unbound.conf(5) unbound 1.20.0 unbound.conf(5)
NAME
unbound.conf - Unbound 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 ex-
tensive 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 number, level 0 means no verbosity, only errors.
Level 1 gives operational information. Level 2 gives detailed
operational information including short information per query.
Level 3 gives query level information, output per query. Level
4 gives algorithm level information. Level 5 logs client iden-
tification for cache misses. Default is level 1. The verbosity
can also be increased from the commandline, see unbound(8).
statistics-interval: <seconds>
The number of seconds between printing statistics to the log for
every thread. Disable with value 0 or "". Default is disabled.
The histogram statistics are only printed if replies were sent
during the statistics interval, requestlist statistics are
printed for every interval (but can be 0). This is because the
median calculation requires data to be present.
statistics-cumulative: <yes or no>
If enabled, statistics are cumulative since starting Unbound,
without clearing the statistics counters after logging the sta-
tistics. Default is no.
extended-statistics: <yes or no>
If enabled, extended statistics are printed from unbound-con-
trol(8). Default is off, because keeping track of more statis-
tics takes time. The counters are listed in unbound-control(8).
statistics-inhibit-zero: <yes or no>
If enabled, selected extended statistics with a value of 0 are
inhibited from printing with unbound-control(8). These are
query types, query classes, query opcodes, answer rcodes (except
NOERROR, FORMERR, SERVFAIL, NXDOMAIN, NOTIMPL, REFUSED) and RPZ
actions. Default is on.
num-threads: <number>
The number of threads to create to serve clients. Use 1 for no
threading.
port: <port number>
The port number, default 53, on which the server responds to
queries.
interface: <ip address or interface name [@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 to local-
host. If an interface name is used instead of an ip address,
the list of ip addresses on that interface are used. The inter-
faces are not changed on a reload (kill -HUP) but only on
restart. A port number can be specified with @port (without
spaces between interface and port number), if not specified the
default port (from port) is used.
ip-address: <ip address or interface name [@port]>
Same as interface: (for ease of compatibility with nsd.conf).
interface-automatic: <yes or no>
Listen on all addresses on all (current and future) interfaces,
detect the source interface on UDP queries and copy them to
replies. This is a lot like ip-transparent, but this option
services all interfaces whilst with ip-transparent you can se-
lect which (future) interfaces Unbound provides service on.
This feature is experimental, and needs support in your OS for
particular socket options. Default value is no.
interface-automatic-ports: <string>
List the port numbers that interface-automatic listens on. If
empty, the default port is listened on. The port numbers are
separated by spaces in the string. Default is "".
This can be used to have interface automatic to deal with the
interface, and listen on the normal port number, by including it
in the list, and also https or dns over tls port numbers by
putting them in the list as well.
outgoing-interface: <ip address or ip6 netblock>
Interface to use to connect to the network. This interface is
used to send queries to authoritative servers and receive their
replies. Can be given multiple times to work on several inter-
faces. If none are given the default (all) is used. You can
specify the same interfaces in interface: and outgoing-inter-
face: 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 pre-
fer-ip6: yes to increase the likelihood of IPv6 nameservers be-
ing selected for queries. On Linux you need these two commands
to be able to use the freebind socket option to receive traffic
for the ip6 netblock: ip -6 addr add mynetblock/64 dev lo && ip
-6 route add local mynetblock/64 dev lo
outgoing-range: <number>
Number of ports to open. This number of file descriptors can be
opened per thread. Must be at least 1. Default depends on com-
pile options. Larger numbers need extra resources from the oper-
ating system. For performance a very large value is best, use
libevent to make this possible.
outgoing-port-permit: <port number or range>
Permit Unbound to open this port or range of ports for use to
send queries. A larger number of permitted outgoing ports 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 IP4 and IP6. By default only ports
above 1024 that have not been assigned by IANA are used. Give a
port number or a range of the form "low-high", without spaces.
outgoing-num-tcp: <number>
Number of outgoing TCP buffers to allocate per thread. Default
is 10. If set to 0, or if do-tcp is "no", no TCP queries to au-
thoritative servers are done. For larger installations increas-
ing this value is a good idea.
incoming-num-tcp: <number>
Number of incoming TCP buffers to allocate per thread. Default
is 10. If set to 0, or if do-tcp is "no", no TCP queries from
clients are accepted. For larger installations increasing this
value is a good idea.
edns-buffer-size: <number>
Number of bytes size to advertise as the EDNS reassembly buffer
size. This is the value put into datagrams over UDP towards
peers. The actual buffer size is determined by msg-buffer-size
(both for TCP and UDP). Do not set higher than that value. De-
fault is 1232 which is the DNS Flag Day 2020 recommendation.
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 the outgoing tcp number).
max-udp-size: <number>
Maximum UDP response size (not applied to TCP response). 65536
disables the udp response size maximum, and uses the choice from
the client, always. Suggested values are 512 to 4096. Default
is 1232. The default value is the same as the default for
edns-buffer-size.
stream-wait-size: <number>
Number of bytes size maximum to use for waiting stream buffers.
Default is 4 megabytes. A plain number is in bytes, append 'k',
'm' or 'g' for kilobytes, megabytes or gigabytes (1024*1024
bytes in a megabyte). As TCP and TLS streams queue up multiple
results, the amount of memory used for these buffers does not
exceed this number, otherwise the responses are dropped. This
manages the total memory usage of the server (under heavy use),
the number of requests that can be queued up per connection is
also limited, with further requests waiting in TCP buffers.
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.
msg-cache-size: <number>
Number of bytes size of the message cache. Default is 4
megabytes. A plain number is in bytes, append 'k', 'm' or 'g'
for kilobytes, megabytes or gigabytes (1024*1024 bytes in a
megabyte).
msg-cache-slabs: <number>
Number of slabs in the message cache. Slabs reduce lock con-
tention by threads. Must be set to a power of 2. Setting
(close) to the number of cpus is a reasonable guess.
num-queries-per-thread: <number>
The number of queries that every thread will service 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, 512 or 1024.
jostle-timeout: <msec>
Timeout used when the server is very busy. Set to a value that
usually results in one roundtrip to the authority servers. If
too many queries arrive, then 50% of the queries are allowed to
run to completion, and the other 50% are replaced with the new
incoming query if they have already spent more than their al-
lowed time. This protects against denial of service by slow
queries or high query rates. Default 200 milliseconds. The ef-
fect is that the qps for long-lasting queries is about (num-
queriesperthread / 2) / (average time for such long queries)
qps. The qps for short queries can be about (numqueries-
perthread / 2) / (jostletimeout in whole seconds) qps per
thread, about (1024/2)*5 = 2560 qps by default.
delay-close: <msec>
Extra delay for timeouted UDP ports before they are closed, in
msec. Default is 0, and that disables it. This prevents very
delayed answer packets from the upstream (recursive) servers
from bouncing against closed ports and setting off all sort of
close-port counters, with eg. 1500 msec. When timeouts happen
you need extra sockets, it checks the ID and remote IP of pack-
ets, and unwanted packets are added to the unwanted packet
counter.
udp-connect: <yes or no>
Perform connect for UDP sockets that mitigates ICMP side channel
leakage. Default is yes.
unknown-server-time-limit: <msec>
The wait time in msec for waiting for an unknown server to 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 is 376 msec.
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 re-
ceive 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 dis-
ables it. Default 1900 msec.
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 is 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, the limit can be higher.
Default is 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.
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.
so-rcvbuf: <number>
If not 0, then set the SO_RCVBUF socket option to get more buf-
fer space on UDP port 53 incoming queries. So that short spikes
on busy servers do not drop packets (see counter in netstat
-su). Default is 0 (use system value). Otherwise, the number
of bytes to ask for, try "4m" on a busy server. The OS caps it
at a maximum, on linux Unbound needs root permission to bypass
the limit, or the admin can use sysctl net.core.rmem_max. On
BSD change kern.ipc.maxsockbuf in /etc/sysctl.conf. On OpenBSD
change header and recompile kernel. On Solaris ndd -set /dev/udp
udp_max_buf 8388608.
so-sndbuf: <number>
If not 0, then set the SO_SNDBUF socket option to get more buf-
fer space on UDP port 53 outgoing queries. This for very busy
servers handles spikes in answer traffic, otherwise 'send: re-
source temporarily unavailable' can get logged, the buffer over-
run is also visible by netstat -su. Default is 0 (use system
value). Specify the number of bytes to ask for, try "4m" on a
very busy server. The OS caps it at a maximum, on linux Unbound
needs root permission to bypass the limit, or the admin can use
sysctl net.core.wmem_max. On BSD, Solaris changes are similar
to so-rcvbuf.
so-reuseport: <yes or no>
If yes, then open dedicated listening sockets for incoming
queries for each thread and try to set the SO_REUSEPORT socket
option on each socket. May distribute incoming queries to
threads more evenly. Default is yes. On Linux it is supported
in kernels >= 3.9. On other systems, FreeBSD, OSX it may also
work. You can enable it (on any platform and kernel), it then
attempts to open the port and passes the option if it was avail-
able at compile time, if that works it is used, if it fails, it
continues silently (unless verbosity 3) without the option. At
extreme load it could be better to turn it off to distribute the
queries evenly, reported for Linux systems (4.4.x).
ip-transparent: <yes or no>
If yes, then use IP_TRANSPARENT socket option on sockets where
Unbound is listening for incoming traffic. Default no. Allows
you to bind to non-local interfaces. For example for non-exis-
tent IP addresses that are going to exist later on, with host
failover configuration. This is a lot like interface-automatic,
but that one services all interfaces and with this option you
can select which (future) interfaces Unbound provides service
on. This option needs Unbound to be started with root permis-
sions on some systems. The option uses IP_BINDANY on FreeBSD
systems and SO_BINDANY on OpenBSD systems.
ip-freebind: <yes or no>
If yes, then use IP_FREEBIND socket option on sockets where Un-
bound is listening to incoming traffic. Default no. Allows you
to bind to IP addresses that are nonlocal or do not exist, like
when the network interface or IP address is down. Exists only
on Linux, where the similar ip-transparent option is also avail-
able.
ip-dscp: <number>
The value of the Differentiated Services Codepoint (DSCP) in the
differentiated services field (DS) of the outgoing IP packet
headers. The field replaces the outdated IPv4 Type-Of-Service
field and the IPv6 traffic class field.
rrset-cache-size: <number>
Number of bytes size of the RRset cache. Default is 4 megabytes.
A plain number is in bytes, append 'k', 'm' or 'g' for kilo-
bytes, megabytes or gigabytes (1024*1024 bytes in a megabyte).
rrset-cache-slabs: <number>
Number of slabs in the RRset cache. Slabs reduce lock contention
by threads. Must be set to a power of 2.
cache-max-ttl: <seconds>
Time to live maximum for RRsets and messages in the cache. De-
fault is 86400 seconds (1 day). When the TTL expires, the cache
item has expired. Can be set lower to force the resolver to
query for data often, and not trust (very large) TTL values.
Downstream clients also see the lower TTL.
cache-min-ttl: <seconds>
Time to live minimum for RRsets and messages in the cache. De-
fault is 0. If the minimum kicks in, the data is cached for
longer than the domain owner intended, and thus less queries are
made to look up the data. Zero makes sure the data in the cache
is as the domain owner intended, higher values, especially more
than an hour or so, can lead to trouble as the data in the cache
does not match up with the actual data any more.
cache-max-negative-ttl: <seconds>
Time to live maximum for negative responses, these have a SOA in
the authority section that is limited in time. Default is 3600.
