UNBOUND.CONF(5) Unbound UNBOUND.CONF(5)
NAME
unbound.conf - Unbound 1.24.0 configuration file.
SYNOPSIS
unbound.conf
DESCRIPTION
unbound.conf is used to configure unbound(8). The file format has at-
tributes 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 ig-
nored 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/un-
bound.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
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 any-
where, 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 in-
cluded files works, relative pathnames for the included names work if
the directory where the daemon is started equals its chroot/working di-
rectory 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 level.
Level 0
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.
The verbosity can also be increased from the command line and
during run time via remote control. See unbound(8) and
unbound-control(8) respectively.
Default: 1
statistics-interval: <seconds>
The number of seconds between printing statistics to the log for
every thread. Disable with value 0 or "". The histogram sta-
tistics are only printed if replies were sent during the statis-
tics interval, requestlist statistics are printed for every in-
terval (but can be 0). This is because the median calculation
requires data to be present.
Default: 0 (disabled)
statistics-cumulative: <yes or no>
If enabled, statistics are cumulative since starting Unbound,
without clearing the statistics counters after logging the sta-
tistics.
Default: no
extended-statistics: <yes or no>
If enabled, extended statistics are printed from
unbound-control(8). The counters are listed in
unbound-control(8). Keeping track of more statistics takes
time.
Default: no
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 PRZ
actions.
Default: yes
num-threads: <number>
The number of threads to create to serve clients. Use 1 for no
threading.
Default: 1
port: <port number>
The port number on which the server responds to queries.
Default: 53
interface: <IP address or interface name[@port]>
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 on lo-
calhost.
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 be-
tween interface and port number), if not specified the default
port (from port) is used.
ip-address: <IP address or interface name[@port]>
Same as interface (for ease of compatibility with nsd.conf(5)).
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 se-
lect which (future) interfaces Unbound provides service on.
This feature is experimental, and needs support in your OS for
particular socket options.
Default: 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.
This can be used to have interface automatic to deal with the
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.
Default: ""
outgoing-interface: <IPv4/IPv6 address or IPv6 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 inter-
faces. 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 ad-
dress taken from the netblock to counter spoofing. Requires the
IPv6 netblock to be routed to the host running Unbound, and re-
quires 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 com-
mands 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 com-
pile options. Larger numbers need extra resources from the op-
erating system. For performance a very large value is best, use
libevent to make this possible.
Default: 4096 (libevent) / 960 (minievent) / 48 (windows)
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 in-
creases 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 per-
mitted ports and subtracting the avoided ports from the set of
allowed ports. The processing starts with the non IANA allo-
cated ports above 1024 in the set of allowed ports.
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 IPv4 and IPv6. 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. If set
to 0, or if do-tcp: no is set, no TCP queries to authoritative
servers are done. For larger installations increasing this
value is a good idea.
Default: 10
incoming-num-tcp: <number>
Number of incoming TCP buffers to allocate per thread. If set
to 0, or if do-tcp: no is set, no TCP queries from clients are
accepted. For larger installations increasing this value is a
good idea.
Default: 10
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.
Setting to 512 bypasses even the most stringent path MTU prob-
lems, but is seen as extreme, since the amount of TCP fallback
generated is excessive (probably also for this resolver, con-
sider tuning outgoing-num-tcp).
Default: 1232 (DNS Flag Day 2020 recommendation)
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: 1232 (same as edns-buffer-size)
stream-wait-size: <number>
Number of bytes size maximum to use for waiting stream buffers.
A plain number is in bytes, append 'k', 'm' or 'g' for kilo-
bytes, 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, oth-
erwise 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 fur-
ther requests waiting in TCP buffers.
Default: 4m
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 re-
duced 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.
Default: 65552
msg-cache-size: <number>
Number of bytes size of the message cache. A plain number is in
bytes, append 'k', 'm' or 'g' for kilobytes, megabytes or giga-
bytes (1024*1024 bytes in a megabyte).
Default: 4m
msg-cache-slabs: <number>
Number of slabs in the message cache. Slabs reduce lock con-
tention by threads. Must be set to a power of 2. Setting
(close) to the number of cpus is a fairly good setting. If left
unconfigured, it will be configured automatically to be a power
of 2 close to the number of configured threads in multi-threaded
environments.
Default: (unconfigured)
num-queries-per-thread: <number>
The number of queries that every thread will service simultane-
ously. 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.
Default: 2048 (libevent) / 512 (minievent) / 24 (windows)
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.
The effect is that the qps for long-lasting queries is about:
(num-queries-per-thread / 2) / (average time for such long queries) qps
The qps for short queries can be about:
(num-queries-per-thread / 2) / (jostle-timeout in whole seconds) qps per thread
about (2048/2)*5 = 5120 qps by default.
Default: 200
delay-close: <msec>
Extra delay for timeouted UDP ports before they are closed, in
msec. This prevents very delayed answer packets from the up-
stream (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.
Default: 0 (disabled)
udp-connect: <yes or no>
Perform connect(2) for UDP sockets that mitigates ICMP side
channel leakage.
Default: yes
unknown-server-time-limit: <msec>
The wait time in msec for waiting for an unknown server to re-
ply. 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: 376
discard-timeout: <msec>
The wait time in msec where recursion requests are dropped.
This is to stop a large number of replies from accumulating.
They receive no reply, the work item continues to recurse. It
is nice to be a bit larger than serve-expired-client-timeout if
that is enabled. A value of 1900 msec is suggested. The value
0 disables it.
Default: 1900
wait-limit: <number>
The number of replies that can wait for recursion, for an IP ad-
dress. This makes a ratelimit per IP address of waiting replies
for recursion. It stops very large amounts of queries waiting
to be returned to one destination. The value 0 disables wait
limits.
Default: 1000
wait-limit-cookie: <number>
The number of replies that can wait for recursion, for an IP ad-
dress that sent the query with a valid DNS Cookie. Since the
cookie validates the client address, this limit can be higher.
Default: 10000
wait-limit-netblock: <netblock> <number>
The wait limit for the netblock. If not given the wait-limit
value is used. The most specific netblock is used to determine
the limit. Useful for overriding the default for a specific,
group or individual, server. The value -1 disables wait limits
for the netblock. By default the loopback has a wait limit net-
block of -1, it is not limited, because it is separated from the
rest of network for spoofed packets. The loopback addresses
127.0.0.0/8 and ::1/128 are default at -1.
Default: (none)
wait-limit-cookie-netblock: <netblock> <number>
The wait limit for the netblock, when the query has a DNS
Cookie. If not given, the wait-limit-cookie value is used. The
value -1 disables wait limits for the netblock. The loopback
addresses 127.0.0.0/8 and ::1/128 are default at -1.
Default: (none)
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 net-
stat -su). 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 permis-
sion 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.
Default: 0 (use system value)
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. If set to 0 it uses the system value. Specify the number
of bytes to ask for, try "8m" on a very busy server.
It needs some space to be able to deal with packets that wait
for local address resolution, from like ARP and NDP discovery,
before they are sent out, hence it is elevated above the system
default by default.
The OS caps it at a maximum, on linux Unbound needs root permis-
sion to bypass the limit, or the admin can use sysctl
net.core.wmem_max.
On BSD, Solaris changes are similar to so-rcvbuf.
Default: 4m
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.
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 contin-
ues 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).
Default: yes
ip-transparent: <yes or no>
If yes, then use IP_TRANSPARENT socket option on sockets where
Unbound is listening for incoming traffic. Allows you to bind
to non-local interfaces. For example for non-existent IP ad-
dresses 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 (fu-
ture) 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.
Default: no
ip-freebind: <yes or no>
If yes, then use IP_FREEBIND socket option on sockets where Un-
bound is listening to incoming traffic. 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.
