NAME
unbound.conf - Unbound configuration file.
SYNOPSIS
unbound.conf
DESCRIPTION
unbound.conf is used to configure
unbound(8). The file format has
attributes and values. Some attributes have attributes inside them. The
notation is: attribute: value.
Comments start with # and last to the end of line. Empty lines are ignored as is
whitespace at the beginning of a line.
The utility
unbound-checkconf(8) can be used to check unbound.conf prior
to usage.
EXAMPLE
An example config file is shown below. Copy this to /etc/unbound/unbound.conf
and start the server with:
$ unbound -c /etc/unbound/unbound.conf
Most settings are the defaults. Stop the server with:
$ kill `cat /etc/unbound/unbound.pid`
Below is a minimal config file. The source distribution contains an extensive
example.conf file with all the options.
# unbound.conf(5) config file for unbound(8).
server:
directory: "/etc/unbound"
username: unbound
# make sure unbound can access entropy from inside the chroot.
# e.g. on linux the use these commands (on BSD, devfs(8) is used):
# mount --bind -n /dev/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
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. 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 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).
- 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 localhost. 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[@port]>
- Same as interface: (for easy of compatibility with
nsd.conf).
- 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 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.
- 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 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 4096 which is RFC
recommended. If you have fragmentation 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).
- 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.
- 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.
- 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 no. 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.
- 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-existant 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.
- 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 adress is down. Exists only on Linux, where the similar
ip-transparent option is also available.
- 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). 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 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.
- 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.
- 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.
- 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-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
private 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 853, 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, allow_snoop, deny_non_local or
refuse_non_local. The most specific netblock match is used, if none
match deny is used.
- 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 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.
- 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.
- 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 "/var/chroot/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
"/var/chroot/unbound/etc/unbound". On Windows the string
"%EXECUTABLE%" tries to change to the directory that unbound.exe
resides in.
- 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-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 '?'.
- pidfile: <filename>
- The process id is written to the file. Default is
"/var/run/unbound.pid". So,
kill -HUP `cat /var/run/unbound.pid`
triggers a reload,
kill -TERM `cat /var/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.
- 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 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
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 off.
Currently, draft-ietf-dnsop-nxdomain-cut promotes this technique.
- 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 off, because it burdens the
authority servers, and it is not RFC standard, and could lead to
performance problems because of the extra query load that is generated.
Experimental option. If you enable it consider adding more numbers after
the target-fetch-policy to increase the max depth that is checked to.
- 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-whitelist: <domain>
- Whitelist 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.
- qname-minimisation: <yes or no>
- Send minimum amount of information to upstream servers to
enhance privacy. Only sent minimum required labels of the QNAME and set
QTYPE to NS when possible. Best effort approach, full QNAME and original
QTYPE will be sent when upstream replies with a RCODE other than NOERROR.
Default is off.
- 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.
- 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 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.
- 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
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. 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).
- 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.
- dlv-anchor-file: <filename>
- This option was used during early days DNSSEC deployment
when no parent-side DS record registrations were easily available.
Nowadays, it is best to have DS records registered with the parent zone
(many top level zones are signed). 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 is going to be decommissioned.
Please do not use it any more.
- dlv-anchor: <"Resource
Record">
- Much like trust-anchor, this is a DLV anchor with the DS or
DNSKEY inline. DLV is going to be decommissioned. Please do not use it any
more.
- 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 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-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".
- 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.
- 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: <yesno>
- 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: <yesno>
- 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, 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.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. 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.
- 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 onion 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." 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."
- 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"
- 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"
- 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.
- 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-for-domain: <domain> <number
qps>
- 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.
- ratelimit-below-domain: <domain> <number
qps>
- 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.
Remote Control Options
In the
remote-control: clause are the declarations for the remote control
facility. If this is enabled, the
unbound-control(8) utility can be
used to send commands to the running unbound server. The server uses these
clauses to setup 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 or
path>
- Give IPv4 or IPv6 addresses or local socket path 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. If you
change this and permissions have been dropped, you must restart the server
for the change to take effect.
