unbound.conf(5) unbound 1.4.20 unbound.conf(5)NAMEunbound.conf - Unbound configuration file.
SYNOPSISunbound.confDESCRIPTIONunbound.conf is used to configure unbound(8). The file format has
attributes and values. Some attributes have attributes inside them.
The notation is: attribute: value.
Comments start with # and last to the end of line. Empty lines are
ignored as is whitespace at the beginning of a line.
The utility unbound-checkconf(8) can be used to check unbound.conf
prior to usage.
EXAMPLE
An example config file is shown below. Copy this to
/etc/unbound/unbound.conf and start the server with:
$ unbound -c /etc/unbound/unbound.conf
Most settings are the defaults. Stop the server with:
$ kill `cat /etc/unbound/unbound.pid`
Below is a minimal config file. The source distribution contains an
extensive example.conf file with all the options.
# unbound.conf(5) config file for unbound(8).
server:
directory: "/etc/unbound"
username: unbound
# make sure unbound can access entropy from inside the chroot.
# e.g. on linux the use these commands (on BSD, devfs(8) is used):
# mount --bind -n /dev/random /etc/unbound/dev/random
# and mount --bind -n /dev/log /etc/unbound/dev/log
chroot: "/etc/unbound"
# logfile: "/etc/unbound/unbound.log" #uncomment to use logfile.
pidfile: "/etc/unbound/unbound.pid"
# verbosity: 1 # uncomment and increase to get more logging.
# listen on all interfaces, answer queries from the local subnet.
interface: 0.0.0.0
interface: ::0
access-control: 10.0.0.0/8 allow
access-control: 2001:DB8::/64 allow
FILE FORMAT
There must be whitespace between keywords. Attribute keywords end with
a colon ':'. An attribute is followed by its containing attributes, or
a value.
Files can be included using the include: directive. It can appear any‐
where, it accepts a single file name as argument. Processing continues
as if the text from the included file was copied into the config file
at that point. If also using chroot, using full path names for the
included files works, relative pathnames for the included names work if
the directory where the daemon is started equals its chroot/working
directory. Wildcards can be used to include multiple files, see
glob(7).
Server Options
These options are part of the server: clause.
verbosity: <number>
The verbosity number, level 0 means no verbosity, only errors.
Level 1 gives operational information. Level 2 gives detailed
operational information. 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 command‐
line, see unbound(8).
statistics-interval: <seconds>
The number of seconds between printing statistics to the log for
every thread. Disable with value 0 or "". Default is disabled.
The histogram statistics are only printed if replies were sent
during the statistics interval, requestlist statistics are
printed for every interval (but can be 0). This is because the
median calculation requires data to be present.
statistics-cumulative: <yes or no>
If enabled, statistics are cumulative since starting unbound,
without clearing the statistics counters after logging the sta‐
tistics. Default is no.
extended-statistics: <yes or no>
If enabled, extended statistics are printed from unbound-con‐
trol(8). Default is off, because keeping track of more statis‐
tics takes time. The counters are listed in unbound-control(8).
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[@port]>
Interface to use to connect to the network. This interface is
listened to for queries from clients, and answers to clients are
given from it. Can be given multiple times to work on several
interfaces. If none are given the default is to listen to local‐
host. 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 spec‐
ified the default port (from port) is used.
interface-automatic: <yes or no>
Detect source interface on UDP queries and copy them to replies.
This feature is experimental, and needs support in your OS for
particular socket options. Default value is no.
outgoing-interface: <ip address>
Interface to use to connect to the network. This interface is
used to send queries to authoritative servers and receive their
replies. Can be given multiple times to work on several inter‐
faces. If none are given the default (all) is used. You can
specify the same interfaces in interface: and outgoing-inter‐
face: lines, the interfaces are then used for both purposes.