Default: no
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. A plain number is in
bytes, append 'k', 'm' or 'g' for kilobytes, megabytes or giga-
bytes (1024*1024 bytes in a megabyte).
Default: 4m
rrset-cache-slabs: <number>
Number of slabs in the RRset cache. Slabs reduce lock con-
tention by threads. Must be set to a power of 2. Setting
(close) to the number of cpus is a fairly good setting. If left
unconfigured, it will be configured automatically to be a power
of 2 close to the number of configured threads in multi-threaded
environments.
Default: (unconfigured)
cache-max-ttl: <seconds>
Time to live maximum for RRsets and messages in the cache. 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.
Default: 86400 (1 day)
cache-min-ttl: <seconds>
Time to live minimum for RRsets and messages in the cache. If
the minimum kicks in, the data is cached for longer than the do-
main owner intended, and thus less queries are made to look up
the data. Zero makes sure the data in the cache is as the do-
main 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.
Default: 0 (disabled)
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. This applies to
NXDOMAIN and NODATA answers.
Default: 3600
cache-min-negative-ttl: <seconds>
Time to live minimum for negative responses, these have a SOA in
the authority section that is limited in time. If this is dis-
abled and cache-min-ttl is configured, it will take effect in-
stead. In that case you can set this to 1 to honor the upstream
TTL. This applies to NXDOMAIN and NODATA answers.
Default: 0 (disabled)
infra-host-ttl: <seconds>
Time to live for entries in the host cache. The host cache con-
tains roundtrip timing, lameness and EDNS support information.
Default: 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. Setting
(close) to the number of cpus is a fairly good setting. If left
unconfigured, it will be configured automatically to be a power
of 2 close to the number of configured threads in multi-threaded
environments.
Default: (unconfigured)
infra-cache-numhosts: <number>
Number of hosts for which information is cached.
Default: 10000
infra-cache-min-rtt: <msec>
Lower limit for dynamic retransmit timeout calculation in infra-
structure cache. Increase this value if using forwarders need-
ing more time to do recursive name resolution.
Default: 50
infra-cache-max-rtt: <msec>
Upper limit for dynamic retransmit timeout calculation in infra-
structure cache.
Default: 120000 (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. 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.
Default: no
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 IPv4 queries are answered or issued.
Default: yes
do-ip6: <yes or no>
Enable or disable whether IPv6 queries are answered or issued.
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 DNS traffic, it
does not impact the contents of the DNS traffic, which may have
IPv4 (A) and IPv6 (AAAA) addresses in it.
Default: yes
prefer-ip4: <yes or no>
If enabled, prefer IPv4 transport for sending DNS queries to in-
ternet nameservers. Useful if the IPv6 netblock the server has,
the entire /64 of that is not owned by one operator and the rep-
utation of the netblock /64 is an issue, using IPv4 then uses
the IPv4 filters that the upstream servers have.
Default: no
prefer-ip6: <yes or no>
If enabled, prefer IPv6 transport for sending DNS queries to in-
ternet nameservers.
Default: no
do-udp: <yes or no>
Enable or disable whether UDP queries are answered or issued.
Default: yes
do-tcp: <yes or no>
Enable or disable whether TCP queries are answered or issued.
Default: yes
tcp-mss: <number>
Maximum segment size (MSS) of TCP socket on which the server re-
sponds 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 in-
terface 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. When the
number of free incoming TCP buffers falls below 50% of the total
number configured, the option value used is progressively re-
duced, 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 200 milliseconds is observed regardless of
the option value used. It will be overridden by
edns-tcp-keepalive-timeout if edns-tcp-keepalive is enabled.
Default: 30000 (30 seconds)
tcp-reuse-timeout: <msec>
The period Unbound will keep TCP persistent connections open to
authority servers.
Default: 60000 (60 seconds)
max-reuse-tcp-queries: <number>
The maximum number of queries that can be sent on a persistent
TCP connection.
Default: 200
tcp-auth-query-timeout: <number>
Timeout in milliseconds for TCP queries to auth servers.
Default: 3000 (3 seconds)
edns-tcp-keepalive: <yes or no>
Enable or disable EDNS TCP Keepalive.
Default: no
edns-tcp-keepalive-timeout: <msec>
Overrides tcp-idle-timeout when edns-tcp-keepalive is enabled.
If the client supports the EDNS TCP Keepalive option, If the
client supports the EDNS TCP Keepalive option, Unbound sends the
timeout value to the client to encourage it to close the connec-
tion before the server times out.
Default: 120000 (2 minutes)
sock-queue-timeout: <sec>
UDP queries that have waited in the socket buffer for a long
time can be dropped. 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. The socket option is available on the Linux and
FreeBSD platforms.
Default: 0 (disabled)
tcp-upstream: <yes or no>
Enable or disable whether the upstream queries use TCP only for
transport. 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.
Default: no
udp-upstream-without-downstream: <yes or no>
Enable UDP upstream even if do-udp: no is set. Useful for TLS
service providers, that want no UDP downstream but use UDP to
fetch data upstream.
Default: no (no changes)
tls-upstream: <yes or no>
Enabled or disable whether the upstream queries use TLS only for
transport. 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. If
the tls-upstream option is enabled, it is for all the forwards
and stubs, where the forward-tls-upstream and stub-tls-upstream
options are ignored, as if they had been set to yes.
Default: no
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 con-
tain 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. Enabling or disabling this ser-
vice 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.
NOTE:
Unbound needs to be compiled with libnghttp2 in order to pro-
vide DNS-over-HTTPS.
Default: "" (disabled)
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: "" (disabled)
ssl-service-pem: <file>
Alternate syntax for tls-service-pem.
tls-port: <number>
The port number on which to provide TCP TLS service. Only in-
terfaces configured with that port number as @number get the TLS
service.
Default: 853
ssl-port: <number>
Alternate syntax for tls-port.
tls-cert-bundle: <file>
If null or "", no file is used. Set it to the certificate bun-
dle 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 permis-
sion drop and chroot.
Default: "" (disabled)
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 certifi-
cates. 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.
Default: no
tls-system-cert: <yes or no>
This the same attribute as the tls-win-cert attribute, under a
different name. Because it is not windows specific.
tls-additional-port: <portnr>
List port numbers 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 Un-
bound server. These files contain the secret key for the TLS
session tickets. First key use to encrypt and decrypt TLS ses-
sion 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.
Default: ""
tls-ciphers: <string with cipher list>
Set the list of ciphers to allow when serving TLS. Use "" for
default ciphers.
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 default ciphersuites.
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: 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: 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: yes
pad-queries-block-size: <number>
The block size with which to pad queries sent over TLS up-
streams.
Default: 128
tls-use-sni: <yes or no>
Enable or disable sending the SNI extension on TLS connections.
NOTE:
Changing the value requires a reload.
Default: yes
https-port: <number>
The port number on which to provide DNS-over-HTTPS service.
Only interfaces configured with that port number as @number get
the HTTPS service.
Default: 443
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 com-
bined. These buffers contain (partial) DNS queries waiting for
request stream completion. An RST_STREAM frame will be send to
streams exceeding this limit. A plain number is in bytes, ap-
pend 'k', 'm' or 'g' for kilobytes, megabytes or gigabytes
(1024*1024 bytes in a megabyte).
Default: 4m
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. A plain number is in bytes,
append 'k', 'm' or 'g' for kilobytes, megabytes or gigabytes
(1024*1024 bytes in a megabyte).
Default: 4m
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: 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: 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 de-
nied/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, DoQ or DNSCrypt lis-
tening interface.
Can list multiple, each on a new statement.
quic-port: <number>
The port number on which to provide DNS-over-QUIC service. Only
interfaces configured with that port number as @number get the
QUIC service. The interface uses QUIC for the UDP traffic on
that port number.