This applies to nxdomain and nodata answers.
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. Default is 0
(disabled). If this is disabled and cache-min-ttl is config-
ured, it will take effect instead. In that case you can set
this to 1 to honor the upstream TTL. This applies to nxdomain
and nodata answers.
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 is 900.
infra-cache-slabs: <number>
Number of slabs in the infrastructure cache. Slabs reduce lock
contention by threads. Must be set to a power of 2.
infra-cache-numhosts: <number>
Number of hosts for which information is cached. Default is
10000.
infra-cache-min-rtt: <msec>
Lower limit for dynamic retransmit timeout calculation in infra-
structure cache. Default is 50 milliseconds. Increase this value
if using forwarders needing more time to do recursive name reso-
lution.
infra-cache-max-rtt: <msec>
Upper limit for dynamic retransmit timeout calculation in infra-
structure cache. Default is 2 minutes.
infra-keep-probing: <yes or no>
If enabled the server keeps probing hosts that are down, in the
one probe at a time regime. Default is no. Hosts that are
down, eg. they did not respond during the one probe at a time
period, are marked as down and it may take infra-host-ttl time
to get probed again.
define-tag: <"list of tags">
Define the tags that can be used with local-zone and access-con-
trol. Enclose the list between quotes ("") and put spaces be-
tween tags.
do-ip4: <yes or no>
Enable or disable whether ip4 queries are answered or issued.
Default is yes.
do-ip6: <yes or no>
Enable or disable whether ip6 queries are answered or issued.
Default is yes. If disabled, queries are not answered on IPv6,
and queries are not sent on IPv6 to the internet nameservers.
With this option you can disable the IPv6 transport for sending
DNS traffic, it does not impact the contents of the DNS traffic,
which may have ip4 and ip6 addresses in it.
prefer-ip4: <yes or no>
If enabled, prefer IPv4 transport for sending DNS queries to in-
ternet nameservers. Default is no. Useful if the IPv6 netblock
the server has, the entire /64 of that is not owned by one oper-
ator and the reputation of the netblock /64 is an issue, using
IPv4 then uses the IPv4 filters that the upstream servers have.
prefer-ip6: <yes or no>
If enabled, prefer IPv6 transport for sending DNS queries to in-
ternet nameservers. Default is no.
do-udp: <yes or no>
Enable or disable whether UDP queries are answered or issued.
Default is yes.
do-tcp: <yes or no>
Enable or disable whether TCP queries are answered or issued.
Default is yes.
tcp-mss: <number>
Maximum segment size (MSS) of TCP socket on which the server 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). De-
fault is system default MSS determined by interface MTU and ne-
gotiation 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. This op-
tion defaults to 30000 milliseconds. When the number of free
incoming TCP buffers falls below 50% of the total number config-
ured, the option value used is progressively reduced, first to
1% of the configured value, then to 0.2% of the configured value
if the number of free buffers falls below 35% of the total num-
ber configured, and finally to 0 if the number of free buffers
falls below 20% of the total number configured. A minimum time-
out of 200 milliseconds is observed regardless of the option
value used. It will be overriden by edns-tcp-keepalive-timeout
if edns-tcp-keepalive is enabled.
tcp-reuse-timeout: <msec>
The period Unbound will keep TCP persistent connections open to
authority servers. This option defaults to 60000 milliseconds.
max-reuse-tcp-queries: <number>
The maximum number of queries that can be sent on a persistent
TCP connection. This option defaults to 200 queries.
tcp-auth-query-timeout: <number>
Timeout in milliseconds for TCP queries to auth servers. This
option defaults to 3000 milliseconds.
edns-tcp-keepalive: <yes or no>
Enable or disable EDNS TCP Keepalive. Default is no.
edns-tcp-keepalive-timeout: <msec>
Overrides tcp-idle-timeout when edns-tcp-keepalive is enabled.
If the client supports the EDNS TCP Keepalive option, Unbound
sends the timeout value to the client to encourage it to close
the connection before the server times out. This option de-
faults to 120000 milliseconds.
sock-queue-timeout: <sec>
UDP queries that have waited in the socket buffer for a long
time can be dropped. Default is 0, disabled. The time is set in
seconds, 3 could be a good value to ignore old queries that
likely the client does not need a reply for any more. This could
happen if the host has not been able to service the queries for
a while, i.e. Unbound is not running, and then is enabled again.
It uses timestamp socket options.
tcp-upstream: <yes or no>
Enable or disable whether the upstream queries use TCP only for
transport. Default is no. Useful in tunneling scenarios. If
set to no you can specify TCP transport only for selected for-
ward or stub zones using forward-tcp-upstream or stub-tcp-up-
stream respectively.
udp-upstream-without-downstream: <yes or no>
Enable udp upstream even if do-udp is no. Default is no, and
this does not change anything. Useful for TLS service
providers, that want no udp downstream but use udp to fetch data
upstream.
tls-upstream: <yes or no>
Enabled or disable whether the upstream queries use TLS only for
transport. Default is no. Useful in tunneling scenarios. The
TLS contains plain DNS in TCP wireformat. The other server must
support this (see tls-service-key). If you enable this, also
configure a tls-cert-bundle or use tls-win-cert or tls-sys-
tem-cert to load CA certs, otherwise the connections cannot be
authenticated. This option enables TLS for all of them, but if
you do not set this you can configure TLS specifically for some
forward zones with forward-tls-upstream. And also with
stub-tls-upstream.
ssl-upstream: <yes or no>
Alternate syntax for tls-upstream. If both are present in the
config file the last is used.
tls-service-key: <file>
If enabled, the server provides DNS-over-TLS or DNS-over-HTTPS
service on the TCP ports marked implicitly or explicitly for
these services with tls-port or https-port. The file must 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. The default is "", turned off.
Enabling or disabling this service requires a restart (a reload
is not enough), because the key is read while root permissions
are held and before chroot (if any). The ports enabled implic-
itly or explicitly via tls-port: and https-port: do not provide
normal DNS TCP service. Unbound needs to be compiled with lib-
nghttp2 in order to provide DNS-over-HTTPS.
ssl-service-key: <file>
Alternate syntax for tls-service-key.
tls-service-pem: <file>
The public key certificate pem file for the tls service. De-
fault is "", turned off.
ssl-service-pem: <file>
Alternate syntax for tls-service-pem.
tls-port: <number>
The port number on which to provide TCP TLS service, default
853, only interfaces configured with that port number as @number
get the TLS service.
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 permission drop
and chroot.
ssl-cert-bundle: <file>
Alternate syntax for tls-cert-bundle.
tls-win-cert: <yes or no>
Add the system certificates to the cert bundle certificates for
authentication. If no cert bundle, it uses only these certifi-
cates. Default is no. On windows this option uses the certifi-
cates from the cert store. Use the tls-cert-bundle option on
other systems. On other systems, this option enables the system
certificates.
tls-system-cert: <yes or no>
This the same setting as the tls-win-cert setting, under a dif-
ferent name. Because it is not windows specific.
tls-additional-port: <portnr>
List portnumbers as tls-additional-port, and when interfaces are
defined, eg. with the @port suffix, as this port number, they
provide dns over TLS service. Can list multiple, each on a new
statement.
tls-session-ticket-keys: <file>
If not "", lists files with 80 bytes of random contents that are
used to perform TLS session resumption for clients using the 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 cre-
ate a second key, that is the name used to identify the key.
Then there is 32 bytes random data for an AES key and then 32
bytes random data for the HMAC key.
tls-ciphers: <string with cipher list>
Set the list of ciphers to allow when serving TLS. Use "" for
defaults, and that is the default.
tls-ciphersuites: <string with ciphersuites list>
Set the list of ciphersuites to allow when serving TLS. This is
for newer TLS 1.3 connections. Use "" for defaults, and that is
the default.
pad-responses: <yes or no>
If enabled, TLS serviced queries that contained an EDNS Padding
option will cause responses padded to the closest multiple of
the size specified in pad-responses-block-size. Default is yes.
pad-responses-block-size: <number>
The block size with which to pad responses serviced over TLS.
Only responses to padded queries will be padded. Default is
468.
pad-queries: <yes or no>
If enabled, all queries sent over TLS upstreams will be padded
to the closest multiple of the size specified in
pad-queries-block-size. Default is yes.
pad-queries-block-size: <number>
The block size with which to pad queries sent over TLS up-
streams. Default is 128.
tls-use-sni: <yes or no>
Enable or disable sending the SNI extension on TLS connections.
Default is yes. Changing the value requires a reload.
https-port: <number>
The port number on which to provide DNS-over-HTTPS service, de-
fault 443, only interfaces configured with that port number as
@number get the HTTPS service.
http-endpoint: <endpoint string>
The HTTP endpoint to provide DNS-over-HTTPS service on. Default
"/dns-query".
http-max-streams: <number of streams>
Number used in the SETTINGS_MAX_CONCURRENT_STREAMS parameter in
the HTTP/2 SETTINGS frame for DNS-over-HTTPS connections. De-
fault 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. Default is 4 megabytes. A plain
number is in bytes, append 'k', 'm' or 'g' for kilobytes,
megabytes or gigabytes (1024*1024 bytes in a megabyte).
http-response-buffer-size: <size in bytes>
Maximum number of bytes used for all HTTP/2 response buffers
combined. These buffers contain DNS responses waiting to be
written back to the clients. An RST_STREAM frame will be send
to streams exceeding this limit. Default is 4 megabytes. A plain
number is in bytes, append 'k', 'm' or 'g' for kilobytes,
megabytes or gigabytes (1024*1024 bytes in a megabyte).
http-nodelay: <yes or no>
Set TCP_NODELAY socket option on sockets used to provide DNS-
over-HTTPS service. Ignored if the option is not available. De-
fault is yes.
http-notls-downstream: <yes or no>
Disable use of TLS for the downstream DNS-over-HTTP connections.
Useful for local back end servers. Default is no.
proxy-protocol-port: <portnr>
List port numbers as proxy-protocol-port, and when interfaces
are defined, eg. with the @port suffix, as this port number,
they support and expect PROXYv2. In this case the proxy address
will only be used for the network communication and initial ACL
(check if the proxy itself is denied/refused by configuration).
The proxied address (if any) will then be used as the true
client address and will be used where applicable for logging,
ACL, DNSTAP, RPZ and IP ratelimiting. PROXYv2 is supported for
UDP and TCP/TLS listening interfaces. There is no support for
PROXYv2 on a DoH or DNSCrypt listening interface. Can list mul-
tiple, each on a new statement.
use-systemd: <yes or no>
Enable or disable systemd socket activation. Default is no.
do-daemonize: <yes or no>
Enable or disable whether the Unbound server forks into the
background as a daemon. Set the value to no when Unbound runs
as systemd service. Default is yes.
tcp-connection-limit: <IP netblock> <limit>
Allow up to limit simultaneous TCP connections from the given
netblock. When at the limit, further connections are accepted
but closed immediately. This option is experimental at this
time.
access-control: <IP netblock> <action>
Specify treatment of incoming queries from their originating IP
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 IP4 or IP6 address with /size ap-
pended for a classless network block. The action can be deny,
refuse, allow, allow_setrd, allow_snoop, allow_cookie,
deny_non_local or refuse_non_local. The most specific netblock
match is used, if none match refuse is used. The order of the
access-control statements therefore does not matter.
The deny action stops queries from hosts from that netblock.
The refuse action stops queries too, but sends a DNS rcode RE-
FUSED error message back.