Outgoing queries are sent via a random outgoing interface to
counter spoofing.
outgoing-range: <number>
Number of ports to open. This number of file descriptors can be
opened per thread. Must be at least 1. Default depends on com‐
pile options. Larger numbers need extra resources from the oper‐
ating system. For performance a 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 per‐
mitted ports and subtracting the avoided ports from the set of
allowed ports. The processing starts with the non IANA allo‐
cated ports above 1024 in the set of allowed ports.
outgoing-port-avoid: <port number or range>
Do not permit unbound to open this port or range of ports for
use to send queries. Use this to make sure unbound does not grab
a port that another daemon needs. The port is avoided on all
outgoing interfaces, both IP4 and IP6. By default only ports
above 1024 that have not been assigned by IANA are used. Give a
port number or a range of the form "low-high", without spaces.
outgoing-num-tcp: <number>
Number of outgoing TCP buffers to allocate per thread. Default
is 10. If set to 0, or if do_tcp is "no", no TCP queries to
authoritative servers are done.
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.
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 4096 which is RFC recommended. If you have fragmen‐
tation reassembly problems, usually seen as timeouts, then a
value of 1480 can fix it. 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).
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 con‐
tention by threads. Must be set to a power of 2. Setting
(close) to the number of cpus is a reasonable guess.
num-queries-per-thread: <number>
The number of queries that every thread will service simultane‐
ously. If more queries arrive that need servicing, and no
queries can be jostled out (see jostle-timeout), then the
queries are dropped. This forces the client to resend after a
timeout; allowing the server time to work on the existing
queries. Default depends on compile options, 512 or 1024.
jostle-timeout: <msec>
Timeout used when the server is very busy. Set to a value that
usually results in one roundtrip to the authority servers. If
too many queries arrive, then 50% of the queries are allowed to
run to completion, and the other 50% are replaced with the new
incoming query if they have already spent more than their
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 (num‐
queriesperthread / 2) / (average time for such long queries)
qps. The qps for short queries can be about (numqueries‐
perthread / 2) / (jostletimeout in whole seconds) qps per
thread, about (1024/2)*5 = 2560 qps by default.
so-rcvbuf: <number>
If not 0, then set the SO_RCVBUF socket option to get more buf‐
fer space on UDP port 53 incoming queries. So that short spikes
on busy servers do not drop packets (see counter in netstat
-su). Default is 0 (use system value). Otherwise, the number
of bytes to ask for, try "4m" on a busy server. The OS caps it
at a maximum, on linux unbound needs root permission to bypass
the limit, or the admin can use sysctl net.core.rmem_max. On
BSD change kern.ipc.maxsockbuf in /etc/sysctl.conf. On OpenBSD
change header and recompile kernel. On Solaris ndd -set /dev/udp
udp_max_buf 8388608.
so-sndbuf: <number>
If not 0, then set the SO_SNDBUF socket option to get more buf‐
fer space on UDP port 53 outgoing queries. This for very busy
servers handles spikes in answer traffic, otherwise 'send:
resource temporarily unavailable' can get logged, the buffer
overrun is also visible by netstat -su. Default is 0 (use sys‐
tem 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.
rrset-cache-size: <number>
Number of bytes size of the RRset cache. Default is 4 megabytes.
A plain number is in bytes, append 'k', 'm' or 'g' for kilo‐
bytes, megabytes or gigabytes (1024*1024 bytes in a megabyte).
rrset-cache-slabs: <number>
Number of slabs in the RRset cache. Slabs reduce lock contention
by threads. Must be set to a power of 2.
cache-max-ttl: <seconds>
Time to live maximum for RRsets and messages in the cache.
Default is 86400 seconds (1 day). If the maximum kicks in,
responses to clients still get decrementing TTLs based on the
original (larger) values. When the internal 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.
cache-min-ttl: <seconds>
Time to live minimum for RRsets and messages in the cache.
Default is 0. If the 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.
infra-host-ttl: <seconds>
Time to live for entries in the host cache. The host cache con‐
tains roundtrip timing, lameness and EDNS support information.
Default is 900.
infra-cache-slabs: <number>
Number of slabs in the infrastructure cache. Slabs reduce lock
contention by threads. Must be set to a power of 2.
infra-cache-numhosts: <number>
Number of hosts for which information is cached. Default is
10000.