- 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>
- Whether to require certificate authentication of control
connections. The default is "yes". This should not be changed
unless there are other mechanisms in place to prevent untrusted users from
accessing the remote control interface.
- 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.
Stub Zone Options
There may be multiple
stub-zone: clauses. Each with a name: and zero or
more hostnames or IP addresses. For the stub zone this list of nameservers is
used. Class IN is assumed. The servers should be authority servers, not
recursors; unbound performs the recursive processing itself for stub zones.
The stub zone can be used to configure authoritative data to be used by the
resolver that cannot be accessed using the public internet servers. This is
useful for company-local data or private zones. Setup an authoritative server
on a different host (or different port). Enter a config entry for unbound with
stub-addr: <ip address of host[@port]>. The unbound resolver can
then access the data, without referring to the public internet for it.
This setup allows DNSSEC signed zones to be served by that authoritative server,
in which case a trusted key entry with the public key can be put in config, so
that unbound can validate the data and set the AD bit on replies for the
private zone (authoritative servers do not set the AD bit). This setup makes
unbound capable of answering queries for the private zone, and can even set
the AD bit ('authentic'), but the AA ('authoritative') bit is not set on these
replies.
Consider adding
server: statements for
domain-insecure: and for
local-zone: name nodefault for the zone if it is a locally
served zone. The insecure clause stops DNSSEC from invalidating the zone. The
local zone nodefault (or
transparent) clause makes the (reverse-) zone
bypass unbound's filtering of RFC1918 zones.
- name: <domain name>
- Name of the stub zone.
- 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 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.
- 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.
DNS64 Module Options
The dns64 module must be configured in the
module-config: "dns64
validator iterator" directive and be compiled into the daemon to be
enabled. These settings go in the
server: section.
- dns64-prefix: <IPv6 prefix>
- This sets the DNS64 prefix to use to synthesize AAAA
records with. It must be /96 or shorter. The default prefix is
64:ff9b::/96.
- dns64-synthall: <yes or no>
- Debug option, default no. If enabled, synthesize all AAAA
records despite the presence of actual AAAA records.
MEMORY CONTROL EXAMPLE
In the example config settings below memory usage is reduced. Some service
levels are lower, notable very large data and a high TCP load are no longer
supported. Very large data and high TCP loads are exceptional for the DNS.
DNSSEC validation is enabled, just add trust anchors. If you do not have to
worry about programs using more than 3 Mb of memory, the below example is not
for you. Use the defaults to receive full service, which on BSD-32bit tops out
at 30-40 Mb after heavy usage.
# example settings that reduce memory usage
server:
num-threads: 1
outgoing-num-tcp: 1 # this limits TCP service, uses less buffers.
incoming-num-tcp: 1
outgoing-range: 60 # uses less memory, but less performance.
msg-buffer-size: 8192 # note this limits service, 'no huge stuff'.
msg-cache-size: 100k
msg-cache-slabs: 1
rrset-cache-size: 100k
rrset-cache-slabs: 1
infra-cache-numhosts: 200
infra-cache-slabs: 1
key-cache-size: 100k
key-cache-slabs: 1
neg-cache-size: 10k
num-queries-per-thread: 30
target-fetch-policy: "2 1 0 0 0 0"
harden-large-queries: "yes"
harden-short-bufsize: "yes"
FILES
- /var/chroot/unbound/etc/unbound
- default unbound working directory.
- /var/chroot/unbound
- default chroot(2) location.
- /etc/unbound/unbound.conf
- unbound configuration file.
- /var/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).
SEE ALSO
unbound(8),
unbound-checkconf(8).
AUTHORS
Unbound was written by NLnet Labs. Please see CREDITS file in the
distribution for further details.