The allow action gives access to clients from that netblock. It
gives only access for recursion clients (which is what almost
all clients need). Nonrecursive queries are refused.
The allow action does allow nonrecursive queries to access the
local-data that is configured. The reason is that this does not
involve the Unbound server recursive lookup algorithm, and
static data is served in the reply. This supports normal opera-
tions where nonrecursive queries are made for the authoritative
data. For nonrecursive queries any replies from the dynamic
cache are refused.
The allow_setrd action ignores the recursion desired (RD) bit
and treats all requests as if the recursion desired bit is set.
Note that this behavior violates RFC 1034 which states that a
name server should never perform recursive service unless asked
via the RD bit since this interferes with trouble shooting of
name servers and their databases. This prohibited behavior may
be useful if another DNS server must forward requests for spe-
cific zones to a resolver DNS server, but only supports stub do-
mains and sends queries to the resolver DNS server with the RD
bit cleared.
The allow_snoop action gives nonrecursive access too. This give
both recursive and non recursive access. The name allow_snoop
refers to cache snooping, a technique to use nonrecursive
queries to examine the cache contents (for malicious acts).
However, nonrecursive queries can also be a valuable debugging
tool (when you want to examine the cache contents). In that case
use allow_snoop for your administration host.
The allow_cookie action allows access only to UDP queries that
contain a valid DNS Cookie as specified in RFC 7873 and RFC
9018, when the answer-cookie option is enabled. UDP queries
containing only a DNS Client Cookie and no Server Cookie, or an
invalid DNS Cookie, will receive a BADCOOKIE response including
a newly generated DNS Cookie, allowing clients to retry with
that DNS Cookie. The allow_cookie action will also accept re-
quests over stateful transports, regardless of the presence of
an DNS Cookie and regardless of the answer-cookie setting. UDP
queries without a DNS Cookie receive REFUSED responses with the
TC flag set, that may trigger fall back to TCP for those
clients.
By default only localhost is allowed, the rest is refused. The
default is refused, because that is protocol-friendly. The DNS
protocol is not designed to handle dropped packets due to pol-
icy, and dropping may result in (possibly excessive) retried
queries.
The deny_non_local and refuse_non_local settings are for hosts
that are only allowed to query for the authoritative local-data,
they are not allowed full recursion but only the static data.
With deny_non_local, messages that are disallowed are dropped,
with refuse_non_local they receive error code REFUSED.
access-control-tag: <IP netblock> <"list of tags">
Assign tags to access-control elements. Clients using this ac-
cess control element use localzones that are tagged with one of
these tags. Tags must be defined in define-tags. Enclose list
of tags in quotes ("") and put spaces between tags. If ac-
cess-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 lo-
cal-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-con-
trol:. Interfaces are refused by default. By default only lo-
calhost (the IP netblock, not the loopback interface) is allowed
through the default access-control: behavior.
Note that the interface needs to be already specified with in-
terface: and that any access-control*: setting overrides all in-
terface-*: settings for targeted clients.
interface-tag: <ip address or interface name [@port]> <"list of tags">
Similar to access-control-tag: but for interfaces.
Note that the interface needs to be already specified with in-
terface: and that any access-control*: setting overrides all in-
terface-*: settings 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 that the interface needs to be already specified with in-
terface: and that any access-control*: setting overrides all in-
terface-*: settings 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 that the interface needs to be already specified with in-
terface: and that any access-control*: setting overrides all in-
terface-*: settings for targeted clients.
interface-view: <ip address or interface name [@port]> <view name>
Similar to access-control-view: but for interfaces.
Note that the interface needs to be already specified with in-
terface: and that any access-control*: setting overrides all in-
terface-*: settings for targeted clients.
chroot: <directory>
If chroot is enabled, you should pass the configfile (from the
commandline) as a full path from the original root. After the
chroot has been performed the now defunct portion of the config
file path is removed to be able to reread the config after a
reload.
All other file paths (working dir, logfile, roothints, and key
files) can be specified in several ways: as an absolute path
relative to the new root, as a relative path to the working 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 is done to the given directory. By default ch-
root is enabled and the default is "/usr/local/etc/unbound". If
you give "" no chroot is performed.
username: <name>
If given, after binding the port the user privileges are
dropped. Default is "unbound". If you give username: "" no user
change is performed.
If this user is not capable of binding the port, reloads (by
signal HUP) will still retain the opened ports. If you change
the port number in the config file, and that new port number re-
quires privileges, then a reload will fail; a restart is needed.
directory: <directory>
Sets the working directory for the program. Default is "/usr/lo-
cal/etc/unbound". On Windows the string "%EXECUTABLE%" tries to
change to the directory that unbound.exe resides in. If you
give a server: directory: dir before include: file statements
then those includes can be relative to the working directory.
logfile: <filename>
If "" is given, logging goes to stderr, or nowhere once 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 is option is set to
"no". The logfile is reopened (for append) when the config file
is reread, on SIGHUP.
use-syslog: <yes or no>
Sets Unbound to send log messages to the syslogd, using sys-
log(3). The log facility LOG_DAEMON is used, with identity "un-
bound". The logfile setting is overridden when use-syslog is
turned on. The default is to log to syslog.
log-identity: <string>
If "" is given (default), then the name of the executable, usu-
ally "unbound" is used to report to the log. Enter a string to
override it with that, which is useful on systems that run more
than one instance of Unbound, with different configurations, so
that the logs can be easily distinguished against.
log-time-ascii: <yes or no>
Sets logfile lines to use a timestamp in UTC ascii. Default is
no, which prints the seconds since 1970 in brackets. No effect
if using syslog, in that case syslog formats the timestamp
printed into the log files.
log-queries: <yes or no>
Prints one line per query to the log, with the log timestamp and
IP address, name, type and class. Default is no. Note that it
takes time to print these lines which makes the server (signifi-
cantly) slower. Odd (nonprintable) characters in names are
printed as '?'.
log-replies: <yes or no>
Prints one line per reply to the log, with the log timestamp and
IP address, name, type, class, return code, time to resolve,
from cache and response size. Default is no. Note that it
takes time to print these lines which makes the server (signifi-
cantly) slower. Odd (nonprintable) characters in names are
printed as '?'.
log-tag-queryreply: <yes or no>
Prints the word 'query' and 'reply' with log-queries and
log-replies. This makes filtering logs easier. The default is
off (for backwards compatibility).
log-destaddr: <yes or no>
Prints the destination address, port and type in the log-replies
output. This disambiguates what type of traffic, eg. udp or
tcp, and to what local port the traffic was sent to.
log-local-actions: <yes or no>
Print log lines to inform about local zone actions. These lines
are like the local-zone type inform prints out, but they are
also printed for the other types of local zones.
log-servfail: <yes or no>
Print log lines that say why queries return SERVFAIL to clients.
This is separate from the verbosity debug logs, much smaller,
and printed at the error level, not the info level of debug info
from verbosity.
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.
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.
hide-identity: <yes or no>
If enabled id.server and hostname.bind queries are refused.
identity: <string>
Set the identity to report. If set to "", the default, then the
hostname of the server is returned.
hide-version: <yes or no>
If enabled version.server and version.bind queries are refused.
version: <string>
Set the version to report. If set to "", the default, then the
package version is returned.
hide-http-user-agent: <yes or no>
If enabled the HTTP header User-Agent is not set. Use with 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.
http-user-agent: <string>
Set the HTTP User-Agent header for outgoing HTTP requests. If
set to "", the default, then the package name and version are
used.
nsid: <string>
Add the specified nsid to the EDNS section of the answer when
queried with an NSID EDNS enabled packet. As a sequence of hex
characters or with ascii_ prefix and then an ascii string.
hide-trustanchor: <yes or no>
If enabled trustanchor.unbound queries are refused.
target-fetch-policy: <"list of numbers">
Set the target fetch policy used by Unbound to determine if it
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. The default is "3 2 1 0 0". Setting all zeroes, "0 0 0 0
0" gives behaviour closer to that of BIND 9, while setting "-1
-1 -1 -1 -1" gives behaviour rumoured to be closer to that of
BIND 8.
harden-short-bufsize: <yes or no>
Very small EDNS buffer sizes from queries are ignored. Default
is on, as described in the standard.
harden-large-queries: <yes or no>
Very large queries are ignored. Default is off, since it is le-
gal protocol wise to send these, and could be necessary for op-
eration if TSIG or EDNS payload is very large.
harden-glue: <yes or no>
Will trust glue only if it is within the servers authority. De-
fault is yes.
harden-dnssec-stripped: <yes or no>
Require DNSSEC data for trust-anchored zones, if such data is
absent, the zone becomes bogus. If turned off, and no DNSSEC
data is received (or the DNSKEY data fails to validate), then
the zone is made insecure, this behaves like there is no trust
anchor. You could turn this off if you are sometimes behind an
intrusive firewall (of some sort) that removes DNSSEC data from
packets, or a zone changes from signed to unsigned to badly
signed often. If turned off you run the risk of a downgrade at-
tack that disables security for a zone. Default is yes.
harden-below-nxdomain: <yes or no>
From RFC 8020 (with title "NXDOMAIN: There Really Is Nothing 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. Default is yes. The nxdomain must be secure, this
means nsec3 with optout is insufficient.
harden-referral-path: <yes or no>
Harden the referral path by performing additional queries for
infrastructure data. Validates the replies if trust anchors are
configured and the zones are signed. This enforces DNSSEC vali-
dation on nameserver NS sets and the nameserver addresses that
are encountered on the referral path to the answer. Default no,
because it burdens the authority servers, and it is not RFC
standard, and could lead to performance problems because of the
extra query load that is generated. Experimental option. If
you enable it consider adding more numbers after the tar-
get-fetch-policy to increase the max depth that is checked to.
harden-algo-downgrade: <yes or no>
Harden against algorithm downgrade when multiple algorithms are
advertised in the DS record. If no, allows the weakest algo-
rithm to validate the zone. Default is no. Zone signers must
produce zones that allow this feature to work, but sometimes
they do not, and turning this option off avoids that validation
failure.
harden-unknown-additional: <yes or no>
Harden against unknown records in the authority section and ad-
ditional section. Default is no. If no, such records are copied
from the upstream and presented to the client together with the
answer. If yes, it could hamper future protocol developments
that want to add records.
use-caps-for-id: <yes or no>
Use 0x20-encoded random bits in the query to foil spoof 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. Disabled by default. This feature is
an experimental implementation of draft dns-0x20.
caps-exempt: <domain>
Exempt the domain so that it does not receive caps-for-id 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: <yes or no>
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 is yes.
qname-minimisation-strict: <yes or no>
QNAME minimisation in strict mode. Do not fall-back to sending
full QNAME to potentially broken nameservers. A lot of domains
will not be resolvable when this option in enabled. Only use if
you know what you are doing. This option only has effect when
qname-minimisation is enabled. Default is no.
aggressive-nsec: <yes or no>
Aggressive NSEC uses the DNSSEC NSEC chain to synthesize NXDO-
MAIN and other denials, using information from previous NXDO-
MAINs answers. Default is yes. It helps to reduce the query
rate towards targets that get a very high nonexistent name
lookup rate.
private-address: <IP address or subnet>
Give IPv4 of IPv6 addresses or classless subnets. These are 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 addi-
tional names using private-domain. No private addresses are en-
abled by default. We consider to enable this for the RFC1918
private IP address space by default in later releases. That
would enable private addresses for 10.0.0.0/8 172.16.0.0/12
192.168.0.0/16 169.254.0.0/16 fd00::/8 and fe80::/10, since the
RFC standards say these addresses should not be visible on the
public internet. Turning on 127.0.0.0/8 would hinder many spam-
blocklists 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 is none.
