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