries to. Default is yes.
prefetch: <yes or no>
If yes, message cache elements are prefetched before they expire
to keep the cache up to date. Default is no. Turning it on
gives about 10 percent more traffic and load on the machine, but
popular items do not expire from the cache.
prefetch-key: <yes or no>
If yes, fetch the DNSKEYs earlier in the validation process, when
a DS record is encountered. This lowers the latency of requests.
It does use a little more CPU. Also if the cache is set to 0, it
is no use. Default is no.
deny-any: <yes or no>
If yes, deny queries of type ANY with an empty response. Default
is no. If disabled, Unbound responds with a short list of
resource records if some can be found in the cache and makes the
upstream type ANY query if there are none.
rrset-roundrobin: <yes or no>
If yes, Unbound rotates RRSet order in response (the random
number is taken from the query ID, for speed and thread safety).
Default is yes.
minimal-responses: <yes or no>
If yes, Unbound does not insert authority/additional sections
into response messages when those sections are not required.
This reduces response size significantly, and may avoid TCP
fallback for some responses. This may cause a slight speedup.
The default is yes, even though the DNS protocol RFCs mandate
these sections, and the additional content could be of use and
save roundtrips for clients. Because they are not used, and the
saved roundtrips are easier saved with prefetch, whilst this is
faster.
disable-dnssec-lame-check: <yes or no>
If true, disables the DNSSEC lameness check in the iterator.
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unbound 1.19.3 unbound 1.19.3
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This check sees if RRSIGs are present in the answer, when dnssec
is expected, and retries another authority if RRSIGs are
unexpectedly missing. The validator will insist in RRSIGs for
DNSSEC signed domains regardless of this setting, if a trust
anchor is loaded.
module-config: <"module names">
Module configuration, a list of module names separated by spaces,
surround the string with quotes (""). The modules can be respip,
validator, or iterator (and possibly more, see below). Setting
this to just "iterator" will result in a non-validating server.
Setting this to "validator iterator" will turn on DNSSEC
validation. The ordering of the modules is significant, the
order decides the order of processing. You must also set
trust-anchors for validation to be useful. Adding respip to the
front will cause RPZ processing to be done on all queries. The
default is "validator iterator".
When the server is built with EDNS client subnet support the
default is "subnetcache validator iterator". Most modules that
need to be listed here have to be listed at the beginning of the
line. The subnetcachedb module has to be listed just before the
iterator. The python module can be listed in different places,
it then processes the output of the module it is just before. The
dynlib module can be listed pretty much anywhere, it is only a
very thin wrapper that allows dynamic libraries to run in its
place.
trust-anchor-file: <filename>
File with trusted keys for validation. Both DS and DNSKEY entries
can appear in the file. The format of the file is the standard
DNS Zone file format. Default is "", or no trust anchor file.
auto-trust-anchor-file: <filename>
File with trust anchor for one zone, which is tracked with
RFC5011 probes. The probes are run several times per month, thus
the machine must be online frequently. The initial file can be
one with contents as described in trust-anchor-file. The file is
written to when the anchor is updated, so the Unbound user must
have write permission. Write permission to the file, but also to
the directory it is in (to create a temporary file, which is
necessary to deal with filesystem full events), it must also be
inside the chroot (if that is used).
trust-anchor: <"Resource Record">
A DS or DNSKEY RR for a key to use for validation. Multiple
entries can be given to specify multiple trusted keys, in
addition to the trust-anchor-files. The resource record is
entered in the same format as 'dig' or 'drill' prints them, the
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same format as in the zone file. Has to be on a single line, with
"" around it. A TTL can be specified for ease of cut and paste,
but is ignored. A class can be specified, but class IN is
default.
trusted-keys-file: <filename>
File with trusted keys for validation. Specify more than one file
with several entries, one file per entry. Like trust-anchor-file
but has a different file format. Format is BIND-9 style format,
the trusted-keys { name flag proto algo "key"; }; clauses are
read. It is possible to use wildcards with this statement, the
wildcard is expanded on start and on reload.
trust-anchor-signaling: <yes or no>
Send RFC8145 key tag query after trust anchor priming. Default is
yes.
root-key-sentinel: <yes or no>
Root key trust anchor sentinel. Default is yes.
domain-insecure: <domain name>
Sets domain name to be insecure, DNSSEC chain of trust is ignored
towards the domain name. So a trust anchor above the domain name
can not make the domain secure with a DS record, such a DS record
is then ignored. Can be given multiple times to specify multiple
domains that are treated as if unsigned. If you set trust
anchors for the domain they override this setting (and the domain
is secured).
This can be useful if you want to make sure a trust anchor for
external lookups does not affect an (unsigned) internal domain.
A DS record externally can create validation failures for that
internal domain.
val-override-date: <rrsig-style date spec>
Default is "" or "0", which disables this debugging feature. If
enabled by giving a RRSIG style date, that date is used for
verifying RRSIG inception and expiration dates, instead of the
current date. Do not set this unless you are debugging signature
inception and expiration. The value -1 ignores the date
altogether, useful for some special applications.
val-sig-skew-min: <seconds>
Minimum number of seconds of clock skew to apply to validated
signatures. A value of 10% of the signature lifetime (expiration
- inception) is used, capped by this setting. Default is 3600 (1
hour) which allows for daylight savings differences. Lower this
value for more strict checking of short lived signatures.
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val-sig-skew-max: <seconds>
Maximum number of seconds of clock skew to apply to validated
signatures. A value of 10% of the signature lifetime (expiration
- inception) is used, capped by this setting. Default is 86400
(24 hours) which allows for timezone setting problems in stable
domains. Setting both min and max very low disables the clock
skew allowances. Setting both min and max very high makes the
validator check the signature timestamps less strictly.
val-max-restart: <number>
The maximum number the validator should restart validation with
another authority in case of failed validation. Default is 5.
val-bogus-ttl: <number>
The time to live for bogus data. This is data that has failed
validation; due to invalid signatures or other checks. The TTL
from that data cannot be trusted, and this value is used instead.
The value is in seconds, default 60. The time interval prevents
repeated revalidation of bogus data.
val-clean-additional: <yes or no>
Instruct the validator to remove data from the additional section
of secure messages that are not signed properly. Messages that
are insecure, bogus, indeterminate or unchecked are not affected.
Default is yes. Use this setting to protect the users that rely
on this validator for authentication from potentially bad data in
the additional section.
val-log-level: <number>
Have the validator print validation failures to the log.
Regardless of the verbosity setting. Default is 0, off. At 1,
for every user query that fails a line is printed to the logs.
This way you can monitor what happens with validation. Use a
diagnosis tool, such as dig or drill, to find out why validation
is failing for these queries. At 2, not only the query that
failed is printed but also the reason why Unbound thought it was
wrong and which server sent the faulty data.
val-permissive-mode: <yes or no>
Instruct the validator to mark bogus messages as indeterminate.
The security checks are performed, but if the result is bogus
(failed security), the reply is not withheld from the client with
SERVFAIL as usual. The client receives the bogus data. For
messages that are found to be secure the AD bit is set in
replies. Also logging is performed as for full validation. The
default value is "no".
ignore-cd-flag: <yes or no>
Instruct Unbound to ignore the CD flag from clients and refuse to
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return bogus answers to them. Thus, the CD (Checking Disabled)
flag does not disable checking any more. This is useful if
legacy (w2008) servers that set the CD flag but cannot validate
DNSSEC themselves are the clients, and then Unbound provides them
with DNSSEC protection. The default value is "no".
disable-edns-do: <yes or no>
Disable the EDNS DO flag in upstream requests. It breaks DNSSEC
validation for Unbound's clients. This results in the upstream
name servers to not include DNSSEC records in their replies and
could be helpful for devices that cannot handle DNSSEC
information. When the option is enabled, clients that set the DO
flag receive no EDNS record in the response to indicate the lack
of support to them. If this option is enabled but Unbound is
already configured for DNSSEC validation (i.e., the validator
module is enabled; default) this option is implicitly turned off
with a warning as to not break DNSSEC validation in Unbound.
Default is no.
serve-expired: <yes or no>
If enabled, Unbound attempts to serve old responses from cache
with a TTL of serve-expired-reply-ttl in the response without
waiting for the actual resolution to finish. The actual
resolution answer ends up in the cache later on. Default is
"no".
serve-expired-ttl: <seconds>
Limit serving of expired responses to configured seconds after
expiration. 0 disables the limit. This option only applies when
serve-expired is enabled. A suggested value per RFC 8767 is
between 86400 (1 day) and 259200 (3 days). The default is 0.
serve-expired-ttl-reset: <yes or no>
Set the TTL of expired records to the serve-expired-ttl value
after a failed attempt to retrieve the record from upstream.