unwanted-reply-threshold: <number>
If set, a total number of unwanted replies is kept track of in
every thread. When it reaches the threshold, a defensive action
is taken and a warning is printed to the log. The defensive ac-
tion is to clear the rrset and message caches, hopefully flush-
ing away any poison. A value of 10 million is suggested. De-
fault is 0 (turned off).
do-not-query-address: <IP address>
Do not query the given IP address. Can be IP4 or IP6. Append
/num to indicate a classless delegation netblock, for example
like 10.2.3.4/24 or 2001::11/64.
do-not-query-localhost: <yes or no>
If yes, localhost is added to the do-not-query-address entries,
both IP6 ::1 and IP4 127.0.0.1/8. If no, then localhost can be
used to send queries to. Default is yes.
prefetch: <yes or no>
If yes, message cache elements are prefetched before they expire
to keep the cache up to date. Default is no. Turning it on
gives about 10 percent more traffic and load on the machine, but
popular items do not expire from the cache.
prefetch-key: <yes or no>
If yes, fetch the DNSKEYs earlier in the validation process,
when a DS record is encountered. This lowers the latency of re-
quests. It does use a little more CPU. Also if the cache is
set to 0, it is no use. Default is no.
deny-any: <yes or no>
If yes, deny queries of type ANY with an empty response. De-
fault is no. If disabled, Unbound responds with a short list of
resource records if some can be found in the cache and makes the
upstream type ANY query if there are none.
rrset-roundrobin: <yes or no>
If yes, Unbound rotates RRSet order in response (the random num-
ber is taken from the query ID, for speed and thread safety).
Default is yes.
minimal-responses: <yes or no>
If yes, Unbound does not insert authority/additional sections
into response messages when those sections are not required.
This reduces response size significantly, and may avoid TCP
fallback for some responses. This may cause a slight speedup.
The default is yes, even though the DNS protocol RFCs mandate
these sections, and the additional content could be of use and
save roundtrips for clients. Because they are not used, and the
saved roundtrips are easier saved with prefetch, whilst this is
faster.
disable-dnssec-lame-check: <yes or no>
If true, disables the DNSSEC lameness check in the iterator.
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.
module-config: <"module names">
Module configuration, a list of module names separated by spa-
ces, surround the string with quotes (""). The modules can be
respip, validator, or iterator (and possibly more, see below).
Setting this to just "iterator" will result in a non-validating
server. Setting this to "validator iterator" will turn on
DNSSEC validation. The ordering of the modules is significant,
the order decides the order of processing. You must also set
trust-anchors for validation to be useful. Adding respip to the
front will cause RPZ processing to be done on all queries. The
default is "validator iterator".
When the server is built with EDNS client subnet support the de-
fault is "subnetcache validator iterator". Most modules that
need to be listed here have to be listed at the beginning of the
line. The subnetcachedb module has to be listed just before the
iterator. The python module can be listed in different places,
it then processes the output of the module it is just before.
The dynlib module can be listed pretty much anywhere, it is only
a very thin wrapper that allows dynamic libraries to run in its
place.
trust-anchor-file: <filename>
File with trusted keys for validation. Both DS and DNSKEY en-
tries can appear in the file. The format of the file is the
standard DNS Zone file format. Default is "", or no trust an-
chor file.
auto-trust-anchor-file: <filename>
File with trust anchor for one zone, which is tracked with
RFC5011 probes. The probes are run several times per month,
thus the machine must be online frequently. The initial file
can be one with contents as described in trust-anchor-file. The
file is written to when the anchor is updated, so the Unbound
user must have write permission. Write permission to the file,
but also to the directory it is in (to create a temporary file,
which is necessary to deal with filesystem full events), it must
also be inside the chroot (if that is used).
trust-anchor: <"Resource Record">
A DS or DNSKEY RR for a key to use for validation. Multiple en-
tries can be given to specify multiple trusted keys, in addition
to the trust-anchor-files. The resource record is entered in
the same format as 'dig' or 'drill' prints them, the 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 ig-
nored. A class can be specified, but class IN is default.
trusted-keys-file: <filename>
File with trusted keys for validation. Specify more than one
file with several entries, one file per entry. Like trust-an-
chor-file but has a different file format. Format is BIND-9
style format, the trusted-keys { name flag proto algo "key"; };
clauses are read. It is possible to use wildcards with this
statement, the wildcard is expanded on start and on reload.
trust-anchor-signaling: <yes or no>
Send RFC8145 key tag query after trust anchor priming. Default
is yes.
root-key-sentinel: <yes or no>
Root key trust anchor sentinel. Default is yes.
domain-insecure: <domain name>
Sets domain name to be insecure, DNSSEC chain of trust is ig-
nored towards the domain name. So a trust anchor above the do-
main name can not make the domain secure with a DS record, such
a DS record is then ignored. Can be given multiple times to
specify multiple domains that are treated as if unsigned. If
you set trust anchors for the domain they override this setting
(and the domain is secured).
This can be useful if you want to make sure a trust anchor for
external lookups does not affect an (unsigned) internal domain.
A DS record externally can create validation failures for that
internal domain.
val-override-date: <rrsig-style date spec>
Default is "" or "0", which disables this debugging feature. If
enabled by giving a RRSIG style date, that date is used for ver-
ifying RRSIG inception and expiration dates, instead of the cur-
rent date. Do not set this unless you are debugging signature
inception and expiration. The value -1 ignores the date alto-
gether, useful for some special applications.
val-sig-skew-min: <seconds>
Minimum number of seconds of clock skew to apply to validated
signatures. A value of 10% of the signature lifetime (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.
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.
val-max-restart: <number>
The maximum number the validator should restart validation with
another authority in case of failed validation. Default is 5.
val-bogus-ttl: <number>
The time to live for bogus data. This is data that has failed
validation; due to invalid signatures or other checks. The TTL
from that data cannot be trusted, and this value is used in-
stead. The value is in seconds, default 60. The time interval
prevents repeated revalidation of bogus data.
val-clean-additional: <yes or no>
Instruct the validator to remove data from the additional sec-
tion of secure messages that are not signed properly. Messages
that are insecure, bogus, indeterminate or unchecked are not af-
fected. Default is yes. Use this setting to protect the users
that rely on this validator for authentication from potentially
bad data in the additional section.
val-log-level: <number>
Have the validator print validation failures to the log. Re-
gardless of the verbosity setting. Default is 0, off. At 1,
for every user query that fails a line is printed to the logs.
This way you can monitor what happens with validation. Use a
diagnosis tool, such as dig or drill, to find out why validation
is failing for these queries. At 2, not only the query that
failed is printed but also the reason why Unbound thought it was
wrong and which server sent the faulty data.
val-permissive-mode: <yes or no>
Instruct the validator to mark bogus messages as indeterminate.
The security checks are performed, but if the result is bogus
(failed security), the reply is not withheld from the client
with SERVFAIL as usual. The client receives the bogus data. For
messages that are found to be secure the AD bit is set in
replies. Also logging is performed as for full validation. The
default value is "no".
ignore-cd-flag: <yes or no>
Instruct Unbound to ignore the CD flag from clients and refuse
to 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. The default value is "no".
disable-edns-do: <yes or no>
Disable the EDNS DO flag in upstream requests. It breaks DNSSEC
validation for Unbound's clients. This results in the upstream
name servers to not include DNSSEC records in their replies and
could be helpful for devices that cannot handle DNSSEC 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 is no.
serve-expired: <yes or no>
If enabled, Unbound attempts to serve old responses from cache
with a TTL of serve-expired-reply-ttl in the response without
waiting for the actual resolution to finish. The actual resolu-
tion answer ends up in the cache later on. Default is "no".
serve-expired-ttl: <seconds>
Limit serving of expired responses to configured seconds after
expiration. 0 disables the limit. This option only applies when
serve-expired is enabled. A suggested value per RFC 8767 is be-
tween 86400 (1 day) and 259200 (3 days). The default is 0.
serve-expired-ttl-reset: <yes or no>
Set the TTL of expired records to the serve-expired-ttl value
after a failed attempt to retrieve the record from upstream.
This makes sure that the expired records will be served as long
as there are queries for it. Default is "no".
serve-expired-reply-ttl: <seconds>
TTL value to use when replying with expired data. If serve-ex-
pired-client-timeout is also used then it is RECOMMENDED to use
30 as the value (RFC 8767). The default is 30.
serve-expired-client-timeout: <msec>
Time in milliseconds before replying to the client with expired
data. This essentially enables the serve-stale behavior as
specified in RFC 8767 that first tries to resolve before immedi-
ately responding with expired data. A recommended value per RFC
8767 is 1800. Setting this to 0 will disable this behavior.
Default is 0.
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 that enabling this feature implicitly disables enforcement
of the configured minimum and maximum TTL, as it is assumed
users who enable this feature do not want Unbound to change the
TTL obtained from an upstream server. Thus, the values set us-
ing cache-min-ttl and cache-max-ttl are ignored. Default is
"no".
val-nsec3-keysize-iterations: <"list of values">
List of keysize and iteration count values, separated by spaces,
surrounded by quotes. Default is "1024 150 2048 150 4096 150".
This determines the maximum allowed NSEC3 iteration count before
a message is simply marked insecure instead of performing the
many hashing iterations. The list must be in ascending order and
have at least one entry. If you set it to "1024 65535" there is
no restriction to NSEC3 iteration values. This table must be
kept short; a very long list could cause slower operation.
zonemd-permissive-mode: <yes or no>
If enabled the ZONEMD verification failures are only logged and
do not cause the zone to be blocked and only return servfail.
Useful for testing out if it works, or if the operator only
wants to be notified of a problem without disrupting service.
Default is no.
add-holddown: <seconds>
Instruct the auto-trust-anchor-file probe mechanism for RFC5011
autotrust updates to add new trust anchors only after they have
been visible for this time. Default is 30 days as per the RFC.
del-holddown: <seconds>
Instruct the auto-trust-anchor-file probe mechanism for RFC5011
autotrust updates to remove revoked trust anchors after they
have been kept in the revoked list for this long. Default is 30
days as per the RFC.
keep-missing: <seconds>
Instruct the auto-trust-anchor-file probe mechanism for RFC5011
autotrust updates to remove missing trust anchors after they
have been unseen for this long. This cleans up the state file
if the target zone does not perform trust anchor revocation, so
this makes the auto probe mechanism work with zones that perform
regular (non-5011) rollovers. The default is 366 days. The
value 0 does not remove missing anchors, as per the RFC.
permit-small-holddown: <yes or no>
Debug option that allows the autotrust 5011 rollover timers to
assume very small values. Default is no.
key-cache-size: <number>
Number of bytes size of the key cache. Default is 4 megabytes.
A plain number is in bytes, append 'k', 'm' or 'g' for kilo-
bytes, megabytes or gigabytes (1024*1024 bytes in a megabyte).
key-cache-slabs: <number>
Number of slabs in the key cache. Slabs reduce lock contention
by threads. Must be set to a power of 2. Setting (close) to the
number of cpus is a reasonable guess.
neg-cache-size: <number>
Number of bytes size of the aggressive negative cache. Default
is 1 megabyte. A plain number is in bytes, append 'k', 'm' or
'g' for kilobytes, megabytes or gigabytes (1024*1024 bytes in a
megabyte).
unblock-lan-zones: <yes or no>
Default is disabled. If enabled, then for private address
space, the reverse lookups are no longer filtered. This allows
Unbound when running as dns service on a host where it provides
service for that host, to put out all of the queries for the
'lan' upstream. When enabled, only localhost, 127.0.0.1 reverse
and ::1 reverse zones are configured with default local zones.