Default: 853
quic-size: <size in bytes>
Maximum number of bytes for all QUIC buffers and data combined.
A plain number is in bytes, append 'k', 'm' or 'g' for kilo-
bytes, megabytes or gigabytes (1024*1024 bytes in a megabyte).
New connections receive connection refused when the limit is ex-
ceeded. New streams are reset when the limit is exceeded.
Default: 8m
use-systemd: <yes or no>
Enable or disable systemd socket activation.
Default: 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: 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.
Default: (disabled)
access-control: <IP netblock> <action>
Specify treatment of incoming queries from their originating IP
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 pos-
sible to give the statement several times in order to specify
the treatment of different netblocks. The netblock is given as
an IPv4 or IPv6 address with /size appended for a classless net-
work block. The most specific netblock match is used, if none
match refuse is used. The order of the access-control state-
ments therefore does not matter. The action can be deny,
refuse, allow, allow_setrd, allow_snoop, allow_cookie,
deny_non_local or refuse_non_local.
deny Stops queries from hosts from that netblock.
refuse Stops queries too, but sends a DNS rcode REFUSED error
message back.
allow Gives access to clients from that netblock. It gives
only access for recursion clients (which is what almost
all clients need). Non-recursive queries are refused.
The allow action does allow non-recursive queries to ac-
cess 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 non-recursive
queries are made for the authoritative data. For non-re-
cursive queries any replies from the dynamic cache are
refused.
allow_setrd
Ignores the recursion desired (RD) bit and treats all re-
quests 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 re-
solver DNS server, but only supports stub domains and
sends queries to the resolver DNS server with the RD bit
cleared.
allow_snoop
Gives non-recursive access too. This gives both recur-
sive and non recursive access. The name allow_snoop
refers to cache snooping, a technique to use non-recur-
sive queries to examine the cache contents (for malicious
acts). However, non-recursive 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.
allow_cookie
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 con-
taining 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, re-
gardless 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.
deny_non_local
The deny_non_local action is for hosts that are only al-
lowed to query for the authoritative local-data, they are
not allowed full recursion but only the static data.
Messages that are disallowed are dropped.
refuse_non_local
The refuse_non_local action is for hosts that are only
allowed to query for the authoritative local-data, they
are not allowed full recursion but only the static data.
Messages that are disallowed receive error code REFUSED.
By default only localhost (the 127.0.0.0/8 IP netblock, not the
loopback interface) is implicitly 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.
access-control-tag: <IP netblock> "<list of tags>"
Assign tags to access-control elements. Clients using this ac-
cess control element use localzones that are tagged with one of
these tags.
Tags must be defined in define-tag. 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 ac-
tion 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 string>"
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 [@port]> <action>
Similar to access-control but for interfaces.
The action is the same as the ones defined under access-control.
Default action for interfaces is refuse. By default only local-
host (the 127.0.0.0/8 IP netblock, not the loopback interface)
is implicitly allowed through the default access-control behav-
ior. This also means that any attempt to use the interface-*:
options for the loopback interface will not work as they will be
overridden by the implicit default "access-control: 127.0.0.0/8
allow" option.
NOTE:
The interface needs to be already specified with interface
and that any access-control*: attribute overrides all inter-
face-*: attributes for targeted clients.
interface-tag: <ip address or interface name [@port]> <"list of tags">
Similar to access-control-tag but for interfaces.
NOTE:
The interface needs to be already specified with interface
and that any access-control*: attribute overrides all inter-
face-*: attributes for targeted clients.
interface-tag-action: <ip address or interface name [@port]> <tag> <ac-
tion>
Similar to access-control-tag-action but for interfaces.
NOTE:
The interface needs to be already specified with interface
and that any access-control*: attribute overrides all inter-
face-*: attributes for targeted clients.
interface-tag-data: <ip address or interface name [@port]> <tag> <"re-
source record string">
Similar to access-control-tag-data but for interfaces.
NOTE:
The interface needs to be already specified with interface
and that any access-control*: attribute overrides all inter-
face-*: attributes for targeted clients.
interface-view: <ip address or interface name [@port]> <view name>
Similar to access-control-view but for interfaces.
NOTE:
The interface needs to be already specified with interface
and that any access-control*: attribute overrides all inter-
face-*: attributes 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 re-
load.
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 di-
rectory, or as an absolute path relative to the original root.
In the last case the path is adjusted to remove the unused por-
tion.
The pidfile can be either a relative path to the working direc-
tory, or an absolute path relative to the original root. It is
written just prior to chroot and dropping permissions. This al-
lows the pidfile to be /var/run/unbound.pid and the chroot to be
/var/unbound, for example. Note that Unbound is not able to re-
move the pidfile after termination when it is located outside of
the chroot directory.
Additionally, Unbound may need to access /dev/urandom (for en-
tropy) from inside the chroot.
If given, a chroot(2) is done to the given directory. If you
give "" no chroot(2) is performed.
Default: /usr/local/etc/unbound
username: <name>
If given, after binding the port the user privileges are
dropped. 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 re-
quires privileges, then a reload will fail; a restart is needed.
Default: unbound
directory: <directory>
Sets the working directory for the program. On Windows the
string "%EXECUTABLE%" tries to change to the directory that un-
bound.exe resides in. If you give a server: directory: <direc-
tory> before include file statements then those includes can be
relative to the working directory.
Default: /usr/local/etc/unbound
logfile: <filename>
If "" is given, logging goes to stderr, or nowhere once daemo-
nized. 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 attribute is internally
set to no.
The logfile is reopened (for append) when the config file is
reread, on SIGHUP.
Default: "" (disabled)
use-syslog: <yes or no>
Sets Unbound to send log messages to the syslogd, using sys-
log(3). The log facility LOG_DAEMON is used, with identity "un-
bound". The logfile setting is overridden when use-syslog: yes
is set.
Default: yes
log-identity: <string>
If "" is given, then the name of the executable, usually "un-
bound" 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.
Default: ""
log-time-ascii: <yes or no>
Sets logfile lines to use a timestamp in UTC ASCII. No effect
if using syslog, in that case syslog formats the timestamp
printed into the log files.
Default: no (prints the seconds since 1970 in brackets)
log-time-iso: <yes or no>
Log time in ISO8601 format, if log-time-ascii: yes is also set.
Default: no
log-queries: <yes or no>
Prints one line per query to the log, with the log timestamp and
IP address, name, type and class. Note that it takes time to
print these lines which makes the server (significantly) slower.
Odd (nonprintable) characters in names are printed as '?'.
Default: no
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. Note that it takes time to print
these lines which makes the server (significantly) slower. Odd
(nonprintable) characters in names are printed as '?'.
Default: no
log-tag-queryreply: <yes or no>
Prints the word 'query' and 'reply' with log-queries and
log-replies. This makes filtering logs easier.
Default: no (backwards compatible)
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.
Default: no
log-local-actions: <yes or no>
Print log lines to inform about local zone actions. These lines
are like the local-zone type inform print outs, but they are
also printed for the other types of local zones.
Default: no
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.
Default: no
pidfile: <filename>
The process id is written to the file. Default is "/usr/lo-
cal/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.
Default: /usr/local/etc/unbound/unbound.pid
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 de-
fault may become outdated, when servers change, therefore it is
good practice to use a root hints file.
Default: ""
hide-identity: <yes or no>
If enabled 'id.server' and 'hostname.bind' queries are REFUSED.
Default: no
identity: <string>
Set the identity to report. If set to "", then the hostname of
the server is returned.
Default: ""
hide-version: <yes or no>
If enabled 'version.server' and 'version.bind' queries are RE-
FUSED.