This makes sure that the expired records will be served as long
as there are queries for it. Default is "no".
serve-expired-reply-ttl: <seconds>
TTL value to use when replying with expired data. If
serve-expired-client-timeout is also used then it is RECOMMENDED
to use 30 as the value (RFC 8767). The default is 30.
serve-expired-client-timeout: <msec>
Time in milliseconds before replying to the client with expired
data. This essentially enables the serve-stale behavior as
specified in RFC 8767 that first tries to resolve before
immediately responding with expired data. A recommended value
per RFC 8767 is 1800. Setting this to 0 will disable this
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behavior. Default is 0.
serve-original-ttl: <yes or no>
If enabled, Unbound will always return the original TTL as
received from the upstream name server rather than the
decrementing TTL as stored in the cache. This feature may be
useful if Unbound serves as a front-end to a hidden authoritative
name server. Enabling this feature does not impact cache expiry,
it only changes the TTL Unbound embeds in responses to queries.
Note that enabling this feature implicitly disables enforcement
of the configured minimum and maximum TTL, as it is assumed users
who enable this feature do not want Unbound to change the TTL
obtained from an upstream server. Thus, the values set using
cache-min-ttl and cache-max-ttl are ignored. Default is "no".
val-nsec3-keysize-iterations: <"list of values">
List of keysize and iteration count values, separated by spaces,
surrounded by quotes. Default is "1024 150 2048 150 4096 150".
This determines the maximum allowed NSEC3 iteration count before
a message is simply marked insecure instead of performing the
many hashing iterations. The list must be in ascending order and
have at least one entry. If you set it to "1024 65535" there is
no restriction to NSEC3 iteration values. This table must be
kept short; a very long list could cause slower operation.
zonemd-permissive-mode: <yes or no>
If enabled the ZONEMD verification failures are only logged and
do not cause the zone to be blocked and only return servfail.
Useful for testing out if it works, or if the operator only wants
to be notified of a problem without disrupting service. Default
is no.
add-holddown: <seconds>
Instruct the auto-trust-anchor-file probe mechanism for RFC5011
autotrust updates to add new trust anchors only after they have
been visible for this time. Default is 30 days as per the RFC.
del-holddown: <seconds>
Instruct the auto-trust-anchor-file probe mechanism for RFC5011
autotrust updates to remove revoked trust anchors after they have
been kept in the revoked list for this long. Default is 30 days
as per the RFC.
keep-missing: <seconds>
Instruct the auto-trust-anchor-file probe mechanism for RFC5011
autotrust updates to remove missing trust anchors after they have
been unseen for this long. This cleans up the state file if the
target zone does not perform trust anchor revocation, so this
makes the auto probe mechanism work with zones that perform
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regular (non-5011) rollovers. The default is 366 days. The
value 0 does not remove missing anchors, as per the RFC.
permit-small-holddown: <yes or no>
Debug option that allows the autotrust 5011 rollover timers to
assume very small values. Default is no.
key-cache-size: <number>
Number of bytes size of the key cache. Default is 4 megabytes. A
plain number is in bytes, append 'k', 'm' or 'g' for kilobytes,
megabytes or gigabytes (1024*1024 bytes in a megabyte).
key-cache-slabs: <number>
Number of slabs in the key cache. Slabs reduce lock contention by
threads. Must be set to a power of 2. Setting (close) to the
number of cpus is a reasonable guess.
neg-cache-size: <number>
Number of bytes size of the aggressive negative cache. Default is
1 megabyte. A plain number is in bytes, append 'k', 'm' or 'g'
for kilobytes, megabytes or gigabytes (1024*1024 bytes in a
megabyte).
unblock-lan-zones: <yes or no>
Default is disabled. If enabled, then for private address space,
the reverse lookups are no longer filtered. This allows Unbound
when running as dns service on a host where it provides service
for that host, to put out all of the queries for the 'lan'
upstream. When enabled, only localhost, 127.0.0.1 reverse and
::1 reverse zones are configured with default local zones.
Disable the option when Unbound is running as a (DHCP-) DNS
network resolver for a group of machines, where such lookups
should be filtered (RFC compliance), this also stops potential
data leakage about the local network to the upstream DNS servers.
insecure-lan-zones: <yes or no>
Default is disabled. If enabled, then reverse lookups in private
address space are not validated. This is usually required
whenever unblock-lan-zones is used.
local-zone: <zone> <type>
Configure a local zone. The type determines the answer to give if
there is no match from local-data. The types are deny, refuse,
static, transparent, redirect, nodefault, typetransparent,
inform, inform_deny, inform_redirect, always_transparent,
block_a, always_refuse, always_nxdomain, always_null, noview, and
are explained below. After that the default settings are listed.
Use local-data: to enter data into the local zone. Answers for
local zones are authoritative DNS answers. By default the zones
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are class IN.
If you need more complicated authoritative data, with referrals,
wildcards, CNAME/DNAME support, or DNSSEC authoritative service,
setup a stub-zone for it as detailed in the stub zone section
below. A stub-zone can be used to have unbound send queries to
another server, an authoritative server, to fetch the
information. With a forward-zone, unbound sends queries to a
server that is a recursive server to fetch the information. With
an auth-zone a zone can be loaded from file and used, it can be
used like a local-zone for users downstream, or the auth-zone
information can be used to fetch information from when resolving
like it is an upstream server. The forward-zone and auth-zone
options are described in their sections below. If you want to
perform filtering of the information that the users can fetch,
the local-zone and local-data statements allow for this, but also
the rpz functionality can be used, described in the RPZ section.
deny Do not send an answer, drop the query. If there is a match
from local data, the query is answered.
refuse
Send an error message reply, with rcode REFUSED. If there
is a match from local data, the query is answered.
static
If there is a match from local data, the query is answered.
Otherwise, the query is answered with nodata or nxdomain.
For a negative answer a SOA is included in the answer if
present as local-data for the zone apex domain.
transparent
If there is a match from local data, the query is answered.
Otherwise if the query has a different name, the query is
resolved normally. If the query is for a name given in
localdata but no such type of data is given in localdata,
then a noerror nodata answer is returned. If no local-zone
is given local-data causes a transparent zone to be created
by default.
typetransparent
If there is a match from local data, the query is answered.
If the query is for a different name, or for the same name
but for a different type, the query is resolved normally.
So, similar to transparent but types that are not listed in
local data are resolved normally, so if an A record is in
the local data that does not cause a nodata reply for AAAA
queries.
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redirect
The query is answered from the local data for the zone name.
There may be no local data beneath the zone name. This
answers queries for the zone, and all subdomains of the zone
with the local data for the zone. It can be used to
redirect a domain to return a different address record to
the end user, with local-zone: "example.com." redirect and
local-data: "example.com. A 127.0.0.1" queries for
www.example.com and www.foo.example.com are redirected, so
that users with web browsers cannot access sites with suffix
example.com.
inform
The query is answered normally, same as transparent. The
client IP address (@portnumber) is printed to the logfile.
The log message is: timestamp, unbound-pid, info: zonename
inform IP@port queryname type class. This option can be
used for normal resolution, but machines looking up infected
names are logged, eg. to run antivirus on them.
inform_deny
The query is dropped, like 'deny', and logged, like
'inform'. Ie. find infected machines without answering the
queries.
inform_redirect
The query is redirected, like 'redirect', and logged, like
'inform'. Ie. answer queries with fixed data and also log
the machines that ask.
always_transparent
Like transparent, but ignores local data and resolves
normally.
block_a
Like transparent, but ignores local data and resolves
normally all query types excluding A. For A queries it
unconditionally returns NODATA. Useful in cases when there
is a need to explicitly force all apps to use IPv6 protocol
and avoid any queries to IPv4.
always_refuse
Like refuse, but ignores local data and refuses the query.
always_nxdomain
Like static, but ignores local data and returns nxdomain for
the query.
always_nodata
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Like static, but ignores local data and returns nodata for
the query.
always_deny
Like deny, but ignores local data and drops the query.
always_null
Always returns 0.0.0.0 or ::0 for every name in the zone.
Like redirect with zero data for A and AAAA. Ignores local
data in the zone. Used for some block lists.
noview
Breaks out of that view and moves towards the global local
zones for answer to the query. If the view first is no,
it'll resolve normally. If view first is enabled, it'll
break perform that step and check the global answers. For
when the view has view specific overrides but some zone has
to be answered from global local zone contents.
nodefault
Used to turn off default contents for AS112 zones. The other
types also turn off default contents for the zone. The
'nodefault' option has no other effect than turning off
default contents for the given zone. Use nodefault if you
use exactly that zone, if you want to use a subzone, use
transparent.
The default zones are localhost, reverse 127.0.0.1 and ::1, the
home.arpa, the onion, test, invalid and the AS112 zones. The AS112
zones are reverse DNS zones for private use and reserved IP addresses
for which the servers on the internet cannot provide correct answers.