Disable the option when Unbound is running as a (DHCP-) DNS net-
work resolver for a group of machines, where such lookups should
be filtered (RFC compliance), this also stops potential data
leakage about the local network to the upstream DNS servers.
insecure-lan-zones: <yes or no>
Default is disabled. If enabled, then reverse lookups in pri-
vate address space are not validated. This is usually required
whenever unblock-lan-zones is used.
local-zone: <zone> <type>
Configure a local zone. The type determines the answer to give
if there is no match from local-data. The types are deny,
refuse, static, transparent, redirect, nodefault, typetranspar-
ent, 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. An-
swers 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 answered.
Otherwise, the query is answered with nodata or nxdomain.
For a negative answer a SOA is included in the answer if
present as local-data for the zone apex domain.
transparent
If there is a match from local data, the query is answered.
Otherwise if the query has a different name, the query is re-
solved 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 de-
fault.
typetransparent
If there is a match from local data, the query is answered.
If the query is for a different name, or for the same name
but for a different type, the query is resolved normally.
So, similar to transparent but types that are not listed in
local data are resolved normally, so if an A record is in the
local data that does not cause a nodata reply for AAAA
queries.
redirect
The query is answered from the local data for the zone name.
There may be no local data beneath the zone name. This an-
swers queries for the zone, and all subdomains of the zone
with the local data for the zone. It can be used to redirect
a domain to return a different address record to the end
user, with local-zone: "example.com." redirect and lo-
cal-data: "example.com. A 127.0.0.1" queries for www.exam-
ple.com and www.foo.example.com are redirected, so that users
with web browsers cannot access sites with suffix exam-
ple.com.
inform
The query is answered normally, same as transparent. The
client IP address (@portnumber) is printed to the logfile.
The log message is: timestamp, unbound-pid, info: zonename
inform IP@port queryname type class. This option can be used
for normal resolution, but machines looking up infected names
are logged, eg. to run antivirus on them.
inform_deny
The query is dropped, like 'deny', and logged, like 'inform'.
Ie. find infected machines without answering the queries.
inform_redirect
The query is redirected, like 'redirect', and logged, like
'inform'. Ie. answer queries with fixed data and also log
the machines that ask.
always_transparent
Like transparent, but ignores local data and resolves nor-
mally.
block_a
Like transparent, but ignores local data and resolves nor-
mally all query types excluding A. For A queries it uncondi-
tionally 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 local
data in the zone. Used for some block lists.
noview
Breaks out of that view and moves towards the global local
zones for answer to the query. If the view first is no,
it'll resolve normally. If view first is enabled, it'll
break perform that step and check the global answers. For
when the view has view specific overrides but some zone has
to be answered from global local zone contents.
nodefault
Used to turn off default contents for AS112 zones. The other
types also turn off default contents for the zone. The 'node-
fault' option has no other effect than turning off default
contents for the given zone. Use nodefault if you use ex-
actly that zone, if you want to use a subzone, use transpar-
ent.
The default zones are localhost, reverse 127.0.0.1 and ::1, the
home.arpa, the onion, test, invalid and the AS112 zones. The AS112
zones are reverse DNS zones for private use and reserved IP addresses
for which the servers on the internet cannot provide correct answers.
They are configured by default to give nxdomain (no reverse informa-
tion) answers. The defaults can be turned off by specifying your own
local-zone of that name, or using the 'nodefault' type. Below is a list
of the default zone contents.
localhost
The IP4 and IP6 localhost information is given. NS and SOA
records are provided for completeness and to satisfy some DNS
update tools. Default content:
local-zone: "localhost." redirect
local-data: "localhost. 10800 IN NS localhost."
local-data: "localhost. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
local-data: "localhost. 10800 IN A 127.0.0.1"
local-data: "localhost. 10800 IN AAAA ::1"
reverse IPv4 loopback
Default content:
local-zone: "127.in-addr.arpa." static
local-data: "127.in-addr.arpa. 10800 IN NS localhost."
local-data: "127.in-addr.arpa. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
local-data: "1.0.0.127.in-addr.arpa. 10800 IN
PTR localhost."
reverse IPv6 loopback
Default content:
local-zone: "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa." static
local-data: "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa. 10800 IN
NS localhost."
local-data: "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
local-data: "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa. 10800 IN
PTR localhost."
home.arpa (RFC 8375)
Default content:
local-zone: "home.arpa." static
local-data: "home.arpa. 10800 IN NS localhost."
local-data: "home.arpa. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
onion (RFC 7686)
Default content:
local-zone: "onion." static
local-data: "onion. 10800 IN NS localhost."
local-data: "onion. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
test (RFC 6761)
Default content:
local-zone: "test." static
local-data: "test. 10800 IN NS localhost."
local-data: "test. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
invalid (RFC 6761)
Default content:
local-zone: "invalid." static
local-data: "invalid. 10800 IN NS localhost."
local-data: "invalid. 10800 IN
SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
reverse RFC1918 local use zones
Reverse data for zones 10.in-addr.arpa, 16.172.in-addr.arpa
to 31.172.in-addr.arpa, 168.192.in-addr.arpa. The lo-
cal-zone: is set static and as local-data: SOA and NS records
are provided.
reverse RFC3330 IP4 this, link-local, testnet and broadcast
Reverse data for zones 0.in-addr.arpa, 254.169.in-addr.arpa,
2.0.192.in-addr.arpa (TEST NET 1), 100.51.198.in-addr.arpa
(TEST NET 2), 113.0.203.in-addr.arpa (TEST NET 3),
255.255.255.255.in-addr.arpa. And from 64.100.in-addr.arpa
to 127.100.in-addr.arpa (Shared Address Space).
reverse RFC4291 IP6 unspecified
Reverse data for zone
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa.
reverse RFC4193 IPv6 Locally Assigned Local Addresses
Reverse data for zone D.F.ip6.arpa.
reverse RFC4291 IPv6 Link Local Addresses
Reverse data for zones 8.E.F.ip6.arpa to B.E.F.ip6.arpa.
reverse IPv6 Example Prefix
Reverse data for zone 8.B.D.0.1.0.0.2.ip6.arpa. This zone is
used for tutorials and examples. You can remove the block on
this zone with:
local-zone: 8.B.D.0.1.0.0.2.ip6.arpa. nodefault
You can also selectively unblock a part of the zone by making
that part transparent with a local-zone statement. This also
works with the other default zones.
local-data: "<resource record string>"
Configure local data, which is served in reply to queries for it.
The query has to match exactly unless you configure the local-zone
as redirect. If not matched exactly, the local-zone type deter-
mines further processing. If local-data is configured that is not
a subdomain of a local-zone, a transparent local-zone is config-
ured. For record types such as TXT, use single quotes, as in lo-
cal-data: 'example. TXT "text"'.
If you need more complicated authoritative data, with referrals,
wildcards, CNAME/DNAME support, or DNSSEC authoritative service,
setup a stub-zone for it as detailed in the stub zone section be-
low.
local-data-ptr: "IPaddr name"
Configure local data shorthand for a PTR record with the reversed
IPv4 or IPv6 address and the host name. For example "192.0.2.4
www.example.com". TTL can be inserted like this: "2001:DB8::4
7200 www.example.com"
local-zone-tag: <zone> <"list of tags">
Assign tags to localzones. Tagged localzones will only be applied
when the used access-control element has a matching tag. Tags must
be defined in define-tags. Enclose list of tags in quotes ("")
and put spaces between tags. When there are multiple tags it
checks if the intersection of the list of tags for the query and
local-zone-tag is non-empty.
local-zone-override: <zone> <IP netblock> <type>
Override the localzone type for queries from addresses matching
netblock. Use this localzone type, regardless the type configured
for the local-zone (both tagged and untagged) and regardless the
type configured using access-control-tag-action.
response-ip: <IP-netblock> <action>
This requires use of the "respip" module.
If the IP address in an AAAA or A RR in the answer section of a
response matches the specified IP netblock, the specified action
will apply. <action> has generally the same semantics as that for
access-control-tag-action, but there are some exceptions.
Actions for response-ip are different from those for local-zone in
that in case of the former there is no point of such conditions as
"the query matches it but there is no local data". Because of
this difference, the semantics of response-ip actions are modified
or simplified as follows: The static, refuse, transparent, type-
transparent, and nodefault actions are invalid for response-ip.
Using any of these will cause the configuration to be rejected as
faulty. The deny action is non-conditional, i.e. it always results
in dropping the corresponding query. The resolution result before
applying the deny action is still cached and can be used for other
queries.
response-ip-data: <IP-netblock> <"resource record string">
This requires use of the "respip" module.
This specifies the action data for response-ip with action being
to redirect as specified by "resource record string". "Resource
record string" is similar to that of access-control-tag-action,
but it must be of either AAAA, A or CNAME types. If the IP-net-
block is an IPv6/IPv4 prefix, the record must be AAAA/A respec-
tively, 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, fol-
lowing the normal rules for CNAME records. The textual domain
name for the CNAME does not have to be explicitly terminated with
a dot ("."); the root name is assumed to be the origin for the
name.
response-ip-tag: <IP-netblock> <"list of tags">
This requires use of the "respip" module.
Assign tags to response IP-netblocks. If the IP address in an
AAAA or A RR in the answer section of a response matches the spec-
ified IP-netblock, the specified tags are assigned to the IP ad-
dress. Then, if an access-control-tag is defined for the client
and it includes one of the tags for the response IP, the corre-
sponding access-control-tag-action will apply. Tag matching rule
is the same as that for access-control-tag and local-zones. Un-
like local-zone-tag, response-ip-tag can be defined for an IP-net-
block even if no response-ip is defined for that netblock. If
multiple response-ip-tag options are specified for the same IP-
netblock in different statements, all but the first will be ig-
nored. However, this will not be flagged as a configuration er-
ror, but the result is probably not what was intended.
Actions specified in an access-control-tag-action that has a
matching tag with response-ip-tag can be those that are "invalid"
for response-ip listed above, since access-control-tag-actions can
be shared with local zones. For these actions, if they behave
differently depending on whether local data exists or not in case
of local zones, the behavior for response-ip-data will generally
result in NOERROR/NODATA instead of NXDOMAIN, since the response-
ip data are inherently type specific, and non-existence of data
does not indicate anything about the existence or non-existence of
the qname itself. For example, if the matching tag action is
static but there is no data for the corresponding response-ip con-
figuration, then the result will be NOERROR/NODATA. The only case
where NXDOMAIN is returned is when an always_nxdomain action ap-
plies.
ratelimit: <number or 0>
Enable ratelimiting of queries sent to nameserver for performing
recursion. If 0, the default, it is disabled. This option is ex-
perimental at this time. The ratelimit is in queries per second
that are allowed. More queries are turned away with an error
(servfail). This stops recursive floods, eg. random query names,
but not spoofed reflection floods. Cached responses are not rate-
limited by this setting. The zone of the query is determined by
examining the nameservers for it, the zone name is used to keep
track of the rate. For example, 1000 may be a suitable value to
stop the server from being overloaded with random names, and keeps
Unbound from sending traffic to the nameservers for those zones.