Default: no
version: <string>
Set the version to report. If set to "", then the package ver-
sion is returned.
Default: ""
hide-http-user-agent: <yes or no>
If enabled the HTTP header User-Agent is not set. Use with cau-
tion as some webserver configurations may reject HTTP requests
lacking this header. If needed, it is better to explicitly set
the http-user-agent below.
Default: no
http-user-agent: <string>
Set the HTTP User-Agent header for outgoing HTTP requests. If
set to "", then the package name and version are used.
Default: ""
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.
Default: (disabled)
hide-trustanchor: <yes or no>
If enabled 'trustanchor.unbound' queries are REFUSED.
Default: no
target-fetch-policy: <"list of numbers">
Set the target fetch policy used by Unbound to determine if it
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 num-
bers. 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.
Default: "3 2 1 0 0"
harden-short-bufsize: <yes or no>
Very small EDNS buffer sizes from queries are ignored.
Default: yes (as described in the standard)
harden-large-queries: <yes or no>
Very large queries are ignored. Default is no, since it is le-
gal protocol wise to send these, and could be necessary for op-
eration if TSIG or EDNS payload is very large.
Default: no
harden-glue: <yes or no>
Will trust glue only if it is within the servers authority.
Default: yes
harden-unverified-glue: <yes or no>
Will trust only in-zone glue. Will try to resolve all out of
zone (unverified) glue. Will fallback to the original glue if
unable to resolve.
Default: no
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 at-
tack that disables security for a zone.
Default: yes
harden-below-nxdomain: <yes or no>
From RFC 8020 (with title "NXDOMAIN: There Really Is Nothing Un-
derneath"), returns NXDOMAIN to queries for a name below another
name that is already known to be NXDOMAIN. DNSSEC mandates NO-
ERROR for empty nonterminals, hence this is possible. Very old
software might return NXDOMAIN for empty nonterminals (that usu-
ally happen for reverse IP address lookups), and thus may be in-
compatible with this. To try to avoid this only DNSSEC-secure
NXDOMAINs are used, because the old software does not have
DNSSEC.
NOTE:
The NXDOMAIN must be secure, this means NSEC3 with optout is
insufficient.
Default: yes
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 vali-
dation on nameserver NS sets and the nameserver addresses that
are encountered on the referral path to the answer. Default is
off, 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.
Default: no
harden-algo-downgrade: <yes or no>
Harden against algorithm downgrade when multiple algorithms are
advertised in the DS record. This works by first choosing only
the strongest DS digest type as per RFC 4509 (Unbound treats the
highest algorithm as the strongest) and then expecting signa-
tures from all the advertised signing algorithms from the chosen
DS(es) to be present. If no, allows any one supported algorithm
to validate the zone, even if other advertised algorithms are
broken. RFC 6840 mandates that zone signers must produce zones
signed with all advertised algorithms, but sometimes they do
not. RFC 6840 also clarifies that this requirement is not for
validators and validators should accept any single valid path.
It should thus be explicitly noted that this option violates RFC
6840 for DNSSEC validation and should only be used to perform a
signature completeness test to support troubleshooting.
WARNING:
Using this option may break DNSSEC resolution with non RFC
6840 conforming signers and/or in multi-signer configurations
that don't send all the advertised signatures.
Default: no
harden-unknown-additional: <yes or no>
Harden against unknown records in the authority section and ad-
ditional section. If no, such records are copied from the up-
stream and presented to the client together with the answer. If
yes, it could hamper future protocol developments that want to
add records.
Default: no
use-caps-for-id: <yes or no>
Use 0x20-encoded random bits in the query to foil spoof at-
tempts. This perturbs the lowercase and uppercase of query
names sent to authority servers and checks if the reply still
has the correct casing. This feature is an experimental imple-
mentation of draft dns-0x20.
Default: no
caps-exempt: <domain>
Exempt the domain so that it does not receive caps-for-id per-
turbed 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 dif-
ferent domains.
caps-whitelist: <domain>
Alternate syntax for caps-exempt.
qname-minimisation: <yes or no>
Send minimum amount of information to upstream servers to en-
hance privacy. Only send minimum required labels of the QNAME
and set QTYPE to A when possible. Best effort approach; full
QNAME and original QTYPE will be sent when upstream replies with
a RCODE other than NOERROR, except when receiving NXDOMAIN from
a DNSSEC signed zone.
Default: 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: no
aggressive-nsec: <yes or no>
Aggressive NSEC uses the DNSSEC NSEC chain to synthesize NXDO-
MAIN and other denials, using information from previous NXDO-
MAINs answers. It helps to reduce the query rate towards tar-
gets that get a very high nonexistent name lookup rate.
Default: yes
private-address: <IP address or subnet>
Give IPv4 of IPv6 addresses or classless subnets. These are ad-
dresses on your private network, and are not allowed to be re-
turned for public internet names. Any occurrence of such ad-
dresses 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 RFC 1918 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 inter-
net.
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 ad-
dresses. Give multiple times to allow multiple domain names to
contain private addresses.
Default: (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 ac-
tion is to clear the rrset and message caches, hopefully flush-
ing away any poison. A value of 10 million is suggested.
Default: 0 (disabled)
do-not-query-address: <IP address>
Do not query the given IP address. Can be IPv4 or IPv6. Append
/num to indicate a classless delegation netblock, for example
like 10.2.3.4/24 or 2001::11/64.
Default: (none)
do-not-query-localhost: <yes or no>
If yes, localhost is added to the do-not-query-address entries,
both IPv6 ::1 and IPv4 127.0.0.1/8. If no, then localhost can
be used to send queries to.
Default: yes
prefetch: <yes or no>
If yes, cache hits on message cache elements that are on their
last 10 percent of their TTL value trigger a prefetch to keep
the cache up to date. Turning it on gives about 10 percent more
traffic and load on the machine, but popular items do not expire
from the cache.
Default: no
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 re-
quests. It does use a little more CPU. Also if the cache is
set to 0, it is no use.
Default: no
deny-any: <yes or no>
If yes, deny queries of type ANY with an empty response. 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.
Default: no
rrset-roundrobin: <yes or no>
If yes, Unbound rotates RRSet order in response (the random num-
ber is taken from the query ID, for speed and thread safety).
Default: 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 which may cause a slight speedup.
The default is yes, even though the DNS protocol RFCs mandate
these sections, and the additional content could save roundtrips
for clients that use the additional content. However these sec-
tions are hardly used by clients. Enabling prefetch can benefit
clients that need the additional content by trying to keep that
content fresh in the cache.
Default: yes
disable-dnssec-lame-check: <yes or no>
If yes, disables the DNSSEC lameness check in the iterator.
This check sees if RRSIGs are present in the answer, when DNSSEC
is expected, and retries another authority if RRSIGs are unex-
pectedly missing. The validator will insist in RRSIGs for
DNSSEC signed domains regardless of this setting, if a trust an-
chor is loaded.
Default: no
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 be-
low).
NOTE:
The ordering of the modules is significant, the order decides
the order of processing.
Setting this to just "iterator" will result in a non-validating
server. Setting this to "validator iterator" will turn on
DNSSEC validation.
NOTE:
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.
Most modules that need to be listed here have to be listed at
the beginning of the line.
The subnetcache module has to be listed just before the itera-
tor.
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.
Default: "validator iterator"
trust-anchor-file: <filename>
File with trusted keys for validation. Both DS and DNSKEY en-
tries can appear in the file. The format of the file is the
standard DNS Zone file format.
Default: "" (no trust anchor file)
auto-trust-anchor-file: <filename>
File with trust anchor for one zone, which is tracked with RFC
5011 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).