They are configured by default to give nxdomain (no reverse
information) answers. The defaults can be turned off by specifying
your own local-zone of that name, or using the 'nodefault' type. Below
is a list of the default zone contents.
localhost
The IP4 and IP6 localhost information is given. NS and SOA
records are provided for completeness and to satisfy some
DNS update tools. Default content:
local-zone: "localhost." redirect
local-data: "localhost. 10800 IN NS localhost."
local-data: "localhost. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
local-data: "localhost. 10800 IN A 127.0.0.1"
local-data: "localhost. 10800 IN AAAA ::1"
reverse IPv4 loopback
Default content:
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local-zone: "127.in-addr.arpa." static
local-data: "127.in-addr.arpa. 10800 IN NS localhost."
local-data: "127.in-addr.arpa. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
local-data: "1.0.0.127.in-addr.arpa. 10800 IN
PTR localhost."
reverse IPv6 loopback
Default content:
local-zone: "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa." static
local-data: "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa. 10800 IN
NS localhost."
local-data: "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
local-data: "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa. 10800 IN
PTR localhost."
home.arpa (RFC 8375)
Default content:
local-zone: "home.arpa." static
local-data: "home.arpa. 10800 IN NS localhost."
local-data: "home.arpa. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
onion (RFC 7686)
Default content:
local-zone: "onion." static
local-data: "onion. 10800 IN NS localhost."
local-data: "onion. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
test (RFC 6761)
Default content:
local-zone: "test." static
local-data: "test. 10800 IN NS localhost."
local-data: "test. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
invalid (RFC 6761)
Default content:
local-zone: "invalid." static
local-data: "invalid. 10800 IN NS localhost."
local-data: "invalid. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
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reverse RFC1918 local use zones
Reverse data for zones 10.in-addr.arpa, 16.172.in-addr.arpa
to 31.172.in-addr.arpa, 168.192.in-addr.arpa. The
local-zone: is set static and as local-data: SOA and NS
records are provided.
reverse RFC3330 IP4 this, link-local, testnet and broadcast
Reverse data for zones 0.in-addr.arpa, 254.169.in-addr.arpa,
2.0.192.in-addr.arpa (TEST NET 1), 100.51.198.in-addr.arpa
(TEST NET 2), 113.0.203.in-addr.arpa (TEST NET 3),
255.255.255.255.in-addr.arpa. And from 64.100.in-addr.arpa
to 127.100.in-addr.arpa (Shared Address Space).
reverse RFC4291 IP6 unspecified
Reverse data for zone
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa.
reverse RFC4193 IPv6 Locally Assigned Local Addresses
Reverse data for zone D.F.ip6.arpa.
reverse RFC4291 IPv6 Link Local Addresses
Reverse data for zones 8.E.F.ip6.arpa to B.E.F.ip6.arpa.
reverse IPv6 Example Prefix
Reverse data for zone 8.B.D.0.1.0.0.2.ip6.arpa. This zone is
used for tutorials and examples. You can remove the block on
this zone with:
local-zone: 8.B.D.0.1.0.0.2.ip6.arpa. nodefault
You can also selectively unblock a part of the zone by
making that part transparent with a local-zone statement.
This also works with the other default zones.
local-data: "<resource record string>"
Configure local data, which is served in reply to queries for it.
The query has to match exactly unless you configure the
local-zone as redirect. If not matched exactly, the local-zone
type determines further processing. If local-data is configured
that is not a subdomain of a local-zone, a transparent local-zone
is configured. For record types such as TXT, use single quotes,
as in local-data: 'example. TXT "text"'.
If you need more complicated authoritative data, with referrals,
wildcards, CNAME/DNAME support, or DNSSEC authoritative service,
setup a stub-zone for it as detailed in the stub zone section
below.
local-data-ptr: "IPaddr name"
Configure local data shorthand for a PTR record with the reversed
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IPv4 or IPv6 address and the host name. For example "192.0.2.4
www.example.com". TTL can be inserted like this: "2001:DB8::4
7200 www.example.com"
local-zone-tag: <zone> <"list of tags">
Assign tags to localzones. Tagged localzones will only be applied
when the used access-control element has a matching tag. Tags
must be defined in define-tags. Enclose list of tags in quotes
("") and put spaces between tags. When there are multiple tags
it checks if the intersection of the list of tags for the query
and local-zone-tag is non-empty.
local-zone-override: <zone> <IP netblock> <type>
Override the localzone type for queries from addresses matching
netblock. Use this localzone type, regardless the type
configured for the local-zone (both tagged and untagged) and
regardless the type configured using access-control-tag-action.
response-ip: <IP-netblock> <action>
This requires use of the "respip" module.
If the IP address in an AAAA or A RR in the answer section of a
response matches the specified IP netblock, the specified action
will apply. <action> has generally the same semantics as that
for access-control-tag-action, but there are some exceptions.
Actions for response-ip are different from those for local-zone
in that in case of the former there is no point of such
conditions as "the query matches it but there is no local data".
Because of this difference, the semantics of response-ip actions
are modified or simplified as follows: The static, refuse,
transparent, typetransparent, and nodefault actions are invalid
for response-ip. Using any of these will cause the configuration
to be rejected as faulty. The deny action is non-conditional,
i.e. it always results in dropping the corresponding query. The
resolution result before applying the deny action is still cached
and can be used for other queries.
response-ip-data: <IP-netblock> <"resource record string">
This requires use of the "respip" module.
This specifies the action data for response-ip with action being
to redirect as specified by "resource record string". "Resource
record string" is similar to that of access-control-tag-action,
but it must be of either AAAA, A or CNAME types. If the IP-
netblock is an IPv6/IPv4 prefix, the record must be AAAA/A
respectively, unless it is a CNAME (which can be used for both
versions of IP netblocks). If it is CNAME there must not be more
than one response-ip-data for the same IP-netblock. Also, CNAME
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and other types of records must not coexist for the same IP-
netblock, following the normal rules for CNAME records. The
textual domain name for the CNAME does not have to be explicitly
terminated with a dot ("."); the root name is assumed to be the
origin for the name.
response-ip-tag: <IP-netblock> <"list of tags">
This requires use of the "respip" module.
Assign tags to response IP-netblocks. If the IP address in an
AAAA or A RR in the answer section of a response matches the
specified IP-netblock, the specified tags are assigned to the IP
address. Then, if an access-control-tag is defined for the
client and it includes one of the tags for the response IP, the
corresponding access-control-tag-action will apply. Tag matching
rule is the same as that for access-control-tag and local-zones.
Unlike local-zone-tag, response-ip-tag can be defined for an IP-
netblock even if no response-ip is defined for that netblock. If
multiple response-ip-tag options are specified for the same IP-
netblock in different statements, all but the first will be
ignored. However, this will not be flagged as a configuration
error, but the result is probably not what was intended.
Actions specified in an access-control-tag-action that has a
matching tag with response-ip-tag can be those that are "invalid"
for response-ip listed above, since access-control-tag-actions
can be shared with local zones. For these actions, if they
behave differently depending on whether local data exists or not
in case of local zones, the behavior for response-ip-data will
generally result in NOERROR/NODATA instead of NXDOMAIN, since the
response-ip data are inherently type specific, and non-existence
of data does not indicate anything about the existence or non-
existence of the qname itself. For example, if the matching tag
action is static but there is no data for the corresponding
response-ip configuration, then the result will be
NOERROR/NODATA. The only case where NXDOMAIN is returned is when
an always_nxdomain action applies.
ratelimit: <number or 0>
Enable ratelimiting of queries sent to nameserver for performing
recursion. If 0, the default, it is disabled. This option is
experimental at this time. The ratelimit is in queries per
second that are allowed. More queries are turned away with an
error (servfail). This stops recursive floods, eg. random query
names, but not spoofed reflection floods. Cached responses are
not ratelimited by this setting. The zone of the query is
determined by examining the nameservers for it, the zone name is
used to keep track of the rate. For example, 1000 may be a
suitable value to stop the server from being overloaded with
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random names, and keeps Unbound from sending traffic to the
nameservers for those zones. Configured forwarders are excluded
from ratelimiting.
ratelimit-size: <memory size>
Give the size of the data structure in which the current ongoing
rates are kept track in. Default 4m. In bytes or use m(mega),
k(kilo), g(giga). The ratelimit structure is small, so this data
structure likely does not need to be large.
ratelimit-slabs: <number>
Give power of 2 number of slabs, this is used to reduce lock
contention in the ratelimit tracking data structure. Close to
the number of cpus is a fairly good setting.
ratelimit-factor: <number>
Set the amount of queries to rate limit when the limit is
exceeded. If set to 0, all queries are dropped for domains where
the limit is exceeded. If set to another value, 1 in that number
is allowed through to complete. Default is 10, allowing 1/10
traffic to flow normally. This can make ordinary queries
complete (if repeatedly queried for), and enter the cache, whilst
also mitigating the traffic flow by the factor given.
ratelimit-backoff: <yes or no>
If enabled, the ratelimit is treated as a hard failure instead of
the default maximum allowed constant rate. When the limit is
reached, traffic is ratelimited and demand continues to be kept
track of for a 2 second rate window. No traffic is allowed,
except for ratelimit-factor, until demand decreases below the
configured ratelimit for a 2 second rate window. Useful to set
ratelimit to a suspicious rate to aggressively limit unusually
high traffic. Default is off.
ratelimit-for-domain: <domain> <number qps or 0>
Override the global ratelimit for an exact match domain name with
the listed number. You can give this for any number of names.
For example, for a top-level-domain you may want to have a higher
limit than other names. A value of 0 will disable ratelimiting
for that domain.
ratelimit-below-domain: <domain> <number qps or 0>
Override the global ratelimit for a domain name that ends in this
name. You can give this multiple times, it then describes
different settings in different parts of the namespace. The
closest matching suffix is used to determine the qps limit. The
rate for the exact matching domain name is not changed, use
ratelimit-for-domain to set that, you might want to use different
settings for a top-level-domain and subdomains. A value of 0
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will disable ratelimiting for domain names that end in this name.
ip-ratelimit: <number or 0>
Enable global ratelimiting of queries accepted per IP address.