Configured forwarders are excluded from ratelimiting.
ratelimit-size: <memory size>
Give the size of the data structure in which the current ongoing
rates are kept track in. Default 4m. In bytes or use m(mega),
k(kilo), g(giga). The ratelimit structure is small, so this data
structure likely does not need to be large.
ratelimit-slabs: <number>
Give power of 2 number of slabs, this is used to reduce lock con-
tention in the ratelimit tracking data structure. Close to the
number of cpus is a fairly good setting.
ratelimit-factor: <number>
Set the amount of queries to rate limit when the limit is 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 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 mit-
igating the traffic flow by the factor given.
ratelimit-backoff: <yes or no>
If enabled, the ratelimit is treated as a hard failure instead of
the default maximum allowed constant rate. When the limit is
reached, traffic is ratelimited and demand continues to be kept
track of for a 2 second rate window. No traffic is allowed, ex-
cept for ratelimit-factor, until demand decreases below the con-
figured ratelimit for a 2 second rate window. Useful to set rate-
limit to a suspicious rate to aggressively limit unusually high
traffic. Default is off.
ratelimit-for-domain: <domain> <number qps or 0>
Override the global ratelimit for an exact match domain name with
the listed number. You can give this for any number of names.
For example, for a top-level-domain you may want to have a higher
limit than other names. A value of 0 will disable ratelimiting
for that domain.
ratelimit-below-domain: <domain> <number qps or 0>
Override the global ratelimit for a domain name that ends in this
name. You can give this multiple times, it then describes differ-
ent 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 rate-
limit-for-domain to set that, you might want to use different set-
tings 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 completely
dropped and will not receive a reply, SERVFAIL or otherwise. IP
ratelimiting happens before looking in the cache. This may be use-
ful for mitigating amplification attacks. Clients with a valid
DNS Cookie will bypass the ratelimit. If a ratelimit for such
clients is still needed, ip-ratelimit-cookie can be used instead.
Default is 0 (disabled).
ip-ratelimit-cookie: <number or 0>
Enable global ratelimiting of queries accepted per IP address with
a valid DNS Cookie. This option is experimental at this time.
The ratelimit is in queries per second that are allowed. More
queries are completely dropped and will not receive a reply, SERV-
FAIL or otherwise. IP ratelimiting happens before looking in the
cache. This option could be useful in combination with al-
low_cookie in an attempt to mitigate other amplification attacks
than UDP reflections (e.g., attacks targeting Unbound itself)
which are already handled with DNS Cookies. If used, the value is
suggested to be higher than ip-ratelimit e.g., tenfold. Default
is 0 (disabled).
ip-ratelimit-size: <memory size>
Give the size of the data structure in which the current ongoing
rates are kept track in. Default 4m. In bytes or use m(mega),
k(kilo), g(giga). The ip ratelimit structure is small, so this
data structure likely does not need to be large.
ip-ratelimit-slabs: <number>
Give power of 2 number of slabs, this is used to reduce lock con-
tention in the ip ratelimit tracking data structure. Close to the
number of cpus is a fairly good setting.
ip-ratelimit-factor: <number>
Set the amount of queries to rate limit when the limit is 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 mit-
igating the traffic flow by the factor given.
ip-ratelimit-backoff: <yes or no>
If enabled, the ratelimit is treated as a hard failure instead of
the default maximum allowed constant rate. When the limit is
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 unusually
high traffic. Default is off.
outbound-msg-retry: <number>
The number of retries, per upstream nameserver in a delegation,
that Unbound will attempt in case a throwaway response is 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 is 5.
max-sent-count: <number>
Hard limit on the number of outgoing queries Unbound will make
while resolving a name, making sure large NS sets do not loop.
Results in SERVFAIL when reached. It resets on query restarts
(e.g., CNAME) and referrals. Default is 32.
max-query-restarts: <number>
Hard limit on the number of times Unbound is allowed to restart a
query upon encountering a CNAME record. Results in SERVFAIL when
reached. Changing this value needs caution as it can allow long
CNAME chains to be accepted, where Unbound needs to verify (re-
solve) each link individually. Default is 11.
fast-server-permil: <number>
Specify how many times out of 1000 to pick from the set of fastest
servers. 0 turns the feature off. A value of 900 would pick from
the fastest servers 90 percent of the time, and would perform nor-
mal 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 op-
tion can be used to specify the size of the fastest servers set.
The default for fast-server-permil is 0.
fast-server-num: <number>
Set the number of servers that should be used for fast server se-
lection. Only use the fastest specified number of servers with the
fast-server-permil option, that turns this on or off. The default
is to use the fastest 3 servers.
answer-cookie: <yes or no>
If enabled, Unbound will answer to requests containing DNS Cookies
as specified in RFC 7873 and RFC 9018. Default is no.
cookie-secret: <128 bit hex string>
Server's secret for DNS Cookie generation. Useful to explicitly
set for servers in an anycast deployment that need to share the
secret in order to verify each other's Server Cookies. An example
hex string would be "000102030405060708090a0b0c0d0e0f". Default
is a 128 bits random secret generated at startup time.
edns-client-string: <IP netblock> <string>
Include an EDNS0 option containing configured ascii string in
queries with destination address matching the configured IP net-
block. This configuration option can be used multiple times. The
most specific match will be used.
edns-client-string-opcode: <opcode>
EDNS0 option code for the edns-client-string option, from 0 to
65535. A value from the `Reserved for Local/Experimental` range
(65001-65534) should be used. Default is 65001.
ede: <yes or no>
If enabled, Unbound will respond with Extended DNS Error codes
(RFC8914). These EDEs attach informative error messages to a re-
sponse for various errors. Default is "no".
When the val-log-level option is also set to 2, responses with Ex-
tended DNS Errors concerning DNSSEC failures that are not served
from cache, will also contain a descriptive text message about the
reason for the failure.
ede-serve-expired: <yes or no>
If enabled, Unbound will attach an Extended DNS Error (RFC8914)
Code 3 - Stale Answer as EDNS0 option to the expired response.
Note that this will not attach the EDE code without setting the
global ede option to "yes" as well. Default is "no".
Remote Control Options
In the remote-control: clause are the declarations for the remote 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 un-
bound-control(8) utility also reads the remote-control section for op-
tions. 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, default is "no". If
turned off, the server does not listen for control commands.
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 per-
missions have been dropped, you must restart the server for the
change to take effect.
If you set it to an absolute path, a unix domain socket is used.
This socket does not use the certificates and keys, so those files
need not be present. To restrict access, Unbound sets permissions
on the file to the user and group that is configured, the access
bits are set to allow the group members to access the control
socket file. Put users that need to access the socket in the that
group. To restrict access further, create a directory to put the
control socket in and restrict access to that directory.
control-port: <port number>
The port number to listen on for IPv4 or IPv6 control interfaces,
default is 8953. If you change this and permissions have been
dropped, you must restart the server for the change to take ef-
fect.
control-use-cert: <yes or no>
For localhost control-interface you can disable the use of TLS by
setting this option to "no", default is "yes". For local sockets,
TLS is disabled and the value of this option is ignored.
server-key-file: <private key file>
Path to the server private key, by default unbound_server.key.
This file is generated by the unbound-control-setup utility. This
file is used by the Unbound server, but not by unbound-control.
server-cert-file: <certificate file.pem>
Path to the server self signed certificate, by default un-
bound_server.pem. This file is generated by the unbound-con-
trol-setup utility. This file is used by the Unbound server, and
also by unbound-control.
control-key-file: <private key file>
Path to the control client private key, by default unbound_con-
trol.key. This file is generated by the unbound-control-setup
utility. This file is used by unbound-control.
control-cert-file: <certificate file.pem>
Path to the control client certificate, by default unbound_con-
trol.pem. This certificate has to be signed with the server cer-
tificate. This file is generated by the unbound-control-setup
utility. This file is used by unbound-control.
Stub Zone Options
There may be multiple stub-zone: clauses. Each with a name: and zero or
more hostnames or IP addresses. For the stub zone this list of 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 lo-
cal-zone: name nodefault for the zone if it is a locally served zone.
The insecure clause stops DNSSEC from invalidating the zone. The local
zone nodefault (or transparent) clause makes the (reverse-) zone bypass
Unbound's filtering of RFC1918 zones.
name: <domain name>
Name of the stub zone. This is the full domain name of the zone.
stub-host: <domain name>
Name of stub zone nameserver. Is itself resolved before it is
used. To use a nondefault port for DNS communication append '@'
with the port number. If tls is enabled, then you can append a
'#' and a name, then it'll check the tls authentication certifi-
cates with that name. If you combine the '@' and '#', the '@'
comes first. If only '#' is used the default port is the con-
figured tls-port.
stub-addr: <IP address>
IP address of stub zone nameserver. Can be IP 4 or IP 6. To use
a nondefault port for DNS communication append '@' with the port
number. If tls is enabled, then you can append a '#' and a
name, then it'll check the tls authentication certificates with
that name. If you combine the '@' and '#', the '@' comes first.
If only '#' is used the default port is the configured tls-port.
stub-prime: <yes or no>
This option is by default no. If enabled it performs NS set
priming, which is similar to root hints, where it starts using
the list of nameservers currently published by the zone. Thus,
if the hint list is slightly outdated, the resolver picks up a
correct list online.
stub-first: <yes or no>
If enabled, a query is attempted without the stub clause if it
fails. The data could not be retrieved and would have caused
SERVFAIL because the servers are unreachable, instead it is
tried without this clause. The default is no.
stub-tls-upstream: <yes or no>
Enabled or disable whether the queries to this stub use TLS for
transport. Default is no.
stub-ssl-upstream: <yes or no>
Alternate syntax for stub-tls-upstream.
stub-tcp-upstream: <yes or no>
If it is set to "yes" then upstream queries use TCP only for
transport regardless of global flag tcp-upstream. Default is
no.
stub-no-cache: <yes or no>
Default is no. If enabled, data inside the stub is not cached.
This is useful when you want immediate changes to be visible.
Forward Zone Options
There may be multiple forward-zone: clauses. Each with a name: and zero
or more hostnames or IP addresses. For the forward zone this list of
nameservers is used to forward the queries to. The servers listed as
forward-host: and forward-addr: have to handle further recursion for
the query. Thus, those servers are not authority servers, but are
(just like Unbound is) recursive servers too; Unbound does not perform
recursion itself for the forward zone, it lets the remote server do it.
Class IN is assumed. CNAMEs are chased by Unbound itself, asking the
remote server for every name in the indirection chain, to protect the
local cache from illegal indirect referenced items. A forward-zone 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 nondefault port for DNS communication append '@'
with the port number. If tls is enabled, then you can append a
'#' and a name, then it'll check the tls authentication certifi-
cates with that name. If you combine the '@' and '#', the '@'
comes first. If only '#' is used the default port is the con-
figured tls-port.
forward-addr: <IP address>
IP address of server to forward to. Can be IP 4 or IP 6. To use
a nondefault port for DNS communication append '@' with the port
number. If tls is enabled, then you can append a '#' and a
name, then it'll check the tls authentication certificates with
that name. If you combine the '@' and '#', the '@' comes first.
If only '#' is used the default port is the configured tls-port.
At high verbosity it logs the TLS certificate, with TLS enabled.