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.
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-upstream: <yes or no>
Enable or disable whether the upstream queries use TCP only for
transport. Default is no. Useful in tunneling scenarios.
ssl-upstream: <yes or no>
Enabled or disable whether the upstream queries use SSL only for
transport. Default is no. Useful in tunneling scenarios. The
SSL contains plain DNS in TCP wireformat. The other server must
support this (see ssl-service-key).
ssl-service-key: <file>
If enabled, the server provider SSL service on its TCP sockets.
The clients have to use ssl-upstream: yes. The file is the pri‐
vate key for the TLS session. The public certificate is in the
ssl-service-pem file. Default is "", turned off. Requires a
restart (a reload is not enough) if changed, because the private
key is read while root permissions are held and before chroot
(if any). Normal DNS TCP service is not provided and gives
errors, this service is best run with a different port: config
or @port suffixes in the interface config.
ssl-service-pem: <file>
The public key certificate pem file for the ssl service.
Default is "", turned off.
ssl-port: <number>
The port number on which to provide TCP SSL service, default
443, only interfaces configured with that port number as @number
get the SSL service.
do-daemonize: <yes or no>
Enable or disable whether the unbound server forks into the
background as a daemon. Default is yes.
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 or allow_snoop.
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 opera‐
tions where nonrecursive queries are made for the authoritative
data. For nonrecursive queries any replies from the dynamic
cache are refused.
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 pol‐
icy, and dropping may result in (possibly excessive) retried
queries.
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 por‐
tion.
The pidfile can be either a relative path to the working direc‐
tory, or an absolute path relative to the original root. It is
written just prior to chroot and dropping permissions. This
allows the pidfile to be /var/run/unbound.pid and the chroot to
be /var/unbound, for example.
Additionally, unbound may need to access /dev/random (for
entropy) from inside the chroot.
If given a chroot is done to the given directory. The default is
"/etc/unbound". If you give "" no chroot is performed.
username: <name>
If given, after binding the port the user privileges are
dropped. Default is "unbound". If you give username: "" no user
change is performed.
If this user is not capable of binding the port, reloads (by
signal HUP) will still retain the opened ports. If you change
the port number in the config file, and that new port number
requires privileges, then a reload will fail; a restart is
needed.
directory: <directory>
Sets the working directory for the program. Default is
"/etc/unbound".
logfile: <filename>
If "" is given, logging goes to stderr, or nowhere once daemo‐
nized. The logfile is appended to, in the following format:
[seconds since 1970] unbound[pid:tid]: type: message.
If this option is given, the use-syslog is option is set to
"no". The logfile is reopened (for append) when the config file
is reread, on SIGHUP.
use-syslog: <yes or no>
Sets unbound to send log messages to the syslogd, using sys‐
log(3). The log facility LOG_DAEMON is used, with identity
"unbound". The logfile setting is overridden when use-syslog is
turned on. The default is to log to syslog.
log-time-ascii: <yes or no>
Sets logfile lines to use a timestamp in UTC ascii. Default is
no, which prints the seconds since 1970 in brackets. No effect
if using syslog, in that case syslog formats the timestamp
printed into the log files.
log-queries: <yes or no>
Prints one line per query to the log, with the log timestamp and
IP address, name, type and class. Default is no. Note that it
takes time to print these lines which makes the server (signifi‐
cantly) slower. Odd (nonprintable) characters in names are
printed as '?'.
pidfile: <filename>
The process id is written to the file. Default is
"/var/run/unbound/unbound.pid". So,
kill -HUP `cat /var/run/unbound/unbound.pid`
triggers a reload,
kill -QUIT `cat /var/run/unbound/unbound.pid`
gracefully terminates.
root-hints: <filename>
Read the root hints from this file. Default is nothing, using
builtin hints for the IN class. The file has the format of zone
files, with root nameserver names and addresses only. The
default may become outdated, when servers change, therefore it
is good practice to use a root-hints file.
hide-identity: <yes or no>
If enabled id.server and hostname.bind queries are refused.
identity: <string>
Set the identity to report. If set to "", the default, then the
hostname of the server is returned.
hide-version: <yes or no>
If enabled version.server and version.bind queries are refused.
version: <string>
Set the version to report. If set to "", the default, then the
package version is returned.
target-fetch-policy: <"list of numbers">
Set the target fetch policy used by unbound to determine if it
should fetch nameserver target addresses opportunistically. The
policy is described per dependency depth.