This option is experimental at this time. The ratelimit is in
queries per second that are allowed. More queries are completely
dropped and will not receive a reply, SERVFAIL or otherwise. IP
ratelimiting happens before looking in the cache. This may be
useful for mitigating amplification attacks. Clients with a
valid DNS Cookie will bypass the ratelimit. If a ratelimit for
such clients is still needed, ip-ratelimit-cookie can be used
instead. Default is 0 (disabled).
ip-ratelimit-cookie: <number or 0>
Enable global ratelimiting of queries accepted per IP address
with a valid DNS Cookie. This option is experimental at this
time. The ratelimit is in queries per second that are allowed.
More queries are completely dropped and will not receive a reply,
SERVFAIL or otherwise. IP ratelimiting happens before looking in
the cache. This option could be useful in combination with
allow_cookie in an attempt to mitigate other amplification
attacks than UDP reflections (e.g., attacks targeting Unbound
itself) which are already handled with DNS Cookies. If used, the
value is suggested to be higher than ip-ratelimit e.g., tenfold.
Default is 0 (disabled).
ip-ratelimit-size: <memory size>
Give the size of the data structure in which the current ongoing
rates are kept track in. Default 4m. In bytes or use m(mega),
k(kilo), g(giga). The ip ratelimit structure is small, so this
data structure likely does not need to be large.
ip-ratelimit-slabs: <number>
Give power of 2 number of slabs, this is used to reduce lock
contention in the ip ratelimit tracking data structure. Close to
the number of cpus is a fairly good setting.
ip-ratelimit-factor: <number>
Set the amount of queries to rate limit when the limit is
exceeded. If set to 0, all queries are dropped for addresses
where the limit is exceeded. If set to another value, 1 in that
number is allowed through to complete. Default is 10, allowing
1/10 traffic to flow normally. This can make ordinary queries
complete (if repeatedly queried for), and enter the cache, whilst
also mitigating the traffic flow by the factor given.
ip-ratelimit-backoff: <yes or no>
If enabled, the ratelimit is treated as a hard failure instead of
the default maximum allowed constant rate. When the limit is
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reached, traffic is ratelimited and demand continues to be kept
track of for a 2 second rate window. No traffic is allowed,
except for ip-ratelimit-factor, until demand decreases below the
configured ratelimit for a 2 second rate window. Useful to set
ip-ratelimit to a suspicious rate to aggressively limit unusually
high traffic. Default is off.
outbound-msg-retry: <number>
The number of retries, per upstream nameserver in a delegation,
that Unbound will attempt in case a throwaway response is
received. No response (timeout) contributes to the retry
counter. If a forward/stub zone is used, this is the number of
retries per nameserver in the zone. Default is 5.
max-sent-count: <number>
Hard limit on the number of outgoing queries Unbound will make
while resolving a name, making sure large NS sets do not loop.
Results in SERVFAIL when reached. It resets on query restarts
(e.g., CNAME) and referrals. Default is 32.
max-query-restarts: <number>
Hard limit on the number of times Unbound is allowed to restart a
query upon encountering a CNAME record. Results in SERVFAIL when
reached. Changing this value needs caution as it can allow long
CNAME chains to be accepted, where Unbound needs to verify
(resolve) each link individually. Default is 11.
fast-server-permil: <number>
Specify how many times out of 1000 to pick from the set of
fastest servers. 0 turns the feature off. A value of 900 would
pick from the fastest servers 90 percent of the time, and would
perform normal exploration of random servers for the remaining
time. When prefetch is enabled (or serve-expired), such
prefetches are not sped up, because there is no one waiting for
it, and it presents a good moment to perform server exploration.
The fast-server-num option can be used to specify the size of the
fastest servers set. The default for fast-server-permil is 0.
fast-server-num: <number>
Set the number of servers that should be used for fast server
selection. Only use the fastest specified number of servers with
the fast-server-permil option, that turns this on or off. The
default is to use the fastest 3 servers.
answer-cookie: <yes or no>
If enabled, Unbound will answer to requests containing DNS
Cookies as specified in RFC 7873 and RFC 9018. Default is no.
cookie-secret: <128 bit hex string>
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Server's secret for DNS Cookie generation. Useful to explicitly
set for servers in an anycast deployment that need to share the
secret in order to verify each other's Server Cookies. An
example hex string would be "000102030405060708090a0b0c0d0e0f".
Default is a 128 bits random secret generated at startup time.
edns-client-string: <IP netblock> <string>
Include an EDNS0 option containing configured ascii string in
queries with destination address matching the configured IP
netblock. This configuration option can be used multiple times.
The most specific match will be used.
edns-client-string-opcode: <opcode>
EDNS0 option code for the edns-client-string option, from 0 to
65535. A value from the `Reserved for Local/Experimental` range
(65001-65534) should be used. Default is 65001.
ede: <yes or no>
If enabled, Unbound will respond with Extended DNS Error codes
(RFC8914). These EDEs attach informative error messages to a
response for various errors. Default is "no".
When the val-log-level option is also set to 2, responses with
Extended DNS Errors concerning DNSSEC failures that are not
served from cache, will also contain a descriptive text message
about the reason for the failure.
ede-serve-expired: <yes or no>
If enabled, Unbound will attach an Extended DNS Error (RFC8914)
Code 3 - Stale Answer as EDNS0 option to the expired response.
Note that this will not attach the EDE code without setting the
global ede option to "yes" as well. Default is "no".
Remote Control Options
In the remote-control: clause are the declarations for the remote
control facility. If this is enabled, the unbound-control(8) utility
can be used to send commands to the running Unbound server. The
server uses these clauses to setup TLSv1 security for the connection.
The unbound-control(8) utility also reads the remote-control section
for options. To setup the correct self-signed certificates use the
unbound-control-setup(8) utility.
control-enable: <yes or no>
The option is used to enable remote control, default is "no". If
turned off, the server does not listen for control commands.
control-interface: <ip address or interface name
Give IPv4 or IPv6 addresses or local socket path to listen on for
control commands. If an interface name is used instead of an ip
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address, the list of ip addresses on that interface are used. By
default localhost (127.0.0.1 and ::1) is listened to. Use
0.0.0.0 and ::0 to listen to all interfaces. If you change this
and permissions have been dropped, you must restart the server
for the change to take effect.
If you set it to an absolute path, a unix domain socket is used.
This socket does not use the certificates and keys, so those
files need not be present. To restrict access, Unbound sets
permissions on the file to the user and group that is configured,
the access bits are set to allow the group members to access the
control socket file. Put users that need to access the socket in
the that group. To restrict access further, create a directory
to put the control socket in and restrict access to that
directory.
control-port: <port number>
The port number to listen on for IPv4 or IPv6 control interfaces,
default is 8953. If you change this and permissions have been
dropped, you must restart the server for the change to take
effect.
control-use-cert: <yes or no>
For localhost control-interface you can disable the use of TLS by
setting this option to "no", default is "yes". For local
sockets, TLS is disabled and the value of this option is ignored.
server-key-file: <private key file>
Path to the server private key, by default unbound_server.key.
This file is generated by the unbound-control-setup utility.
This file is used by the Unbound server, but not by
unbound-control.
server-cert-file: <certificate file.pem>
Path to the server self signed certificate, by default
unbound_server.pem. This file is generated by the
unbound-control-setup utility. This file is used by the Unbound
server, and also by unbound-control.
control-key-file: <private key file>
Path to the control client private key, by default
unbound_control.key. This file is generated by the
unbound-control-setup utility. This file is used by
unbound-control.
control-cert-file: <certificate file.pem>
Path to the control client certificate, by default
unbound_control.pem. This certificate has to be signed with the
server certificate. This file is generated by the
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unbound-control-setup utility. This file is used by
unbound-control.
Stub Zone Options
There may be multiple stub-zone: clauses. Each with a name: and zero
or more hostnames or IP addresses. For the stub zone this list of
nameservers is used. Class IN is assumed. The servers should be
authority servers, not recursors; Unbound performs the recursive
processing itself for stub zones.
The stub zone can be used to configure authoritative data to be used
by the resolver that cannot be accessed using the public internet
servers. This is useful for company-local data or private zones.
Setup an authoritative server on a different host (or different port).
Enter a config entry for Unbound with stub-addr: <ip address of
host[@port]>. The Unbound resolver can then access the data, without
referring to the public internet for it.
This setup allows DNSSEC signed zones to be served by that
authoritative server, in which case a trusted key entry with the
public key can be put in config, so that Unbound can validate the data
and set the AD bit on replies for the private zone (authoritative
servers do not set the AD bit). This setup makes Unbound capable of
answering queries for the private zone, and can even set the AD bit
('authentic'), but the AA ('authoritative') bit is not set on these
replies.
Consider adding server: statements for domain-insecure: and for
local-zone: name nodefault for the zone if it is a locally served
zone. The insecure clause stops DNSSEC from invalidating the zone.