If you leave out the '#' and auth name from the forward-addr,
any name is accepted. The cert must also match a CA from the
tls-cert-bundle.
forward-first: <yes or no>
If a forwarded query is met with a SERVFAIL error, and this 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. The default is "no".
forward-tls-upstream: <yes or no>
Enabled or disable whether the queries to this forwarder use TLS
for transport. Default is no. If you enable this, also config-
ure a tls-cert-bundle or use tls-win-cert to load CA certs, oth-
erwise the connections cannot be authenticated.
forward-ssl-upstream: <yes or no>
Alternate syntax for forward-tls-upstream.
forward-tcp-upstream: <yes or no>
If it is set to "yes" then upstream queries use TCP only for
transport regardless of global flag tcp-upstream. Default is
no.
forward-no-cache: <yes or no>
Default is no. If enabled, data inside the forward is not
cached. This is useful when you want immediate changes to be
visible.
Authority Zone Options
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 nondefault port for DNS communication append
'@' with the port number. You can append a '#' and a name, then
AXFR over TLS can be used and the tls authentication certifi-
cates will be checked with that name. If you combine the '@'
and '#', the '@' comes first. If you point it at another Un-
bound 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/exam-
ple.org.zone". Multiple url statements can be given, they are
tried in turn. If only urls are given the SOA refresh timer is
used to wait for making new downloads. If also primaries are
listed, the primaries are first probed with UDP SOA queries to
see if the SOA serial number has changed, reducing the number of
downloads. If none of the urls work, the primaries are tried
with IXFR and AXFR. For https, the tls-cert-bundle and the
hostname from the url are used to authenticate the connection.
If you specify a hostname in the URL, you cannot use the domain
from the zonefile, because it may not have that when retrieving
that data, instead use a plain IP address to avoid a circular
dependency on retrieving that IP address. Avoid dependencies on
name lookups by using a notation like "http://192.0.2.1/unbound-
primaries/example.com.zone", with an explicit IP address.
allow-notify: <IP address or host name 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. The primaries from primary: and url: statements
are allowed notify by default.
fallback-enabled: <yes or no>
Default no. If enabled, Unbound falls back to querying the in-
ternet as a resolver for this zone when lookups fail. For exam-
ple for DNSSEC validation failures.
for-downstream: <yes or no>
Default yes. If enabled, Unbound serves authority responses to
downstream clients for this zone. This option makes Unbound be-
have, for the queries with names in this zone, like one of the
authority servers for that zone. Turn it off if you want Un-
bound to provide recursion for the zone but have a local copy of
zone data. If for-downstream is no and for-upstream is yes,
then Unbound will DNSSEC validate the contents of the zone be-
fore serving the zone contents to clients and store validation
results in the cache.
for-upstream: <yes or no>
Default yes. If enabled, Unbound fetches data from this data
collection for answering recursion queries. Instead of sending
queries over the internet to the authority servers for this
zone, it'll fetch the data directly from the zone data. Turn it
on when you want Unbound to provide recursion for downstream
clients, and use the zone data as a local copy to speed up
lookups.
zonemd-check: <yes or no>
Enable this option to check ZONEMD records in the zone. Default
is disabled. The ZONEMD record is a checksum over the zone
data. This includes glue in the zone and data from the zone
file, and excludes comments from the zone file. When there is a
DNSSEC chain of trust, DNSSEC signatures are checked too.
zonemd-reject-absence: <yes or no>
Enable this option to reject the absence of the ZONEMD record.
Without it, when zonemd is not there it is not checked. It is
useful to enable for a nonDNSSEC signed zone where the operator
wants to require the verification of a ZONEMD, hence a missing
ZONEMD is a failure. The action upon failure is controlled by
the zonemd-permissive-mode option, for log only or also block
the zone. The default is no.
Without the option absence of a ZONEMD is only a failure when
the zone is DNSSEC signed, and we have a trust anchor, and the
DNSSEC verification of the absence of the ZONEMD fails. With
the option enabled, the absence of a ZONEMD is always a failure,
also for nonDNSSEC signed zones.
zonefile: <filename>
The filename where the zone is stored. If not given then no
zonefile is used. If the file does not exist or is empty, 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 elements. Views can also contain view-first,
response-ip, response-ip-data and local-data-ptr elements. View can be
mapped to requests by specifying the view name in an access-con-
trol-view element. Options from matching views will override global op-
tions. 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 ac-
cess-control-view elements.
local-zone: <zone> <type>
View specific local-zone elements. Has the same types and behav-
iour as the global local-zone elements. When there is at least
one local-zone specified and view-first is no, the default lo-
cal-zones will be added to this view. Defaults can be disabled
using the nodefault type. When view-first is yes or when a view
does not have a local-zone, the global local-zone will be used
including it's default zones.
local-data: "<resource record string>"
View specific local-data elements. Has the same behaviour as the
global local-data elements.
local-data-ptr: "IPaddr name"
View specific local-data-ptr elements. Has the same behaviour as
the global local-data-ptr elements.
view-first: <yes or no>
If enabled, it attempts to use the global local-zone and lo-
cal-data if there is no match in the view specific options. The
default is no.
Python Module Options
The python: clause gives the settings for the python(1) script module.
This module acts like the iterator and validator modules do, on queries
and answers. To enable the script module it has to be compiled into
the daemon, and the word "python" has to be put in the module-config:
option (usually first, or between the validator and iterator). Multiple
instances of the python module are supported by adding the word
"python" more than once.
If the chroot: option is enabled, you should make sure Python's library
directory structure is bind mounted in the new root environment, see
mount(8). Also the python-script: path should be specified as an abso-
lute path relative to the new root, or as a relative path to the work-
ing 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: option. 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: option, or as a relative path to the
working directory.
dynlib-file: <dynlib file>
The dynamic library file to load. Repeat this option for every
dynlib module instance added to the module-config: option.
DNS64 Module Options
The dns64 module must be configured in the module-config: "dns64 val-
idator iterator" directive and be compiled into the daemon to be en-
abled. These settings go in the server: section.
dns64-prefix: <IPv6 prefix>
This sets the DNS64 prefix to use to synthesize AAAA records
with. It must be /96 or shorter. The default prefix is
64:ff9b::/96.
dns64-synthall: <yes or no>
Debug option, default no. If enabled, synthesize all AAAA
records despite the presence of actual AAAA records.
dns64-ignore-aaaa: <name>
List domain for which the AAAA records are ignored and the A
record is used by dns64 processing instead. Can be entered 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. De-
faults to using the prefix configured in dns64-prefix, which in
turn defaults to 64:ff9b::/96. The prefix length must be one of
/32, /40, /48, /56, /64 or /96.
DNSCrypt Options
The dnscrypt: clause gives the settings of the dnscrypt channel. While
those options are available, they are only meaningful if Unbound was
compiled with --enable-dnscrypt. Currently certificate and secret/pub-
lic keys cannot be generated by Unbound. You can use dnscrypt-wrapper
to generate those: https://github.com/cofyc/dnscrypt-wrapper/blob/mas-
ter/README.md#usage
dnscrypt-enable: <yes or no>
Whether or not the dnscrypt config should be enabled. You may
define configuration but not activate it. The default is no.
dnscrypt-port: <port number>
On which port should dnscrypt should be activated. Note that you
should have a matching interface option defined in the server
section for this port.
dnscrypt-provider: <provider name>
The provider name to use to distribute certificates. This is of
the form: 2.dnscrypt-cert.example.com.. The name MUST end with a
dot.
dnscrypt-secret-key: <path to secret key file>
Path to the time limited secret key file. This option may be
specified multiple times.
dnscrypt-provider-cert: <path to cert file>
Path to the certificate related to the dnscrypt-secret-keys.
This option may be specified multiple times.
dnscrypt-provider-cert-rotated: <path to cert file>
Path to a certificate that we should be able to serve existing
connection from but do not want to advertise over
dnscrypt-provider's TXT record certs distribution. A typical
use case is when rotating certificates, existing clients may
still use the client magic from the old cert in their queries
until they fetch and update the new cert. Likewise, it would al-
low one to prime the new cert/key without distributing the new
cert yet, this can be useful when using a network of servers us-
ing anycast and on which the configuration may not get updated
at the exact same time. By priming the cert, the servers can
handle both old and new certs traffic while distributing only
one. This option may be specified multiple times.
dnscrypt-shared-secret-cache-size: <memory size>
Give the size of the data structure in which the shared secret
keys are kept in. Default 4m. In bytes or use m(mega),
k(kilo), g(giga). The shared secret cache is used when a same
client is making multiple queries using the same public key. It
saves a substantial amount of CPU.
dnscrypt-shared-secret-cache-slabs: <number>
Give power of 2 number of slabs, this is used to reduce lock
contention in the dnscrypt shared secrets cache. Close to the
number of cpus is a fairly good setting.
dnscrypt-nonce-cache-size: <memory size>
Give the size of the data structure in which the client nonces
are kept in. Default 4m. In bytes or use m(mega), k(kilo),
g(giga). The nonce cache is used to prevent dnscrypt message
replaying. Client nonce should be unique for any pair of client
pk/server sk.
dnscrypt-nonce-cache-slabs: <number>
Give power of 2 number of slabs, this is used to reduce lock
contention in the dnscrypt nonce cache. Close to the number of
cpus is a fairly good setting.
EDNS Client Subnet Module Options
The ECS module must be configured in the module-config: "subnetcache
validator iterator" directive and be compiled into the daemon to be en-
abled. 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, if
client-subnet-always-forward is set to yes. In this case the lookup in
the regular cache is skipped.
The maximum size of the ECS cache is controlled by 'msg-cache-size' in
the configuration file. On top of that, for each query only 100 differ-
ent subnets are allowed to be stored for each address family. Exceeding
that number, older entries will be purged from cache.
This module does not interact with the serve-expired* and prefetch: op-
tions.
send-client-subnet: <IP address>
Send client source address to this authority. Append /num to in-
dicate a classless delegation netblock, for example like
10.2.3.4/24 or 2001::11/64. Can be given multiple times. Author-
ities not listed will not receive edns-subnet information, un-
less 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 is no.
max-client-subnet-ipv6: <number>
Specifies the maximum prefix length of the client source address
we are willing to expose to third parties for IPv6. Defaults to
56.
max-client-subnet-ipv4: <number>
Specifies the maximum prefix length of the client source address
we are willing to expose to third parties for IPv4. Defaults to
24.
min-client-subnet-ipv6: <number>
Specifies the minimum prefix length of the IPv6 source mask we
are willing to accept in queries. Shorter source masks result in
REFUSED answers. Source mask of 0 is always accepted. Default is
0.
min-client-subnet-ipv4: <number>
Specifies the minimum prefix length of the IPv4 source mask we
are willing to accept in queries. Shorter source masks result in
REFUSED answers. Source mask of 0 is always accepted. Default is
0.
max-ecs-tree-size-ipv4: <number>
Specifies the maximum number of subnets ECS answers kept in the
ECS radix tree. This number applies for each qname/qclass/qtype
tuple. Defaults to 100.
max-ecs-tree-size-ipv6: <number>
Specifies the maximum number of subnets ECS answers kept in the
ECS radix tree. This number applies for each qname/qclass/qtype
tuple. Defaults to 100.
Opportunistic IPsec Support Module Options
The IPsec module must be configured in the module-config: "ipsecmod
validator iterator" directive and be compiled into Unbound by using
--enable-ipsecmod to be enabled. These settings go in the server: sec-
tion.
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 for-
mat.
IPSECKEY TTL
TTL of the IPSECKEY RRset.
A/AAAA
String of space separated IP addresses present in the A/AAAA
RRset. The IP addresses are in string format.
IPSECKEY
String of space separated IPSECKEY RDATA present in the
IPSECKEY RRset. The IPSECKEY RDATA are in DNS presentation
format.