The number of values determines the maximum dependency depth
that unbound will pursue in answering a query. A value of -1
means to fetch all targets opportunistically for that dependency
depth. A value of 0 means to fetch on demand only. A positive
value fetches that many targets opportunistically.
Enclose the list between quotes ("") and put spaces between num‐
bers. The default is "3 2 1 0 0". Setting all zeroes, "0 0 0 0
0" gives behaviour closer to that of BIND 9, while setting "-1
-1-1-1 -1" gives behaviour rumoured to be closer to that of
BIND 8.
harden-short-bufsize: <yes or no>
Very small EDNS buffer sizes from queries are ignored. Default
is off, since it is legal protocol wise to send these, and
unbound tries to give very small answers to these queries, where
possible.
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 on.
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 on.
harden-below-nxdomain: <yes or no>
From draft-vixie-dnsext-resimprove, returns nxdomain to queries
for a name below another name that is already known to be nxdo‐
main. 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 off.
harden-referral-path: <yes or no>
Harden the referral path by performing additional queries for
infrastructure data. Validates the replies if trust anchors are
configured and the zones are signed. This enforces DNSSEC vali‐
dation on nameserver NS sets and the nameserver addresses that
are encountered on the referral path to the answer. Default
off, because it burdens the authority servers, and it is not RFC
standard, and could lead to performance problems because of the
extra query load that is generated. Experimental option. If
you enable it consider adding more numbers after the tar‐
get-fetch-policy to increase the max depth that is checked to.
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.
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 occurence 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 addi‐
tional 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 spam‐
blocklists as they use that.
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.
rrset-roundrobin: <yes or no>
If yes, Unbound rotates RRSet order in response (the random num‐
ber is taken from the query ID, for speed and thread safety).
Default is no.
minimal-responses: <yes or no>
If yes, Unbound doesn't 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 no, because the DNS protocol RFCs mandate these
sections, and the additional content could be of use and save
roundtrips for clients.
module-config: <"module names">
Module configuration, a list of module names separated by spa‐
ces, surround the string with quotes (""). The modules can be
validator, iterator. Setting this to "iterator" will result in
a non-validating server. Setting this to "validator iterator"
will turn on DNSSEC validation. The ordering of the modules is
important. You must also set trust-anchors for validation to be
useful.
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 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.
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 addi‐
tion 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.
dlv-anchor-file: <filename>
File with trusted keys for DLV (DNSSEC Lookaside Validation).
Both DS and DNSKEY entries can be used in the file, in the same
format as for trust-anchor-file: statements. Only one DLV can be
configured, more would be slow. The DLV configured is used as a
root trusted DLV, this means that it is a lookaside for the
root. Default is "", or no dlv anchor file.
dlv-anchor: <"Resource Record">
Much like trust-anchor, this is a DLV anchor with the DS or
DNSKEY inline.
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. Also keys from DLV are
ignored for the domain. Can be given multiple times to specify
multiple domains that are treated as if unsigned. If you set
trust anchors for the domain they override this setting (and the
domain is secured).
This can be useful if you want to make sure a trust anchor for
external lookups does not affect an (unsigned) internal domain.
A DS record externally can create validation failures for that
internal domain.
val-override-date: <rrsig-style date spec>
Default is "" or "0", which disables this debugging feature. If
enabled by giving a RRSIG style date, that date is used for ver‐
ifying RRSIG inception and expiration dates, instead of the cur‐
rent date. Do not set this unless you are debugging signature
inception and expiration. The value -1 ignores the date alto‐
gether, useful for some special applications.
val-sig-skew-min: <seconds>
Minimum number of seconds of clock skew to apply to validated
signatures. A value of 10% of the signature lifetime (expira‐
tion - inception) is used, capped by this setting. Default is
3600 (1 hour) which allows for daylight savings differences.