The local zone nodefault (or transparent) clause makes the (reverse-)
zone bypass Unbound's filtering of RFC1918 zones.
name: <domain name>
Name of the stub zone. This is the full domain name of the zone.
stub-host: <domain name>
Name of stub zone nameserver. Is itself resolved before it is
used. To use a nondefault port for DNS communication append '@'
with the port number. If tls is enabled, then you can append a
'#' and a name, then it'll check the tls authentication
certificates with that name. If you combine the '@' and '#', the
'@' comes first. If only '#' is used the default port is the
configured tls-port.
stub-addr: <IP address>
IP address of stub zone nameserver. Can be IP 4 or IP 6. To use
a nondefault port for DNS communication append '@' with the port
number. If tls is enabled, then you can append a '#' and a name,
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then it'll check the tls authentication certificates with that
name. If you combine the '@' and '#', the '@' comes first. If
only '#' is used the default port is the configured tls-port.
stub-prime: <yes or no>
This option is by default no. If enabled it performs NS set
priming, which is similar to root hints, where it starts using
the list of nameservers currently published by the zone. Thus,
if the hint list is slightly outdated, the resolver picks up a
correct list online.
stub-first: <yes or no>
If enabled, a query is attempted without the stub clause if it
fails. The data could not be retrieved and would have caused
SERVFAIL because the servers are unreachable, instead it is tried
without this clause. The default is no.
stub-tls-upstream: <yes or no>
Enabled or disable whether the queries to this stub use TLS for
transport. Default is no.
stub-ssl-upstream: <yes or no>
Alternate syntax for stub-tls-upstream.
stub-tcp-upstream: <yes or no>
If it is set to "yes" then upstream queries use TCP only for
transport regardless of global flag tcp-upstream. Default is no.
stub-no-cache: <yes or no>
Default is no. If enabled, data inside the stub is not cached.
This is useful when you want immediate changes to be visible.
Forward Zone Options
There may be multiple forward-zone: clauses. Each with a name: and
zero or more hostnames or IP addresses. For the forward zone this
list of nameservers is used to forward the queries to. The servers
listed as forward-host: and forward-addr: have to handle further
recursion for the query. Thus, those servers are not authority
servers, but are (just like Unbound is) recursive servers too; Unbound
does not perform recursion itself for the forward zone, it lets the
remote server do it. Class IN is assumed. CNAMEs are chased by
Unbound itself, asking the remote server for every name in the
indirection chain, to protect the local cache from illegal indirect
referenced items. A forward-zone entry with name "." and a
forward-addr target will forward all queries to that other server
(unless it can answer from the cache).
name: <domain name>
Name of the forward zone. This is the full domain name of the
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zone.
forward-host: <domain name>
Name of server to forward to. Is itself resolved before it is
used. To use a nondefault port for DNS communication append '@'
with the port number. If tls is enabled, then you can append a
'#' and a name, then it'll check the tls authentication
certificates with that name. If you combine the '@' and '#', the
'@' comes first. If only '#' is used the default port is the
configured tls-port.
forward-addr: <IP address>
IP address of server to forward to. Can be IP 4 or IP 6. To use
a nondefault port for DNS communication append '@' with the port
number. If tls is enabled, then you can append a '#' and a name,
then it'll check the tls authentication certificates with that
name. If you combine the '@' and '#', the '@' comes first. If
only '#' is used the default port is the configured tls-port.
At high verbosity it logs the TLS certificate, with TLS enabled.
If you leave out the '#' and auth name from the forward-addr, any
name is accepted. The cert must also match a CA from the
tls-cert-bundle.
forward-first: <yes or no>
If a forwarded query is met with a SERVFAIL error, and this
option is enabled, Unbound will fall back to normal recursive
resolution for this query as if no query forwarding had been
specified. The default is "no".
forward-tls-upstream: <yes or no>
Enabled or disable whether the queries to this forwarder use TLS
for transport. Default is no. If you enable this, also
configure a tls-cert-bundle or use tls-win-cert to load CA certs,
otherwise the connections cannot be authenticated.
forward-ssl-upstream: <yes or no>
Alternate syntax for forward-tls-upstream.
forward-tcp-upstream: <yes or no>
If it is set to "yes" then upstream queries use TCP only for
transport regardless of global flag tcp-upstream. Default is no.
forward-no-cache: <yes or no>
Default is no. If enabled, data inside the forward is not
cached. This is useful when you want immediate changes to be
visible.
Authority Zone Options
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Authority zones are configured with auth-zone:, and each one must have
a name:. There can be multiple ones, by listing multiple auth-zone
clauses, each with a different name, pertaining to that part of the
namespace. The authority zone with the name closest to the name
looked up is used. Authority zones can be processed on two distinct,
non-exclusive, configurable stages. With for-downstream: yes
(default), authority zones are processed after local-zones and before
cache. When used in this manner, Unbound responds like an authority
server with no further processing other than returning an answer from
the zone contents. A notable example, in this case, is CNAME records
which are returned verbatim to downstream clients without further
resolution. With for-upstream: yes (default), authority zones are
processed after the cache lookup, just before going to the network to
fetch information for recursion. When used in this manner they
provide a local copy of an authority server that speeds up lookups for
that data during resolving. If both options are enabled (default),
client queries for an authority zone are answered authoritatively from
Unbound, while internal queries that require data from the authority
zone consult the local zone data instead of going to the network. An
interesting configuration is for-downstream: no, for-upstream: yes
that allows for hyperlocal behavior where both client and internal
queries consult the local zone data while resolving. In this case,
the aforementioned CNAME example will result in a thoroughly resolved
answer. Authority zones can be read from zonefile. And can be kept
updated via AXFR and IXFR. After update the zonefile is rewritten.
The update mechanism uses the SOA timer values and performs SOA UDP
queries to detect zone changes. If the update fetch fails, the timers
in the SOA record are used to time another fetch attempt. Until the
SOA expiry timer is reached. Then the zone is expired. When a zone
is expired, queries are SERVFAIL, and any new serial number is
accepted from the primary (even if older), and if fallback is enabled,
the fallback activates to fetch from the upstream instead of the
SERVFAIL.
name: <zone name>
Name of the authority zone.
primary: <IP address or host name>
Where to download a copy of the zone from, with AXFR and IXFR.
Multiple primaries can be specified. They are all tried if one
fails. To use a nondefault port for DNS communication append '@'
with the port number. You can append a '#' and a name, then AXFR
over TLS can be used and the tls authentication certificates will
be checked with that name. If you combine the '@' and '#', the
'@' comes first. If you point it at another Unbound instance, it
would not work because that does not support AXFR/IXFR for the
zone, but if you used url: to download the zonefile as a text
file from a webserver that would work. If you specify the
hostname, you cannot use the domain from the zonefile, because it
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may not have that when retrieving that data, instead use a plain
IP address to avoid a circular dependency on retrieving that IP
address.
master: <IP address or host name>
Alternate syntax for primary.
url: <url to zonefile>
Where to download a zonefile for the zone. With http or https.
An example for the url is
"http://www.example.com/example.org.zone". Multiple url
statements can be given, they are tried in turn. If only urls
are given the SOA refresh timer is used to wait for making new
downloads. If also primaries are listed, the primaries are first
probed with UDP SOA queries to see if the SOA serial number has
changed, reducing the number of downloads. If none of the urls
work, the primaries are tried with IXFR and AXFR. For https, the
tls-cert-bundle and the hostname from the url are used to
authenticate the connection. If you specify a hostname in the
URL, you cannot use the domain from the zonefile, because it may
not have that when retrieving that data, instead use a plain IP
address to avoid a circular dependency on retrieving that IP
address. Avoid dependencies on name lookups by using a notation
like "http://192.0.2.1/unbound-primaries/example.com.zone", with
an explicit IP address.
allow-notify: <IP address or host name
With allow-notify you can specify additional sources of notifies.
When notified, the server attempts to first probe and then zone
transfer. If the notify is from a primary, it first attempts
that primary. Otherwise other primaries are attempted. If there
are no primaries, but only urls, the file is downloaded when
notified. The primaries from primary: and url: statements are
allowed notify by default.
fallback-enabled: <yes or no>
Default no. If enabled, Unbound falls back to querying the
internet as a resolver for this zone when lookups fail. For
example for DNSSEC validation failures.
for-downstream: <yes or no>
Default yes. If enabled, Unbound serves authority responses to
downstream clients for this zone. This option makes Unbound
behave, for the queries with names in this zone, like one of the
authority servers for that zone. Turn it off if you want Unbound
to provide recursion for the zone but have a local copy of zone
data. If for-downstream is no and for-upstream is yes, then
Unbound will DNSSEC validate the contents of the zone before
serving the zone contents to clients and store validation results
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in the cache.
for-upstream: <yes or no>
Default yes. If enabled, Unbound fetches data from this data
collection for answering recursion queries. Instead of sending
queries over the internet to the authority servers for this zone,
it'll fetch the data directly from the zone data. Turn it on
when you want Unbound to provide recursion for downstream
clients, and use the zone data as a local copy to speed up
lookups.
zonemd-check: <yes or no>
Enable this option to check ZONEMD records in the zone. Default
is disabled. The ZONEMD record is a checksum over the zone data.