Default: "" (no auto trust anchor file)
trust-anchor: "<Resource Record>"
A DS or DNSKEY RR for a key to use for validation. Multiple en-
tries can be given to specify multiple trusted keys, in addition
to the trust-anchor-file. The resource record is entered in the
same format as dig(1) or drill(1) prints them, the 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.
Default: (none)
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.
Default: "" (no trusted keys file)
trust-anchor-signaling: <yes or no>
Send RFC 8145 key tag query after trust anchor priming.
Default: yes
root-key-sentinel: <yes or no>
Root key trust anchor sentinel.
Default: yes
domain-insecure: <domain name>
Sets <domain name> to be insecure, DNSSEC chain of trust is ig-
nored 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.
Default: (none)
val-override-date: <rrsig-style date spec>
WARNING:
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 signa-
ture inception and expiration. The value -1 ignores the date
altogether, useful for some special applications.
Default: 0 (disabled)
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 (expira-
tion - 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 signa-
tures.
Default: 3600 (1 hour)
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 (expira-
tion - 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.
Default: 86400 (24 hours)
val-max-restart: <number>
The maximum number the validator should restart validation with
another authority in case of failed validation.
Default: 5
val-bogus-ttl: <seconds>
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 in-
stead. The time interval prevents repeated revalidation of bo-
gus data.
Default: 60
val-clean-additional: <yes or no>
Instruct the validator to remove data from the additional sec-
tion of secure messages that are not signed properly. Messages
that are insecure, bogus, indeterminate or unchecked are not af-
fected. Use this setting to protect the users that rely on this
validator for authentication from potentially bad data in the
additional section.
Default: yes
val-log-level: <number>
Have the validator print validation failures to the log. Re-
gardless of the verbosity setting.
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 val-
idation 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.
Default: 0 (disabled)
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.
Default: no
ignore-cd-flag: <yes or no>
Instruct Unbound to ignore the CD flag from clients and refuse
to return bogus answers to them. Thus, the CD (Checking Dis-
abled) flag does not disable checking any more. This is useful
if legacy (w2008) servers that set the CD flag but cannot vali-
date DNSSEC themselves are the clients, and then Unbound pro-
vides them with DNSSEC protection.
Default: 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 informa-
tion. 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 al-
ready configured for DNSSEC validation (i.e., the validator mod-
ule is enabled; default) this option is implicitly turned off
with a warning as to not break DNSSEC validation in Unbound.
Default: 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. By de-
fault the expired answer will be used after a resolution attempt
errored out or is taking more than serve-expired-client-timeout
to resolve.
Default: 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
86400.
Default: 86400
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: 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).
Default: 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 immedi-
ately responding with expired data. Setting this to 0 will dis-
able this behavior and instead serve the expired record immedi-
ately from the cache before attempting to refresh it via resolu-
tion.
Default: 1800
serve-original-ttl: <yes or no>
If enabled, Unbound will always return the original TTL as re-
ceived from the upstream name server rather than the decrement-
ing 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:
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.
NOTE:
The values set using cache-min-ttl and cache-max-ttl are ig-
nored.
Default: no
val-nsec3-keysize-iterations: <"list of values">
List of keysize and iteration count values, separated by spaces,
surrounded by quotes. This determines the maximum allowed NSEC3
iteration count before a message is simply marked insecure in-
stead 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.
NOTE:
This table must be kept short; a very long list could cause
slower operation.
Default: "1024 150 2048 150 4096 150"
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: no
add-holddown: <seconds>
Instruct the auto-trust-anchor-file probe mechanism for RFC 5011
autotrust updates to add new trust anchors only after they have
been visible for this time.
Default: 2592000 (30 days as per the RFC)
del-holddown: <seconds>
Instruct the auto-trust-anchor-file probe mechanism for RFC 5011
autotrust updates to remove revoked trust anchors after they
have been kept in the revoked list for this long.
Default: 2592000 (30 days as per the RFC)
keep-missing: <seconds>
Instruct the auto-trust-anchor-file probe mechanism for RFC 5011
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
regular (non-5011) rollovers. The value 0 does not remove miss-
ing anchors, as per the RFC.
Default: 31622400 (366 days)
permit-small-holddown: <yes or no>
Debug option that allows the autotrust 5011 rollover timers to
assume very small values.
Default: no
key-cache-size: <number>
Number of bytes size of the key cache. A plain number is in
bytes, append 'k', 'm' or 'g' for kilobytes, megabytes or giga-
bytes (1024*1024 bytes in a megabyte).
Default: 4m
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 fairly good setting. If left unconfig-
ured, it will be configured automatically to be a power of 2
close to the number of configured threads in multi-threaded en-
vironments.
Default: (unconfigured)
neg-cache-size: <number>
Number of bytes size of the aggressive negative cache. A plain
number is in bytes, append 'k', 'm' or 'g' for kilobytes,
megabytes or gigabytes (1024*1024 bytes in a megabyte).
Default: 1m
unblock-lan-zones: <yes or no>
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 en-
abled, 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.
Default: no
insecure-lan-zones: <yes or no>
If enabled, then reverse lookups in private address space are
not validated. This is usually required whenever
unblock-lan-zones is used.
Default: no
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 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 informa-
tion. 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 an-
swered. 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 an-
swered. Otherwise if the query has a different name, the
query is resolved normally. If the query is for a name
given in local-data 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 an-
swered. 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 NO-
DATA reply for AAAA queries.
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
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 log-
file. The log message is:
timestamp, unbound-pid, info: zonename inform IP@port queryname type class.
This option can be used for normal resolution, but ma-
chines 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
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 lo-
cal data in the zone. Used for some block lists.
noview Breaks out of that view and moves towards the global lo-
cal 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 an-
swers. For when the view has view specific overrides but
some zone has to be answered from global local zone con-
tents.
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, resolver.arpa, service.arpa, onion, test, invalid and
the AS112 zones. The AS112 zones are reverse DNS zones for pri-
vate 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 IPv4 and IPv6 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:
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"
resolver.arpa (RFC 9462)
Default content:
local-zone: "resolver.arpa." static
local-data: "resolver.arpa. 10800 IN NS localhost."
local-data: "resolver.arpa. 10800 IN SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
service.arpa (draft-ietf-dnssd-srp-25)
Default content:
local-zone: "service.arpa." static
local-data: "service.arpa. 10800 IN NS localhost."
local-data: "service.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"
reverse local use zones (RFC 1918)
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.
special-use IPv4 Addresses (RFC 3330)
Reverse data for zones 0.in-addr.arpa (this),
254.169.in-addr.arpa (link-local), 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 (broadcast). And from
64.100.in-addr.arpa to 127.100.in-addr.arpa (Shared Ad-
dress Space).
reverse IPv6 unspecified (RFC 4291)
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 IPv6 Locally Assigned Local Addresses (RFC 4193)
Reverse data for zone D.F.ip6.arpa.
reverse IPv6 Link Local Addresses (RFC 4291)
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 lo-
cal-zone is configured. For record types such as TXT, use sin-
gle quotes, as in:
local-data: 'example. TXT "text"'
NOTE:
If you need more complicated authoritative data, with refer-
rals, 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 re-
versed 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 local zones. Tagged localzones will only be ap-
plied when the used access-control element has a matching tag.