Lower this value for more strict checking of short lived signa‐
tures.
val-sig-skew-max: <seconds>
Maximum number of seconds of clock skew to apply to validated
signatures. A value of 10% of the signature lifetime (expira‐
tion - inception) is used, capped by this setting. Default is
86400 (24 hours) which allows for timezone setting problems in
stable domains. Setting both min and max very low disables the
clock skew allowances. Setting both min and max very high makes
the validator check the signature timestamps less strictly.
val-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 sec‐
tion 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 protentially
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 Dis‐
abled) flag does not disable checking any more. This is useful
if legacy (w2008) servers that set the CD flag but cannot vali‐
date DNSSEC themselves are the clients, and then unbound pro‐
vides them with DNSSEC protection. The default value is "no".
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 500 4096 2500".
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.
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.
key-cache-size: <number>
Number of bytes size of the key cache. Default is 4 megabytes.
A plain number is in bytes, append 'k', 'm' or 'g' for kilo‐
bytes, megabytes or gigabytes (1024*1024 bytes in a megabyte).
key-cache-slabs: <number>
Number of slabs in the key cache. Slabs reduce lock contention
by threads. Must be set to a power of 2. Setting (close) to the
number of cpus is a reasonable guess.
neg-cache-size: <number>
Number of bytes size of the aggressive negative cache. Default
is 1 megabyte. A plain number is in bytes, append 'k', 'm' or
'g' for kilobytes, megabytes or gigabytes (1024*1024 bytes in a
megabyte).
local-zone: <zone> <type>
Configure a local zone. The type determines the answer to give
if there is no match from local-data. The types are deny,
refuse, static, transparent, redirect, nodefault, typetranspar‐
ent, 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.
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.exam‐
ple.com and www.foo.example.com are redirected, so that users
with web browsers cannot access sites with suffix exam‐
ple.com.
nodefault
Used to turn off default contents for AS112 zones. The other
types also turn off default contents for the zone. The 'node‐
fault' option has no other effect than turning off default
contents for the given zone.
The default zones are localhost, reverse 127.0.0.1 and ::1, 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 pro‐
vide 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." static
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."
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.
reverse RFC4291 IP6 unspecified
Reverse data for zone
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa.
reverse RFC4193 IPv6 Locally Assigned Local Addresses
Reverse data for zone D.F.ip6.arpa.
reverse RFC4291 IPv6 Link Local Addresses
Reverse data for zones 8.E.F.ip6.arpa to B.E.F.ip6.arpa.
reverse IPv6 Example Prefix
Reverse data for zone 8.B.D.0.1.0.0.2.ip6.arpa. This zone is
used for tutorials and examples. You can remove the block on
this zone with:
local-zone: 8.B.D.0.1.0.0.2.ip6.arpa. nodefault
You can also selectively unblock a part of the zone by making
that part transparent with a local-zone statement. This also
works with the other default zones.
local-data: "<resource record string>"
Configure local data, which is served in reply to queries for it.
The query has to match exactly unless you configure the local-zone
as redirect. If not matched exactly, the local-zone type deter‐
mines further processing. If local-data is configured that is not
a subdomain of a local-zone, a transparent local-zone is config‐
ured. For record types such as TXT, use single quotes, as in
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"
Remote Control Options
In the remote-control: clause are the declarations for the remote con‐
trol facility. If this is enabled, the unbound-control(8) utility can
be used to send commands to the running unbound server. The server
uses these clauses to setup SSLv3 / 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>
Give IPv4 or IPv6 addresses to listen on for control commands. By
default localhost (127.0.0.1 and ::1) is listened to. Use 0.0.0.0
and ::0 to listen to all interfaces.
control-port: <port number>
The port number to listen on for control commands, default is
8953. If you change this port number, and permissions have been
dropped, a reload is not sufficient to open the port again, you
must then restart.