This includes glue in the zone and data from the zone file, and
excludes comments from the zone file. When there is a DNSSEC
chain of trust, DNSSEC signatures are checked too.
zonemd-reject-absence: <yes or no>
Enable this option to reject the absence of the ZONEMD record.
Without it, when zonemd is not there it is not checked. It is
useful to enable for a nonDNSSEC signed zone where the operator
wants to require the verification of a ZONEMD, hence a missing
ZONEMD is a failure. The action upon failure is controlled by
the zonemd-permissive-mode option, for log only or also block the
zone. The default is no.
Without the option absence of a ZONEMD is only a failure when the
zone is DNSSEC signed, and we have a trust anchor, and the DNSSEC
verification of the absence of the ZONEMD fails. With the option
enabled, the absence of a ZONEMD is always a failure, also for
nonDNSSEC signed zones.
zonefile: <filename>
The filename where the zone is stored. If not given then no
zonefile is used. If the file does not exist or is empty,
Unbound will attempt to fetch zone data (eg. from the primary
servers).
View Options
There may be multiple view: clauses. Each with a name: and zero or
more local-zone and local-data elements. Views can also contain
view-first, response-ip, response-ip-data and local-data-ptr elements.
View can be mapped to requests by specifying the view name in an
access-control-view element. Options from matching views will override
global options. Global options will be used if no matching view is
found, or when the matching view does not have the option specified.
name: <view name>
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Name of the view. Must be unique. This name is used in
access-control-view elements.
local-zone: <zone> <type>
View specific local-zone elements. Has the same types and
behaviour as the global local-zone elements. When there is at
least one local-zone specified and view-first is no, the default
local-zones will be added to this view. Defaults can be disabled
using the nodefault type. When view-first is yes or when a view
does not have a local-zone, the global local-zone will be used
including it's default zones.
local-data: "<resource record string>"
View specific local-data elements. Has the same behaviour as the
global local-data elements.
local-data-ptr: "IPaddr name"
View specific local-data-ptr elements. Has the same behaviour as
the global local-data-ptr elements.
view-first: <yes or no>
If enabled, it attempts to use the global local-zone and
local-data if there is no match in the view specific options.
The default is no.
Python Module Options
The python: clause gives the settings for the python(1) script module.
This module acts like the iterator and validator modules do, on
queries and answers. To enable the script module it has to be
compiled into the daemon, and the word "python" has to be put in the
module-config: option (usually first, or between the validator and
iterator). Multiple instances of the python module are supported by
adding the word "python" more than once. If the chroot: option is
enabled, you should make sure Python's library directory structure is
bind mounted in the new root environment, see mount(8). Also the
python-script: path should be specified as an absolute path relative
to the new root, or as a relative path to the working directory.
python-script: <python file>
The script file to load. Repeat this option for every python
module instance added to the module-config: option.
Dynamic Library Module Options
The dynlib: clause gives the settings for the dynlib module. This
module is only a very small wrapper that allows dynamic modules to be
loaded on runtime instead of being compiled into the application. To
enable the dynlib module it has to be compiled into the daemon, and
the word "dynlib" has to be put in the module-config: option. Multiple
instances of dynamic libraries are supported by adding the word
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"dynlib" more than once. The dynlib-file: path should be specified as
an absolute path relative to the new path set by chroot: option, or as
a relative path to the working directory.
dynlib-file: <dynlib file>
The dynamic library file to load. Repeat this option for every
dynlib module instance added to the module-config: option.
DNS64 Module Options
The dns64 module must be configured in the module-config: "dns64
validator iterator" directive and be compiled into the daemon to be
enabled. These settings go in the server: section.
dns64-prefix: <IPv6 prefix>
This sets the DNS64 prefix to use to synthesize AAAA records
with. It must be /96 or shorter. The default prefix is
64:ff9b::/96.
dns64-synthall: <yes or no>
Debug option, default no. If enabled, synthesize all AAAA
records despite the presence of actual AAAA records.
dns64-ignore-aaaa: <name>
List domain for which the AAAA records are ignored and the A
record is used by dns64 processing instead. Can be entered
multiple times, list a new domain for which it applies, one per
line. Applies also to names underneath the name given.
NAT64 Operation
NAT64 operation allows using a NAT64 prefix for outbound requests to
IPv4-only servers. It is controlled by two options in the server:
section:
do-nat64: <yes or no>
Use NAT64 to reach IPv4-only servers. Consider also enabling
prefer-ip6 to prefer native IPv6 connections to nameservers.
Default no.
nat64-prefix: <IPv6 prefix>
Use a specific NAT64 prefix to reach IPv4-only servers. Defaults
to using the prefix configured in dns64-prefix, which in turn
defaults to 64:ff9b::/96. The prefix length must be one of /32,
/40, /48, /56, /64 or /96.
DNSCrypt Options
The dnscrypt: clause gives the settings of the dnscrypt channel. While
those options are available, they are only meaningful if Unbound was
compiled with --enable-dnscrypt. Currently certificate and
secret/public keys cannot be generated by Unbound. You can use
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dnscrypt-wrapper to generate those:
https://github.com/cofyc/dnscrypt-wrapper/blob/master/README.md#usage
dnscrypt-enable: <yes or no>
Whether or not the dnscrypt config should be enabled. You may
define configuration but not activate it. The default is no.
dnscrypt-port: <port number>
On which port should dnscrypt should be activated. Note that you
should have a matching interface option defined in the server
section for this port.
dnscrypt-provider: <provider name>
The provider name to use to distribute certificates. This is of
the form: 2.dnscrypt-cert.example.com.. The name MUST end with a
dot.
dnscrypt-secret-key: <path to secret key file>
Path to the time limited secret key file. This option may be
specified multiple times.
dnscrypt-provider-cert: <path to cert file>
Path to the certificate related to the dnscrypt-secret-keys.
This option may be specified multiple times.
dnscrypt-provider-cert-rotated: <path to cert file>
Path to a certificate that we should be able to serve existing
connection from but do not want to advertise over
dnscrypt-provider's TXT record certs distribution. A typical use
case is when rotating certificates, existing clients may still
use the client magic from the old cert in their queries until
they fetch and update the new cert. Likewise, it would allow one
to prime the new cert/key without distributing the new cert yet,
this can be useful when using a network of servers using anycast
and on which the configuration may not get updated at the exact
same time. By priming the cert, the servers can handle both old
and new certs traffic while distributing only one. This option
may be specified multiple times.
dnscrypt-shared-secret-cache-size: <memory size>
Give the size of the data structure in which the shared secret
keys are kept in. Default 4m. In bytes or use m(mega), k(kilo),
g(giga). The shared secret cache is used when a same client is
making multiple queries using the same public key. It saves a
substantial amount of CPU.
dnscrypt-shared-secret-cache-slabs: <number>
Give power of 2 number of slabs, this is used to reduce lock
contention in the dnscrypt shared secrets cache. Close to the
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number of cpus is a fairly good setting.
dnscrypt-nonce-cache-size: <memory size>
Give the size of the data structure in which the client nonces
are kept in. Default 4m. In bytes or use m(mega), k(kilo),
g(giga). The nonce cache is used to prevent dnscrypt message
replaying. Client nonce should be unique for any pair of client
pk/server sk.
dnscrypt-nonce-cache-slabs: <number>
Give power of 2 number of slabs, this is used to reduce lock
contention in the dnscrypt nonce cache. Close to the number of
cpus is a fairly good setting.
EDNS Client Subnet Module Options
The ECS module must be configured in the module-config: "subnetcache
validator iterator" directive and be compiled into the daemon to be
enabled. These settings go in the server: section. If the
destination address is allowed in the configuration Unbound will add
the EDNS0 option to the query containing the relevant part of the
client's address. When an answer contains the ECS option the response
and the option are placed in a specialized cache. If the authority
indicated no support, the response is stored in the regular cache.
Additionally, when a client includes the option in its queries,
Unbound will forward the option when sending the query to addresses
that are explicitly allowed in the configuration using
send-client-subnet. The option will always be forwarded, regardless
the allowed addresses, if client-subnet-always-forward is set to yes.
In this case the lookup in the regular cache is skipped. The maximum
size of the ECS cache is controlled by 'msg-cache-size' in the
configuration file. On top of that, for each query only 100 different
subnets are allowed to be stored for each address family. Exceeding
that number, older entries will be purged from cache. This module
does not interact with the serve-expired* and prefetch: options.
send-client-subnet: <IP address>
Send client source address to this authority. Append /num to
indicate a classless delegation netblock, for example like
10.2.3.4/24 or 2001::11/64. Can be given multiple times.