Tags must be defined in define-tag. Enclose list of tags in
quotes ("") and put spaces between tags. When there are multi-
ple 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 local zone type for queries from addresses matching
netblock. Use this localzone type, regardless the type config-
ured for the local zone (both tagged and untagged) and regard-
less 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 condi-
tions as "the query matches it but there is no local data". Be-
cause 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 configura-
tion to be rejected as faulty. The deny action is non-condi-
tional, 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">. <"Re-
source 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 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-netblock>. 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 match-
ing rule is the same as that for access-control-tag and
local-zone. Unlike local-zone-tag, response-ip-tag can be de-
fined for an <IP-netblock> even if no response-ip is defined for
that netblock. If multiple response-ip-tag options are speci-
fied 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 "in-
valid" for response-ip listed above, since
access-control-tag-action 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 in-
stead of NXDOMAIN, since the response-ip data are inherently
type specific, and non-existence of data does not indicate any-
thing 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. 0 disables the feature. 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). Cached re-
sponses are not ratelimited by this setting.
This stops recursive floods, eg. random query names, but not
spoofed reflection floods. 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 random
names, and keeps unbound from sending traffic to the nameservers
for those zones.
NOTE:
Configured forwarders are excluded from ratelimiting.
Default: 0
ratelimit-size: <memory size>
Give the size of the data structure in which the current ongoing
rates are kept track in. In bytes or use m(mega), k(kilo),
g(giga). The ratelimit structure is small, so this data struc-
ture likely does not need to be large.
Default: 4m
ratelimit-slabs: <number>
Number of slabs in the ratelimit tracking data structure. Slabs
reduce lock contention by threads. Must be set to a power of 2.
Setting (close) to the number of cpus is a fairly good setting.
If left unconfigured, it will be configured automatically to be
a power of 2 close to the number of configured threads in
multi-threaded environments.
Default: (unconfigured)
ratelimit-factor: <number>
Set the amount of queries to rate limit when the limit is ex-
ceeded. If set to 0, all queries are dropped for domains where
the limit is exceeded. If set to another value, 1 in that num-
ber 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.
Default: 10
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, ex-
cept for ratelimit-factor, until demand decreases below the con-
figured ratelimit for a 2 second rate window. Useful to set
ratelimit to a suspicious rate to aggressively limit unusually
high traffic.
Default: no
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 differ-
ent settings for a top-level-domain and subdomains. A value of
0 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 com-
pletely dropped and will not receive a reply, SERVFAIL or other-
wise. 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: 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 re-
ply, SERVFAIL or otherwise. IP ratelimiting happens before
looking in the cache. This option could be useful in combina-
tion with allow_cookie, in an attempt to mitigate other amplifi-
cation attacks than UDP reflections (e.g., attacks targeting Un-
bound itself) which are already handled with DNS Cookies. If
used, the value is suggested to be higher than ip-ratelimit
e.g., tenfold.
Default: 0 (disabled)
ip-ratelimit-size: <memory size>
Give the size of the data structure in which the current ongoing
rates are kept track in. 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.
Default: 4m
ip-ratelimit-slabs: <number>
Number of slabs in the ip ratelimit tracking data structure.
Slabs reduce lock contention by threads. Must be set to a power
of 2. Setting (close) to the number of cpus is a fairly good
setting. If left unconfigured, it will be configured automati-
cally to be a power of 2 close to the number of configured
threads in multi-threaded environments.
Default: (unconfigured)
ip-ratelimit-factor: <number>
Set the amount of queries to rate limit when the limit is ex-
ceeded. 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.
Default: 10
ip-ratelimit-backoff: <yes or no>
If enabled, the rate limit 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, ex-
cept 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 unusu-
ally high traffic.
Default: no
outbound-msg-retry: <number>
The number of retries, per upstream nameserver in a delegation,
that Unbound will attempt in case a throwaway response is re-
ceived. 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: 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: 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: 11
iter-scrub-ns: <number>
Limit on the number of NS records allowed in an rrset of type
NS, from the iterator scrubber. This protects the internals of
the resolver from overly large NS sets.
Default: 20
iter-scrub-cname: <number>
Limit on the number of CNAME, DNAME records in an answer, from
the iterator scrubber. This protects the internals of the re-
solver from overly long indirection chains. Clips off the re-
mainder of the reply packet at that point.
Default: 11
max-global-quota: <number>
Limit on the number of upstream queries sent out for an incoming
query and its subqueries from recursion. It is not reset during
the resolution. When it is exceeded the query is failed and the
lookup process stops.
Default: 200
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.
Default: 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.
Default: 3
answer-cookie: <yes or no>
If enabled, Unbound will answer to requests containing DNS Cook-
ies as specified in RFC 7873 and RFC 9018.
Default: no
cookie-secret: "<128 bit hex string>"
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 exam-
ple hex string would be "000102030405060708090a0b0c0d0e0f".
NOTE:
This option is ignored if a cookie-secret-file is present.
In that case the secrets from that file are used in DNS
Cookie calculations.
Default: 128 bits random secret generated at startup time
cookie-secret-file: <filename>
File from which the secrets are read used in DNS Cookie calcula-
tions. When this file exists, the secrets in this file are used
and the secret specified by the cookie-secret option is ignored.
Enable it by setting a filename, like "/usr/local/etc/un-
bound_cookiesecrets.txt". The content of this file must be ma-
nipulated with the add_cookie_secret, drop_cookie_secret and
activate_cookie_secret commands to the unbound-control(8) tool.
Please see that manpage on how to perform a safe cookie secret
rollover.
Default: "" (disabled)
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: 65001
ede: <yes or no>
If enabled, Unbound will respond with Extended DNS Error codes
(RFC 8914). These EDEs provide additional information with a
response mainly for, but not limited to, DNS and DNSSEC errors.
When the val-log-level option is also set to 2, responses with
Extended DNS Errors concerning DNSSEC failures will also contain
a descriptive text message about the reason for the failure.
Default: no
ede-serve-expired: <yes or no>
If enabled, Unbound will attach an Extended DNS Error (RFC 8914)
Code 3 - Stale Answer as EDNS0 option to the expired response.
NOTE:
ede: yes needs to be set as well for this to work.
Default: no
dns-error-reporting: <yes or no>
If enabled, Unbound will send DNS Error Reports (RFC 9567). The
name servers need to express support by attaching the Re-
port-Channel EDNS0 option on their replies specifying the re-
porting agent for the zone. Any errors encountered during reso-
lution that would result in Unbound generating an Extended DNS
Error (RFC 8914) will be reported to the zone's reporting agent.
The ede option does not need to be enabled for this to work.
It is advised that the qname-minimisation option is also enabled
to increase privacy on the outgoing reports.
Default: no
Remote Control Options
In the remote-control: clause are the declarations for the remote con-
trol 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 un-
bound-control-setup(8) utility.
control-enable: <yes or no>
The option is used to enable remote control. If turned off, the
server does not listen for control commands.
Default: no
control-interface: <IP address or interface name or path>
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 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 config-
ured, the access bits are set to allow the group members to ac-
cess 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 inter-
faces.
NOTE:
If you change this and permissions have been dropped, you
must restart the server for the change to take effect.
Default: 8953
control-use-cert: <yes or no>
For localhost control-interface you can disable the use of TLS
by setting this option to "no". For local sockets, TLS is dis-
abled and the value of this option is ignored.
Default: yes
server-key-file: <private key file>
Path to the server private key. This file is generated by the
unbound-control-setup(8) utility. This file is used by the Un-
bound server, but not by unbound-control(8).
Default: unbound_server.key
server-cert-file: <certificate file.pem>
Path to the server self signed certificate. This file is gener-
ated by the unbound-control-setup(8) utility. This file is used
by the Unbound server, and also by unbound-control(8).
Default: unbound_server.pem
control-key-file: <private key file>
Path to the control client private key. This file is generated
by the unbound-control-setup(8) utility. This file is used by
unbound-control(8).
Default: unbound_control.key
control-cert-file: <certificate file.pem>
Path to the control client certificate. This certificate has to
be signed with the server certificate. This file is generated
by the unbound-control-setup(8) utility. This file is used by
unbound-control(8).