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-con‐
trol-setup utility. This file is used by the unbound server, and
also by unbound-control.
control-key-file: <private key file>
Path to the control client private key, by default unbound_con‐
trol.key. This file is generated by the unbound-control-setup
utility. This file is used by unbound-control.
control-cert-file: <certificate file.pem>
Path to the control client certificate, by default unbound_con‐
trol.pem. This certificate has to be signed with the server cer‐
tificate. This file is generated by the unbound-control-setup
utility. This file is used by unbound-control.
Stub Zone Options
There may be multiple stub-zone: clauses. Each with a name: and zero or
more hostnames or IP addresses. For the stub zone this list of name‐
servers is used. Class IN is assumed. The servers should be authority
servers, not recursors; unbound performs the recursive processing
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 authorita‐
tive server, in which case a trusted key entry with the public key can
be put in config, so that unbound can validate the data and set the AD
bit on replies for the private zone (authoritative servers do not set
the AD bit). This setup makes unbound capable of answering queries for
the private zone, and can even set the AD bit ('authentic'), but the AA
('authoritative') bit is not set on these replies.
name: <domain name>
Name of the stub zone.
stub-host: <domain name>
Name of stub zone nameserver. Is itself resolved before it is
used.
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.
stub-prime: <yes or no>
This option is by default off. 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.
Forward Zone Options
There may be multiple forward-zone: clauses. Each with a name: and zero
or more hostnames or IP addresses. For the forward zone this list of
nameservers is used to forward the queries to. The servers listed as
forward-host: and forward-addr: have to handle further recursion for
the query. Thus, those servers are not authority servers, but are
(just like unbound is) recursive servers too; unbound does not perform
recursion itself for the forward zone, it lets the remote server do it.
Class IN is assumed. A forward-zone entry with name "." and a for‐
ward-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.
forward-host: <domain name>
Name of server to forward to. Is itself resolved before it is
used.
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.
forward-first: <yes or no>
If enabled, a query is attempted without the forward 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.
Python Module Options
The python: clause gives the settings for the python(1) script module.
This module acts like the iterator and validator modules do, on queries
and answers. To enable the script module it has to be compiled into
the daemon, and the word "python" has to be put in the module-config:
option (usually first, or between the validator and iterator).
python-script: <python file>
The script file to load.
MEMORY CONTROL EXAMPLE
In the example config settings below memory usage is reduced. Some ser‐
vice levels are lower, notable very large data and a high TCP load are
no longer supported. Very large data and high TCP loads are exceptional
for the DNS. DNSSEC validation is enabled, just add trust anchors. If
you do not have to worry about programs using more than 3 Mb of memory,
the below example is not for you. Use the defaults to receive full ser‐
vice, which on BSD-32bit tops out at 30-40 Mb after heavy usage.
# example settings that reduce memory usage
server:
num-threads: 1
outgoing-num-tcp: 1 # this limits TCP service, uses less buffers.
incoming-num-tcp: 1
outgoing-range: 60 # uses less memory, but less performance.
msg-buffer-size: 8192 # note this limits service, 'no huge stuff'.
msg-cache-size: 100k
msg-cache-slabs: 1
rrset-cache-size: 100k
rrset-cache-slabs: 1
infra-cache-numhosts: 200
infra-cache-slabs: 1
key-cache-size: 100k
key-cache-slabs: 1
neg-cache-size: 10k
num-queries-per-thread: 30
target-fetch-policy: "2 1 0 0 0 0"
harden-large-queries: "yes"
harden-short-bufsize: "yes"
FILES
/etc/unbound
default unbound working directory.
/etc/unbound
default chroot(2) location.
/etc/unbound/unbound.conf
unbound configuration file.
/var/run/unbound/unbound.pid
default unbound pidfile with process ID of the running daemon.
unbound.log
unbound log file. default is to log to syslog(3).
SEE ALSOunbound(8), unbound-checkconf(8).
AUTHORS
Unbound was written by NLnet Labs. Please see CREDITS file in the dis‐
tribution for further details.
NLnet Labs Mar 21, 2013 unbound.conf(5)