The A/AAAA answer is then cached and returned to the client. If the
external hook was called the TTL changes to ensure it doesn't surpass
ipsecmod-max-ttl.
The same procedure is also followed when prefetch: is used, but the
A/AAAA answer is given to the client before the hook is called. ipsec-
mod-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: direc-
tive. This option facilitates turning on/off the module without
restarting/reloading Unbound. Defaults to yes.
ipsecmod-hook: <filename>
Specifies the external hook that Unbound will call with 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. Defaults to
no.
ipsecmod-max-ttl: <seconds>
Time to live maximum for A/AAAA cached records after calling the
external hook. Defaults to 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. Defaults to no.
ipsecmod-allow: <domain>
Allow the ipsecmod functionality for the domain so that the mod-
ule logic will be executed. Can be given multiple times, for
different domains. If the option is not specified, all domains
are treated as being allowed (default).
ipsecmod-whitelist: <yes or no>
Alternate syntax for ipsecmod-allow.
Cache DB Module Options
The Cache DB module must be configured in the module-config: "validator
cachedb iterator" directive and be compiled into the daemon with --en-
able-cachedb. If this module is enabled and configured, the specified
backend database works as a second level cache: When Unbound cannot
find an answer to a query in its built-in in-memory cache, it consults
the specified backend. If it finds a valid answer in the backend, Un-
bound 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. It should be noted that
Unbound never removes data stored in the Redis server, even if some
data have expired in terms of DNS TTL or the Redis server has cached
too much data; if necessary the Redis server must be configured to
limit the cache size, preferably with some kind of least-recently-used
eviction policy. Additionally, the redis-expire-records option can be
used in order to set the relative DNS TTL of the message as timeout to
the Redis records; keep in mind that some additional memory is used per
key and that the expire information is stored as absolute Unix time-
stamps in Redis (computer time must be stable). This backend uses syn-
chronous communication with the Redis server based on the assumption
that the communication is stable and sufficiently fast. The thread
waiting for a response from the Redis server cannot handle other DNS
queries. Although the backend has the ability to reconnect to the
server when the connection is closed unexpectedly and there is a con-
figurable timeout in case the server is overly slow or hangs up, these
cases are assumed to be very rare. If connection close or timeout hap-
pens too often, Unbound will be effectively unusable with this backend.
It's the administrator's responsibility to make the assumption hold.
The cachedb: clause gives custom settings of the cache DB module.
backend: <backend name>
Specify the backend database name. The default database is the
in-memory backend named "testframe", which, as the name sug-
gests, is not of any practical use. Depending on the build-time
configuration, "redis" backend may also be used as described
above.
secret-seed: <"secret string">
Specify a seed to calculate a hash value from query information.
This value will be used as the key of the corresponding answer
for the backend database and can be customized if the hash
should not be predictable operationally. If the backend data-
base is shared by multiple Unbound instances, all instances must
use the same secret seed. This option defaults to "default".
cachedb-no-store: <yes or no>
If the backend should be read from, but not written to. This
makes this instance not store dns messages in the backend. But
if data is available it is retrieved. The default is no.
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-ex-
pired-client-timeout, it then does not immediately respond 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 response is sent.
If also serve-expired-client-timeout is enabled, the expired re-
sponse is delayed until the timeout expires. Unless the lookup
succeeds within the timeout. The default is 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. This option de-
faults to "127.0.0.1".
redis-server-port: <port number>
The TCP port number of the Redis server. This option defaults
to 6379.
redis-server-path: <unix socket path>
The unix socket path to connect to the redis server. Off by de-
fault, and it can be set to "" to turn this off. Unix sockets
may have better throughput than the IP address option.
redis-server-password: "<password>"
The Redis AUTH password to use for the redis server. Only rele-
vant if Redis is configured for client password authorisation.
Off by default, and it can be set to "" to turn this off.
redis-timeout: <msec>
The period until when Unbound waits for a response from the Re-
dis sever. 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. This option defaults to 100 milliseconds.
redis-expire-records: <yes or no>
If Redis record expiration is enabled. If yes, Unbound sets
timeout for Redis records so that Redis can evict keys that have
expired automatically. If Unbound is configured with serve-ex-
pired and serve-expired-ttl is 0, this option is internally re-
verted to "no". Redis SETEX support is required for this option
(Redis >= 2.0.0). This option defaults to no.
redis-logical-db: <logical database index>
The logical database in Redis to use. These are databases in
the same Redis instance sharing the same configuration and 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. This option defaults to 0.
DNSTAP Logging Options
DNSTAP support, when compiled in by using --enable-dnstap, is enabled
in the dnstap: section. This starts an extra thread (when compiled
with threading) that writes the log information to the destination. If
Unbound is compiled without threading it does not spawn a thread, but
connects per-process to the destination.
dnstap-enable: <yes or no>
If dnstap is enabled. Default no. If yes, it connects to the
dnstap server and if any of the dnstap-log-..-messages options
is enabled it sends logs for those messages to the server.
dnstap-bidirectional: <yes or no>
Use frame streams in bidirectional mode to transfer DNSTAP mes-
sages. Default is yes.
dnstap-socket-path: <file name>
Sets the unix socket file name for connecting to the server that
is listening on that socket. Default is "".
dnstap-ip: <IPaddress[@port]>
If "", the unix socket is used, if set with an IP address (IPv4
or IPv6) that address is used to connect to the server.
dnstap-tls: <yes or no>
Set this to use TLS to connect to the server specified in
dnstap-ip. The default is yes. If set to no, TCP is used to
connect to the server.
dnstap-tls-server-name: <name of TLS authentication>
The TLS server name to authenticate the server with. Used when
dnstap-tls is enabled. If "" it is ignored, default "".
dnstap-tls-cert-bundle: <file name of cert bundle>
The pem file with certs to verify the TLS server certificate. If
"" the server default cert bundle is used, or the windows cert
bundle on windows. Default is "".
dnstap-tls-client-key-file: <file name>
The client key file for TLS client authentication. If "" client
authentication is not used. Default is "".
dnstap-tls-client-cert-file: <file name>
The client cert file for TLS client authentication. Default is
"".
dnstap-send-identity: <yes or no>
If enabled, the server identity is included in the log messages.
Default is no.
dnstap-send-version: <yes or no>
If enabled, the server version if included in the log messages.
Default is no.
dnstap-identity: <string>
The identity to send with messages, if "" the hostname is used.
Default is "".
dnstap-version: <string>
The version to send with messages, if "" the package version is
used. Default is "".
dnstap-log-resolver-query-messages: <yes or no>
Enable to log resolver query messages. Default is no. These
are messages from Unbound to upstream servers.
dnstap-log-resolver-response-messages: <yes or no>
Enable to log resolver response messages. Default is no. These
are replies from upstream servers to Unbound.
dnstap-log-client-query-messages: <yes or no>
Enable to log client query messages. Default is no. These are
client queries to Unbound.
dnstap-log-client-response-messages: <yes or no>
Enable to log client response messages. Default is no. These
are responses from Unbound to clients.
dnstap-log-forwarder-query-messages: <yes or no>
Enable to log forwarder query messages. Default is no.
dnstap-log-forwarder-response-messages: <yes or no>
Enable to log forwarder response messages. Default is no.
Response Policy Zone Options
Response Policy Zones are configured with rpz:, and each one must have
a name:. There can be multiple ones, by listing multiple rpz clauses,
each with a different name. RPZ clauses are applied in order of config-
uration. The respip module needs to be added to the module-config,
e.g.: module-config: "respip validator iterator".
QNAME, Response IP Address, nsdname, nsip and clientip triggers are
supported. Supported actions are: NXDOMAIN, NODATA, PASSTHRU, DROP,
Local Data, tcp-only and drop. RPZ QNAME triggers are applied after
local-zones and before auth-zones.
The rpz zone is formatted with a SOA start record as usual. The items
in the zone are entries, that specify what to act on (the trigger) and
what to do (the action). The trigger to act on is recorded in the
name, the action to do is recorded as the resource record. The names
all end in the zone name, so you could type the trigger names without a
trailing dot in the zonefile.
An example RPZ record, that answers example.com with NXDOMAIN
example.com CNAME .
The triggers are encoded in the name on the left
name query name
netblock.rpz-client-ip client IP address
netblock.rpz-ip response IP address in the answer
name.rpz-nsdname nameserver name
netblock.rpz-nsip nameserver IP address
The netblock is written as <netblocklen>.<ip address in reverse>. For
IPv6 use 'zz' for '::'. Specify individual addresses with scope length
of 32 or 128. For example, 24.10.100.51.198.rpz-ip is 198.51.100.10/24
and 32.10.zz.db8.2001.rpz-ip is 2001:db8:0:0:0:0:0:10/32.
The actions are specified with the record on the right
CNAME . nxdomain reply
CNAME *. nodata reply
CNAME rpz-passthru. do nothing, allow to continue
CNAME rpz-drop. the query is dropped
CNAME rpz-tcp-only. answer over TCP
A 192.0.2.1 answer with this IP address
Other records like AAAA, TXT and other CNAMEs (not rpz-..) can also be
used to answer queries with that content.
The RPZ zones can be configured in the config file with these settings
in the rpz: block.
name: <zone name>
Name of the authority zone.
primary: <IP address or host name>
Where to download a copy of the zone from, with AXFR and IXFR.
Multiple primaries can be specified. They are all tried if one
fails. To use a nondefault port for DNS communication append
'@' with the port number. You can append a '#' and a name, then
AXFR over TLS can be used and the tls authentication certifi-
cates will be checked with that name. If you combine the '@'
and '#', the '@' comes first. If you point it at another Un-
bound 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/exam-
ple.org.zone". Multiple url statements can be given, they are
tried in turn. If only urls are given the SOA refresh timer is
used to wait for making new downloads. If also primaries are
listed, the primaries are first probed with UDP SOA queries to
see if the SOA serial number has changed, reducing the number of
downloads. If none of the urls work, the primaries are tried
with IXFR and AXFR. For https, the tls-cert-bundle and the
hostname from the url are used to authenticate the connection.
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. The primaries from primary: and url: statements
are allowed notify by default.
zonefile: <filename>
The filename where the zone is stored. If not given then no
zonefile is used. If the file does not exist or is empty, 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 action are: nxdomain, nodata, passthru, drop, disabled
and cname.
rpz-cname-override: <domain>
The CNAME target domain to use if the cname action is configured
for rpz-action-override.
rpz-log: <yes or no>
Log all applied RPZ actions for this RPZ zone. Default is no.
rpz-log-name: <name>
Specify a string to be part of the log line, for easy 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 is no.
for-downstream: <yes or no>
If enabled the zone is authoritatively answered for and queries
for the RPZ zone information are answered to downstream clients.
This is useful for monitoring scripts, that can then access the
SOA information to check if the rpz information is up to date.
Default is no.
tags: <list of tags>
Limit the policies from this RPZ clause to clients with a match-
ing tag. Tags need to be defined in define-tag and can be as-
signed to client addresses using access-control-tag. Enclose
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 ser-
vice levels are lower, notable very large data and a high TCP load are
no longer supported. Very large data and high TCP loads are exceptional
for the DNS. DNSSEC validation is enabled, just add trust anchors. If
you do not have to worry about programs using more than 3 Mb of memory,
the below example is not for you. Use the defaults to receive full ser-
vice, 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-checkconf(8).
AUTHORS
Unbound was written by NLnet Labs. Please see CREDITS file in the dis-
tribution for further details.
NLnet Labs May 8, 2024 unbound.conf(5)