Default: unbound_control.pem
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 name-
servers is used. Class IN is assumed. The servers should be authority
servers, not recursors; Unbound performs the recursive processing it-
self 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 au-
thoritative 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 authorita-
tive 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 RFC 1918 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 non-default 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 IPv4 or IPv6.
To use a non-default 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-prime: <yes or 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 out-
dated, the resolver picks up a correct list online.
Default: no
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.
Default: no
stub-tls-upstream: <yes or no>
Enabled or disable whether the queries to this stub use TLS for
transport.
Default: 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: no
stub-no-cache: <yes or no>
If enabled, data inside the stub is not cached. This is useful
when you want immediate changes to be visible.
Default: no
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 recur-
sion 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 en-
try 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
zone.
forward-host: <domain name>
Name of server to forward to. Is itself resolved before it is
used.
To use a non-default 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 IPv4 or IPv6.
To use a non-default 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 op-
tion is enabled, Unbound will fall back to normal recursive res-
olution for this query as if no query forwarding had been speci-
fied.
Default: no
forward-tls-upstream: <yes or no>
Enabled or disable whether the queries to this forwarder use TLS
for transport. 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.
Default: no
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: no
forward-no-cache: <yes or no>
If enabled, data inside the forward is not cached. This is use-
ful when you want immediate changes to be visible.
Default: no
Authority Zone Options
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-ex-
clusive, configurable stages.
With for-downstream: yes (default), authority zones are processed after
local-zones and before cache. When used in this manner, Unbound re-
sponds 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 resolv-
ing.
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 an-
swer.
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 de-
tect 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 SERV-
FAIL, 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 non-default 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 depen-
dency on retrieving that IP address.
master: <IP address or host name>
Alternate syntax for primary.
url: <URL to zone file>
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 pri-
maries 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 or netblockIP/prefix>
With allow-notify you can specify additional sources of noti-
fies. 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.
NOTE:
The primaries from primary and url statements are allowed no-
tify by default.
fallback-enabled: <yes or no>
If enabled, Unbound falls back to querying the internet as a re-
solver for this zone when lookups fail. For example for DNSSEC
validation failures.
Default: no
for-downstream: <yes or no>
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: no and for-upstream: yes are set, then Un-
bound will DNSSEC validate the contents of the zone before serv-
ing the zone contents to clients and store validation results in
the cache.
Default: yes
for-upstream: <yes or no>
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 down-
stream clients, and use the zone data as a local copy to speed
up lookups.
Default: yes
zonemd-check: <yes or no>
Enable this option to check ZONEMD records in the zone. The
ZONEMD record is a checksum over the zone data. This includes
glue in the zone and data from the zone file, and excludes com-
ments from the zone file. When there is a DNSSEC chain of
trust, DNSSEC signatures are checked too.
Default: no
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 non-DNSSEC 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.
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.
Default: no
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, Un-
bound 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 attributes. Views can also contain
view-first, response-ip, response-ip-data and local-data-ptr attrib-
utes. View can be mapped to requests by specifying the view name in an
access-control-view attribute. Options from matching views will over-
ride 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>
Name of the view. Must be unique. This name is used in the
access-control-view attribute.
local-zone: <zone> <type>
View specific local zone elements. Has the same types and be-
haviour as the global local-zone elements. When there is at
least one local-zone: specified and view-first: no is set, the
default local-zones will be added to this view. Defaults can be
disabled using the nodefault type. When view-first: yes is set
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.
Default: 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 op-
tion (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 ab-
solute 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 mod-
ule 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 attribute. Multiple in-
stances of dynamic libraries are supported by adding the word dynlib
more than once.
The dynlib-file path should be specified as an absolute path relative
to the new path set by chroot, or as a relative path to the working di-
rectory.
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 directive,
e.g.:
module-config: "dns64 validator iterator"
and be compiled into the daemon to be enabled.
NOTE:
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.
Default: 64:ff9b::/96
dns64-synthall: <yes or no>
WARNING:
Debugging feature!
If enabled, synthesize all AAAA records despite the presence of
actual AAAA records.
Default: no
dns64-ignore-aaaa: <domain name>
List domain for which the AAAA records are ignored and the A
record is used by DNS64 processing instead. Can be entered mul-
tiple 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: sec-
tion:
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. The
prefix length must be one of /32, /40, /48, /56, /64 or /96.
Default: 64:ff9b::/96 (same as dns64-prefix)
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/pub-
lic keys cannot be generated by Unbound. You can use 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.
Default: no
dnscrypt-port: <port number>
On which port should dnscrypt should be activated.
NOTE:
There should be 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.
IMPORTANT:
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-key.
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. Like-
wise, it would allow one to prime the new cert/key without dis-
tributing the new cert yet, this can be useful when using a net-
work 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. 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 substan-
tial amount of CPU.
Default: 4m
dnscrypt-shared-secret-cache-slabs: <number>
Number of slabs in the dnscrypt shared secrets cache. Slabs re-
duce lock contention by threads. Must be set to a power of 2.
Setting (close) to the number of cpus is a fairly good setting.
If left unconfigured, it will be configured automatically to be
a power of 2 close to the number of configured threads in
multi-threaded environments.
Default: (unconfigured)
dnscrypt-nonce-cache-size: <memory size>
Give the size of the data structure in which the client nonces
are kept in. 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.
Default: 4m
dnscrypt-nonce-cache-slabs: <number>
Number of slabs in the dnscrypt nonce cache. Slabs reduce lock
contention by threads. Must be set to a power of 2. Setting
(close) to the number of cpus is a fairly good setting. If left
unconfigured, it will be configured automatically to be a power
of 2 close to the number of configured threads in multi-threaded
environments.
Default: (unconfigured)
EDNS Client Subnet Module Options
The ECS module must be configured in the module-config directive, e.g.:
module-config: "subnetcache validator iterator"
and be compiled into the daemon to be enabled.
NOTE:
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 in-
dicated 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, when
client-subnet-always-forward: yes is set. 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 dif-
ferent subnets are allowed to be stored for each address family. Ex-
ceeding that number, older entries will be purged from cache.
Note that due to the nature of how EDNS Client Subnet works, by segre-
gating the client IP space in order to try and have tailored responses
for prefixes of unknown sizes, resolution and cache response perfor-
mance are impacted as a result. Usage of the subnetcache module should
only be enabled in installations that require such functionality where
the resolver and the clients belong to different networks. An example
of that is an open resolver installation.
This module does not interact with the serve-expired* and prefetch op-
tions.
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. Au-
thorities 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>
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 en-
abled, the address check is skipped when the client query con-
tains an ECS record. And the lookup in the regular cache is
skipped.
Default: 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.
Default: 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.
Default: 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: 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. De-
fault: 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.
Default: 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.
Default: 100
Opportunistic IPsec Support Module Options
The IPsec module must be configured in the module-config directive,
e.g.:
module-config: "ipsecmod validator iterator"
and be compiled into Unbound by using --enable-ipsecmod to be enabled.
NOTE:
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 an-
swer was found, Unbound will call an external hook passing the follow-
ing 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: yes is set, 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.
Default: yes
ipsecmod-hook: <filename>
Specifies the external hook that Unbound will call with sys-
tem(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 suc-
cess value of 0. Failing to do so Unbound will reply with SERV-
FAIL. The A/AAAA answer will also not be cached.
Default: no
ipsecmod-max-ttl: <seconds>
Time to live maximum for A/AAAA cached records after calling the
external hook.
Default: 3600
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.
Default: no
ipsecmod-allow: <domain>
Allow the IPsec module 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: <domain>
Alternate syntax for ipsecmod-allow.
Cache DB Module Options
The Cache DB module must be configured in the module-config directive,
e.g.:
module-config: "validator cachedb iterator"
and be compiled into the daemon with --enable-cachedb.