Authorities not listed will not receive edns-subnet information,
unless domain in query is specified in client-subnet-zone.
client-subnet-zone: <domain>
Send client source address in queries for this domain and its
subdomains. Can be given multiple times. Zones not listed will
not receive edns-subnet information, unless hosted by authority
specified in send-client-subnet.
client-subnet-always-forward: <yes or no>
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Specify whether the ECS address check (configured using
send-client-subnet) is applied for all queries, even if the
triggering query contains an ECS record, or only for queries for
which the ECS record is generated using the querier address (and
therefore did not contain ECS data in the client query). If
enabled, the address check is skipped when the client query
contains an ECS record. And the lookup in the regular cache is
skipped. Default is no.
max-client-subnet-ipv6: <number>
Specifies the maximum prefix length of the client source address
we are willing to expose to third parties for IPv6. Defaults to
56.
max-client-subnet-ipv4: <number>
Specifies the maximum prefix length of the client source address
we are willing to expose to third parties for IPv4. Defaults to
24.
min-client-subnet-ipv6: <number>
Specifies the minimum prefix length of the IPv6 source mask we
are willing to accept in queries. Shorter source masks result in
REFUSED answers. Source mask of 0 is always accepted. Default is
0.
min-client-subnet-ipv4: <number>
Specifies the minimum prefix length of the IPv4 source mask we
are willing to accept in queries. Shorter source masks result in
REFUSED answers. Source mask of 0 is always accepted. Default is
0.
max-ecs-tree-size-ipv4: <number>
Specifies the maximum number of subnets ECS answers kept in the
ECS radix tree. This number applies for each qname/qclass/qtype
tuple. Defaults to 100.
max-ecs-tree-size-ipv6: <number>
Specifies the maximum number of subnets ECS answers kept in the
ECS radix tree. This number applies for each qname/qclass/qtype
tuple. Defaults to 100.
Opportunistic IPsec Support Module Options
The IPsec module must be configured in the module-config: "ipsecmod
validator iterator" directive and be compiled into Unbound by using
--enable-ipsecmod to be enabled. These settings go in the server:
section. When Unbound receives an A/AAAA query that is not in the
cache and finds a valid answer, it will withhold returning the answer
and instead will generate an IPSECKEY subquery for the same domain
name. If an answer was found, Unbound will call an external hook
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passing the following arguments:
QNAME
Domain name of the A/AAAA and IPSECKEY query. In string
format.
IPSECKEY TTL
TTL of the IPSECKEY RRset.
A/AAAA
String of space separated IP addresses present in the A/AAAA
RRset. The IP addresses are in string format.
IPSECKEY
String of space separated IPSECKEY RDATA present in the
IPSECKEY RRset. The IPSECKEY RDATA are in DNS presentation
format. The A/AAAA answer is then cached and returned to
the client. If the external hook was called the TTL changes
to ensure it doesn't surpass ipsecmod-max-ttl. The same
procedure is also followed when prefetch: is used, but the
A/AAAA answer is given to the client before the hook is
called. ipsecmod-max-ttl ensures that the A/AAAA answer
given from cache is still relevant for opportunistic IPsec.
ipsecmod-enabled: <yes or no>
Specifies whether the IPsec module is enabled or not. The
IPsec module still needs to be defined in the module-config:
directive. This option facilitates turning on/off the
module without restarting/reloading Unbound. Defaults to
yes.
ipsecmod-hook: <filename>
Specifies the external hook that Unbound will call with
system(3). The file can be specified as an
absolute/relative path. The file needs the proper
permissions to be able to be executed by the same user that
runs Unbound. It must be present when the IPsec module is
defined in the module-config: directive.
ipsecmod-strict: <yes or no>
If enabled Unbound requires the external hook to return a
success value of 0. Failing to do so Unbound will reply
with SERVFAIL. The A/AAAA answer will also not be cached.
Defaults to no.
ipsecmod-max-ttl: <seconds>
Time to live maximum for A/AAAA cached records after calling
the external hook. Defaults to 3600.
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ipsecmod-ignore-bogus: <yes or no>
Specifies the behaviour of Unbound when the IPSECKEY answer
is bogus. If set to yes, the hook will be called and the
A/AAAA answer will be returned to the client. If set to no,
the hook will not be called and the answer to the A/AAAA
query will be SERVFAIL. Mainly used for testing. Defaults
to no.
ipsecmod-allow: <domain>
Allow the ipsecmod functionality for the domain so that the
module logic will be executed. Can be given multiple times,
for different domains. If the option is not specified, all
domains are treated as being allowed (default).
ipsecmod-whitelist: <yes or no>
Alternate syntax for ipsecmod-allow.
Cache DB Module Options
The Cache DB module must be configured in the module-config:
"validator cachedb iterator" directive and be compiled into the daemon
with --enable-cachedb. If this module is enabled and configured, the
specified backend database works as a second level cache: When Unbound
cannot find an answer to a query in its built-in in-memory cache, it
consults the specified backend. If it finds a valid answer in the
backend, Unbound uses it to respond to the query without performing
iterative DNS resolution. If Unbound cannot even find an answer in
the backend, it resolves the query as usual, and stores the answer in
the backend.
This module interacts with the serve-expired-* options and will reply
with expired data if Unbound is configured for that. Currently the
use of serve-expired-client-timeout: and serve-expired-reply-ttl: is
not consistent for data originating from the external cache as these
will result in a reply with 0 TTL without trying to update the data
first, ignoring the configured values.
If Unbound was built with --with-libhiredis on a system that has
installed the hiredis C client library of Redis, then the "redis"
backend can be used. This backend communicates with the specified
Redis server over a TCP connection to store and retrieve cache data.
It can be used as a persistent and/or shared cache backend. It should
be noted that Unbound never removes data stored in the Redis server,
even if some data have expired in terms of DNS TTL or the Redis server
has cached too much data; if necessary the Redis server must be
configured to limit the cache size, preferably with some kind of
least-recently-used eviction policy. Additionally, the
redis-expire-records option can be used in order to set the relative
DNS TTL of the message as timeout to the Redis records; keep in mind
that some additional memory is used per key and that the expire
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information is stored as absolute Unix timestamps in Redis (computer
time must be stable). This backend uses synchronous communication
with the Redis server based on the assumption that the communication
is stable and sufficiently fast. The thread waiting for a response
from the Redis server cannot handle other DNS queries. Although the
backend has the ability to reconnect to the server when the connection
is closed unexpectedly and there is a configurable timeout in case the
server is overly slow or hangs up, these cases are assumed to be very
rare. If connection close or timeout happens too often, Unbound will
be effectively unusable with this backend. It's the administrator's
responsibility to make the assumption hold.
The cachedb: clause gives custom settings of the cache DB module.
backend: <backend name>
Specify the backend database name. The default database is the
in-memory backend named "testframe", which, as the name suggests,
is not of any practical use. Depending on the build-time
configuration, "redis" backend may also be used as described
above.
secret-seed: <"secret string">
Specify a seed to calculate a hash value from query information.
This value will be used as the key of the corresponding answer
for the backend database and can be customized if the hash should
not be predictable operationally. If the backend database is
shared by multiple Unbound instances, all instances must use the
same secret seed. This option defaults to "default".
cachedb-no-store: <yes or no>
If the backend should be read from, but not written to. This
makes this instance not store dns messages in the backend. But if
data is available it is retrieved. The default is no.
The following cachedb options are specific to the redis backend.
redis-server-host: <server address or name>
The IP (either v6 or v4) address or domain name of the Redis
server. In general an IP address should be specified as
otherwise Unbound will have to resolve the name of the server
every time it establishes a connection to the server. This
option defaults to "127.0.0.1".
redis-server-port: <port number>
The TCP port number of the Redis server. This option defaults to
6379.
redis-server-path: <unix socket path>
The unix socket path to connect to the redis server. Off by
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default, and it can be set to "" to turn this off. Unix sockets
may have better throughput than the IP address option.
redis-server-password: "<password>"
The Redis AUTH password to use for the redis server. Only
relevant if Redis is configured for client password
authorisation. Off by default, and it can be set to "" to turn
this off.
redis-timeout: <msec>
The period until when Unbound waits for a response from the Redis
sever. If this timeout expires Unbound closes the connection,
treats it as if the Redis server does not have the requested
data, and will try to re-establish a new connection later. This
option defaults to 100 milliseconds.
redis-expire-records: <yes or no>
If Redis record expiration is enabled. If yes, Unbound sets
timeout for Redis records so that Redis can evict keys that have
expired automatically. If Unbound is configured with serve-
expired and serve-expired-ttl is 0, this option is internally
reverted to "no". Redis SETEX support is required for this
option (Redis >= 2.0.0). This option defaults to no.
redis-logical-db: <logical database index>
The logical database in Redis to use. These are databases in the
same Redis instance sharing the same configuration and persisted
in the same RDB/AOF file. If unsure about using this option,
Redis documentation (https://redis.io/commands/select/) suggests
not to use a single Redis instance for multiple unrelated
applications. The default database in Redis is 0 while other
logical databases need to be explicitly SELECT'ed upon
connecting. This option defaults to 0.
DNSTAP Logging Options
DNSTAP support, when compiled in by using --enable-dnstap, is enabled
in the dnstap: section. This starts an extra thread (when compiled
with threading) that writes the log information to the destination.
If Unbound is compiled without threading it does not spawn a thread,
but connects per-process to the destination.
dnstap-enable: <yes or no>
If dnstap is enabled. Default no. If yes, it connects to the
dnstap server and if any of the dnstap-log-..-messages options is
enabled it sends logs for those messages to the server.
dnstap-bidirectional: <yes or no>
Use frame streams in bidirectional mode to transfer DNSTAP
messages. Default is yes.