If this module is enabled and configured, the specified backend data-
base 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.
If Unbound was built with --with-libhiredis on a system that has in-
stalled 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.
NOTE:
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-re-
cently-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 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 re-
connect 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 as-
sumption 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 con-
figuration, redis backend may also be used as described above.
Default: testframe
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 data-
base is shared by multiple Unbound instances, all instances must
use the same secret seed.
Default: "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.
Default: no
cachedb-check-when-serve-expired: <yes or no>
If enabled, the cachedb is checked before an expired response is
returned. When serve-expired is enabled, without
serve-expired-client-timeout , it then does not immediately re-
spond with an expired response from cache, but instead first
checks the cachedb for valid contents, and if so returns it. If
the cachedb also has no valid contents, the serve expired re-
sponse is sent. If also serve-expired-client-timeout is en-
abled, the expired response is delayed until the timeout ex-
pires. Unless the lookup succeeds within the timeout.
Default: yes
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 other-
wise Unbound will have to resolve the name of the server every
time it establishes a connection to the server.
Default: 127.0.0.1
redis-server-port: <port number>
The TCP port number of the Redis server.
Default: 6379
redis-server-path: <unix socket path>
The unix socket path to connect to the Redis server. Unix sock-
ets may have better throughput than the IP address option.
Default: "" (disabled)
redis-server-password: "<password>"
The Redis AUTH password to use for the Redis server. Only rele-
vant if Redis is configured for client password authorisation.
Default: "" (disabled)
redis-timeout: <msec>
The period until when Unbound waits for a response from the Re-
dis server. If this timeout expires Unbound closes the connec-
tion, treats it as if the Redis server does not have the re-
quested data, and will try to re-establish a new connection
later.
Default: 100
redis-command-timeout: <msec>
The timeout to use for Redis commands, in milliseconds. If 0,
it uses the redis-timeout value.
Default: 0
redis-connect-timeout: <msec>
The timeout to use for Redis connection set up, in milliseconds.
If 0, it uses the redis-timeout value.
Default: 0
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: 0, this option is inter-
nally reverted to "no".
NOTE:
Redis "SET ... EX" support is required for this option (Redis
>= 2.6.12).
Default: 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 per-
sisted in the same RDB/AOF file. If unsure about using this op-
tion, Redis documentation (https://redis.io/commands/select/)
suggests not to use a single Redis instance for multiple unre-
lated applications. The default database in Redis is 0 while
other logical databases need to be explicitly SELECT'ed upon
connecting.
Default: 0
redis-replica-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 other-
wise Unbound will have to resolve the name of the server every
time it establishes a connection to the server.
This server is treated as a read-only replica server (-
https://redis.io/docs/management/replica-
tion/#read-only-replica). If specified, all Redis read commands
will go to this replica server, while the write commands will go
to the redis-server-host.
Default: "" (disabled).
redis-replica-server-port: <port number>
The TCP port number of the Redis replica server.
Default: 6379
redis-replica-server-path: <unix socket path>
The unix socket path to connect to the Redis replica server.
Unix sockets may have better throughput than the IP address op-
tion.
Default: "" (disabled)
redis-replica-server-password: "<password>"
The Redis AUTH password to use for the Redis server. Only rele-
vant if Redis is configured for client password authorisation.
Default: "" (disabled)
redis-replica-timeout: <msec>
The period until when Unbound waits for a response from the Re-
dis replica server. 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.
Default: 100
redis-replica-command-timeout: <msec>
The timeout to use for Redis replica commands, in milliseconds.
If 0, it uses the redis-replica-timeout value.
Default: 0
redis-replica-connect-timeout: <msec>
The timeout to use for Redis replica connection set up, in mil-
liseconds. If 0, it uses the redis-replica-timeout value.
Default: 0
redis-replica-logical-db: <logical database index>
Same as redis-logical-db but for the Redis replica server.
Default: 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. 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.
Default: no
dnstap-bidirectional: <yes or no>
Use frame streams in bidirectional mode to transfer DNSTAP mes-
sages.
Default: yes
dnstap-socket-path: <file name>
Sets the unix socket file name for connecting to the server that
is listening on that socket.
Default:
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.
Default: ""
dnstap-tls: <yes or no>
Set this to use TLS to connect to the server specified in
dnstap-ip. If set to no, TCP is used to connect to the server.
Default: yes
dnstap-tls-server-name: <name of TLS authentication>
The TLS server name to authenticate the server with. Used when
dnstap-tls: yes is set. 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: ""
dnstap-tls-client-key-file: <file name>
The client key file for TLS client authentication. If "" client
authentication is not used.
Default: ""
dnstap-tls-client-cert-file: <file name>
The client cert file for TLS client authentication.
Default: ""
dnstap-send-identity: <yes or no>
If enabled, the server identity is included in the log messages.
Default: no
dnstap-send-version: <yes or no>
If enabled, the server version if included in the log messages.
Default: no
dnstap-identity: <string>
The identity to send with messages, if "" the hostname is used.
Default: ""
dnstap-version: <string>
The version to send with messages, if "" the package version is
used.
Default: ""
dnstap-sample-rate: <number>
The sample rate for log of messages, it logs only 1/N messages.
With 0 it is disabled. This is useful in a high volume environ-
ment, where log functionality would otherwise not be reliable.
For example 10 would spend only 1/10th time on logging, and 100
would only spend a hundredth of the time on logging.
Default: 0 (disabled)
dnstap-log-resolver-query-messages: <yes or no>
Enable to log resolver query messages. These are messages from
Unbound to upstream servers.
Default: no
dnstap-log-resolver-response-messages: <yes or no>
Enable to log resolver response messages. These are replies
from upstream servers to Unbound.
Default: no
dnstap-log-client-query-messages: <yes or no>
Enable to log client query messages. These are client queries
to Unbound.
Default: no
dnstap-log-client-response-messages: <yes or no>
Enable to log client response messages. These are responses
from Unbound to clients.
Default: no
dnstap-log-forwarder-query-messages: <yes or no>
Enable to log forwarder query messages.
Default: no
dnstap-log-forwarder-response-messages: <yes or no>
Enable to log forwarder response messages.
Default: no
Response Policy Zone Options
Response Policy Zones are configured with rpz:, and each one must have
a name attribute. There can be multiple ones, by listing multiple RPZ
clauses, each with a different name. RPZ clauses are applied in order
of configuration and any match from an earlier RPZ zone will terminate
the RPZ lookup. Note that a PASSTHRU action is still considered a
match. 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
any local-zone and before any auth-zone.
The RPZ zone is a regular DNS zone 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 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 non-default 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 depen-
dency 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 pri-
maries 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.
allow-notify: <IP address or host name or netblockIP/prefix>
With allow-notify you can specify additional sources of noti-
fies. 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.
NOTE:
The primaries from primary and url statements are allowed no-
tify 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, Un-
bound 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 actions 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: no
rpz-log-name: <name>
Specify a string to be part of the log line, for easy referenc-
ing.
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: 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: no
tags: "<list of tags>"
Limit the policies from this RPZ clause to clients with a match-
ing tag.
Tags need to be defined in define-tag and can be assigned to
client addresses using access-control-tag or interface-tag. En-
close 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 excep-
tional for the DNS. DNSSEC validation is enabled, just add trust an-
chors. 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 re-
ceive 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
Unbound log file. Default is to log to syslog(3).
SEE ALSO
unbound(8), unbound-checkonf(8).
AUTHOR
Unbound developers are mentioned in the CREDITS file in the distribu-
tion.
COPYRIGHT
1999-2025, NLnet Labs
1.24.0 Sep 18, 2025 UNBOUND.CONF(5)