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dnstap-socket-path: <file name>
Sets the unix socket file name for connecting to the server that
is listening on that socket. Default is "".
dnstap-ip: <IPaddress[@port]>
If "", the unix socket is used, if set with an IP address (IPv4
or IPv6) that address is used to connect to the server.
dnstap-tls: <yes or no>
Set this to use TLS to connect to the server specified in
dnstap-ip. The default is yes. If set to no, TCP is used to
connect to the server.
dnstap-tls-server-name: <name of TLS authentication>
The TLS server name to authenticate the server with. Used when
dnstap-tls is enabled. If "" it is ignored, default "".
dnstap-tls-cert-bundle: <file name of cert bundle>
The pem file with certs to verify the TLS server certificate. If
"" the server default cert bundle is used, or the windows cert
bundle on windows. Default is "".
dnstap-tls-client-key-file: <file name>
The client key file for TLS client authentication. If "" client
authentication is not used. Default is "".
dnstap-tls-client-cert-file: <file name>
The client cert file for TLS client authentication. Default is
"".
dnstap-send-identity: <yes or no>
If enabled, the server identity is included in the log messages.
Default is no.
dnstap-send-version: <yes or no>
If enabled, the server version if included in the log messages.
Default is no.
dnstap-identity: <string>
The identity to send with messages, if "" the hostname is used.
Default is "".
dnstap-version: <string>
The version to send with messages, if "" the package version is
used. Default is "".
dnstap-log-resolver-query-messages: <yes or no>
Enable to log resolver query messages. Default is no. These are
messages from Unbound to upstream servers.
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dnstap-log-resolver-response-messages: <yes or no>
Enable to log resolver response messages. Default is no. These
are replies from upstream servers to Unbound.
dnstap-log-client-query-messages: <yes or no>
Enable to log client query messages. Default is no. These are
client queries to Unbound.
dnstap-log-client-response-messages: <yes or no>
Enable to log client response messages. Default is no. These
are responses from Unbound to clients.
dnstap-log-forwarder-query-messages: <yes or no>
Enable to log forwarder query messages. Default is no.
dnstap-log-forwarder-response-messages: <yes or no>
Enable to log forwarder response messages. Default is no.
Response Policy Zone Options
Response Policy Zones are configured with rpz:, and each one must have
a name:. There can be multiple ones, by listing multiple rpz clauses,
each with a different name. RPZ clauses are applied in order of
configuration. The respip module needs to be added to the module-
config, e.g.: module-config: "respip validator iterator".
QNAME, Response IP Address, nsdname, nsip and clientip triggers are
supported. Supported actions are: NXDOMAIN, NODATA, PASSTHRU, DROP,
Local Data, tcp-only and drop. RPZ QNAME triggers are applied after
local-zones and before auth-zones.
The rpz zone is formatted with a SOA start record as usual. The items
in the zone are entries, that specify what to act on (the trigger) and
what to do (the action). The trigger to act on is recorded in the
name, the action to do is recorded as the resource record. The names
all end in the zone name, so you could type the trigger names without
a trailing dot in the zonefile.
An example RPZ record, that answers example.com with NXDOMAIN
example.com CNAME .
The triggers are encoded in the name on the left
name query name
netblock.rpz-client-ip client IP address
netblock.rpz-ip response IP address in the answer
name.rpz-nsdname nameserver name
netblock.rpz-nsip nameserver IP address
The netblock is written as <netblocklen>.<ip address in reverse>. For
IPv6 use 'zz' for '::'. Specify individual addresses with scope
length of 32 or 128. For example, 24.10.100.51.198.rpz-ip is
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198.51.100.10/24 and 32.10.zz.db8.2001.rpz-ip is
2001:db8:0:0:0:0:0:10/32.
The actions are specified with the record on the right
CNAME . nxdomain reply
CNAME *. nodata reply
CNAME rpz-passthru. do nothing, allow to continue
CNAME rpz-drop. the query is dropped
CNAME rpz-tcp-only. answer over TCP
A 192.0.2.1 answer with this IP address
Other records like AAAA, TXT and other CNAMEs (not rpz-..) can also be
used to answer queries with that content.
The RPZ zones can be configured in the config file with these settings
in the rpz: block.
name: <zone name>
Name of the authority zone.
primary: <IP address or host name>
Where to download a copy of the zone from, with AXFR and IXFR.
Multiple primaries can be specified. They are all tried if one
fails. To use a nondefault port for DNS communication append '@'
with the port number. You can append a '#' and a name, then AXFR
over TLS can be used and the tls authentication certificates will
be checked with that name. If you combine the '@' and '#', the
'@' comes first. If you point it at another Unbound instance, it
would not work because that does not support AXFR/IXFR for the
zone, but if you used url: to download the zonefile as a text
file from a webserver that would work. If you specify the
hostname, you cannot use the domain from the zonefile, because it
may not have that when retrieving that data, instead use a plain
IP address to avoid a circular dependency on retrieving that IP
address.
master: <IP address or host name>
Alternate syntax for primary.
url: <url to zonefile>
Where to download a zonefile for the zone. With http or https.
An example for the url is
"http://www.example.com/example.org.zone". Multiple url
statements can be given, they are tried in turn. If only urls
are given the SOA refresh timer is used to wait for making new
downloads. If also primaries are listed, the primaries are first
probed with UDP SOA queries to see if the SOA serial number has
changed, reducing the number of downloads. If none of the urls
work, the primaries are tried with IXFR and AXFR. For https, the
tls-cert-bundle and the hostname from the url are used to
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authenticate the connection.
allow-notify: <IP address or host name
With allow-notify you can specify additional sources of notifies.
When notified, the server attempts to first probe and then zone
transfer. If the notify is from a primary, it first attempts
that primary. Otherwise other primaries are attempted. If there
are no primaries, but only urls, the file is downloaded when
notified. The primaries from primary: and url: statements are
allowed notify by default.
zonefile: <filename>
The filename where the zone is stored. If not given then no
zonefile is used. If the file does not exist or is empty,
Unbound will attempt to fetch zone data (eg. from the primary
servers).
rpz-action-override: <action>
Always use this RPZ action for matching triggers from this zone.
Possible action are: nxdomain, nodata, passthru, drop, disabled
and cname.
rpz-cname-override: <domain>
The CNAME target domain to use if the cname action is configured
for rpz-action-override.
rpz-log: <yes or no>
Log all applied RPZ actions for this RPZ zone. Default is no.
rpz-log-name: <name>
Specify a string to be part of the log line, for easy
referencing.
rpz-signal-nxdomain-ra: <yes or no>
Signal when a query is blocked by the RPZ with NXDOMAIN with an
unset RA flag. This allows certain clients, like dnsmasq, to
infer that the domain is externally blocked. Default is no.
for-downstream: <yes or no>
If enabled the zone is authoritatively answered for and queries
for the RPZ zone information are answered to downstream clients.
This is useful for monitoring scripts, that can then access the
SOA information to check if the rpz information is up to date.
Default is no.
tags: <list of tags>
Limit the policies from this RPZ clause to clients with a
matching tag. Tags need to be defined in define-tag and can be
assigned to client addresses using access-control-tag. Enclose
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list of tags in quotes ("") and put spaces between tags. If no
tags are specified the policies from this clause will be applied
for all clients.
MEMORY CONTROL EXAMPLE
In the example config settings below memory usage is reduced. Some
service levels are lower, notable very large data and a high TCP load
are no longer supported. Very large data and high TCP loads are
exceptional for the DNS. DNSSEC validation is enabled, just add trust
anchors. If you do not have to worry about programs using more than 3
Mb of memory, the below example is not for you. Use the defaults to
receive full service, which on BSD-32bit tops out at 30-40 Mb after
heavy usage.
# example settings that reduce memory usage
server:
num-threads: 1
outgoing-num-tcp: 1 # this limits TCP service, uses less buffers.
incoming-num-tcp: 1
outgoing-range: 60 # uses less memory, but less performance.
msg-buffer-size: 8192 # note this limits service, 'no huge stuff'.
msg-cache-size: 100k
msg-cache-slabs: 1
rrset-cache-size: 100k
rrset-cache-slabs: 1
infra-cache-numhosts: 200
infra-cache-slabs: 1
key-cache-size: 100k
key-cache-slabs: 1
neg-cache-size: 10k
num-queries-per-thread: 30
target-fetch-policy: "2 1 0 0 0 0"
harden-large-queries: "yes"
harden-short-bufsize: "yes"
FILES
/usr/local/etc/unbound
default Unbound working directory.
/usr/local/etc/unbound
default chroot(2) location.
/usr/local/etc/unbound/unbound.conf
Unbound configuration file.
/usr/local/etc/unbound/unbound.pid
default Unbound pidfile with process ID of the running daemon.
unbound.log
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Unbound log file. default is to log to syslog(3).
SEE ALSO
unbound(8), unbound-checkconf(8).
AUTHORS
Unbound was written by NLnet Labs. Please see CREDITS file in the
distribution for further details.
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