Provided by: unbound_1.9.4-2ubuntu1.9_amd64 bug

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 or is specified before the include statement with directory: dir.  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 ease 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 or ip6 netblock>
              Interface  to  use  to  connect  to  the  network.  This  interface  is  used  to  send queries to
              authoritative servers and receive their replies. Can be given multiple times to  work  on  several
              interfaces.  If  none  are given the default (all) is used. You can specify the same interfaces in
              interface: and outgoing-interface: lines, the interfaces are then used for both purposes. Outgoing
              queries are sent via a random outgoing interface to counter spoofing.

              If  an IPv6 netblock is specified instead of an individual IPv6 address, outgoing UDP queries will
              use a randomised source address taken from the netblock to counter  spoofing.  Requires  the  IPv6
              netblock  to  be routed to the host running unbound, and requires OS support for unprivileged non-
              local binds (currently only supported on Linux). Several netblocks may be specified with  multiple
              outgoing-interface:  options,  but  do  not  specify  both  an individual IPv6 address and an IPv6
              netblock, or the randomisation will be compromised.  Consider combining with  prefer-ip6:  yes  to
              increase  the  likelihood of IPv6 nameservers being selected for queries.  On Linux you need these
              two commands to be able to use the freebind socket option to receive traffic for the ip6 netblock:
              ip -6 addr add mynetblock/64 dev lo && ip -6 route add local mynetblock/64 dev lo

       outgoing-range: <number>
              Number  of  ports  to  open.  This number of file descriptors can be opened per thread. Must be at
              least 1. Default depends on  compile  options.  Larger  numbers  need  extra  resources  from  the
              operating system.  For performance a very large value is best, use libevent to make this possible.

       outgoing-port-permit: <port number or range>
              Permit  unbound  to  open this port or range of ports for use to send queries.  A larger number of
              permitted outgoing ports increases resilience against spoofing attempts. Make sure these ports are
              not needed by other daemons.  By default only ports above 1024 that have not been assigned by IANA
              are used.  Give a port number or a range of the form "low-high", without spaces.

              The outgoing-port-permit and outgoing-port-avoid statements are processed in the line order of the
              config  file, adding the permitted ports and subtracting the avoided ports from the set of allowed
              ports.  The processing starts with the non IANA allocated ports above 1024 in the set  of  allowed
              ports.

       outgoing-port-avoid: <port number or range>
              Do  not  permit  unbound  to open this port or range of ports for use to send queries. Use this to
              make sure unbound does not grab a port that another daemon needs.  The  port  is  avoided  on  all
              outgoing  interfaces,  both  IP4  and  IP6.   By  default only ports above 1024 that have not been
              assigned by IANA are used.  Give a port number or a range of the form "low-high", without spaces.

       outgoing-num-tcp: <number>
              Number of outgoing TCP buffers to allocate per thread. Default is 10. If set to 0, or if do-tcp is
              "no",  no TCP queries to authoritative servers are done.  For larger installations increasing this
              value is a good idea.

       incoming-num-tcp: <number>
              Number of incoming TCP buffers to allocate per thread. Default is 10. If set to 0, or if do-tcp is
              "no",  no TCP queries from clients are accepted. For larger installations increasing this value is
              a good idea.

       edns-buffer-size: <number>
              Number of bytes size to advertise as the EDNS reassembly buffer size.  This is the value put  into
              datagrams  over  UDP towards peers.  The actual buffer size is determined by msg-buffer-size (both
              for TCP and UDP).  Do not set higher than that value.  Default is 4096 which is  RFC  recommended.
              If  you have fragmentation reassembly problems, usually seen as timeouts, then a value of 1472 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.

       stream-wait-size: <number>
              Number of bytes size maximum to use for waiting stream buffers.  Default is 4 megabytes.  A  plain
              number  is in bytes, append 'k', 'm' or 'g' for kilobytes, megabytes or gigabytes (1024*1024 bytes
              in a megabyte).  As TCP and TLS streams queue up multiple results, the amount of memory  used  for
              these  buffers does not exceed this number, otherwise the responses are dropped.  This manages the
              total memory usage of the server (under heavy use), the number of requests that can be  queued  up
              per connection is also limited, with further requests waiting in TCP buffers.

       msg-buffer-size: <number>
              Number of bytes size of the message buffers. Default is 65552 bytes, enough for 64 Kb packets, the
              maximum DNS message size. No message larger than this can be sent or received. Can be  reduced  to
              use less memory, but some requests for DNS data, such as for huge resource records, will result in
              a SERVFAIL reply to the client.

       msg-cache-size: <number>
              Number of bytes size of the message cache. Default is 4 megabytes.  A plain number  is  in  bytes,
              append 'k', 'm' or 'g' for kilobytes, megabytes or gigabytes (1024*1024 bytes in a megabyte).

       msg-cache-slabs: <number>
              Number  of  slabs in the message cache. Slabs reduce lock contention by threads.  Must be set to a
              power of 2. Setting (close) to the number of cpus is a reasonable guess.

       num-queries-per-thread: <number>
              The number of queries that every thread will service simultaneously.  If more queries arrive  that
              need  servicing,  and  no  queries  can  be jostled out (see jostle-timeout), then the queries are
              dropped. This forces the client to resend after a timeout; allowing the server time to work on the
              existing queries. Default depends on compile options, 512 or 1024.

       jostle-timeout: <msec>
              Timeout  used  when the server is very busy.  Set to a value that usually results in one roundtrip
              to the authority servers.  If too many queries arrive, then 50% of the queries are allowed to  run
              to  completion,  and  the  other 50% are replaced with the new incoming query if they have already
              spent more than their allowed time.  This protects against denial of service by  slow  queries  or
              high  query rates.  Default 200 milliseconds.  The effect is that the qps for long-lasting queries
              is about (numqueriesperthread / 2) / (average time for such long queries) qps.  The qps for  short
              queries  can be about (numqueriesperthread / 2) / (jostletimeout in whole seconds) qps per thread,
              about (1024/2)*5 = 2560 qps by default.

       delay-close: <msec>
              Extra delay for timeouted UDP ports before they are closed, in  msec.   Default  is  0,  and  that
              disables it.  This prevents very delayed answer packets from the upstream (recursive) servers from
              bouncing against closed ports and setting off all sort of close-port counters, with eg. 1500 msec.
              When  timeouts  happen  you  need  extra  sockets,  it checks the ID and remote IP of packets, and
              unwanted packets are added to the unwanted packet counter.

       unknown-server-time-limit: <msec>
              The wait time in msec for waiting for an unknown server to reply.  Increase this if you are behind
              a slow satellite link, to eg. 1128.  That would then avoid re-querying every initial query because
              it times out.  Default is 376 msec.

       discard-timeout: <msec>
              The wait time in msec where recursion requests are dropped. This is to  stop  a  large  number  of
              replies  from  accumulating. They receive no reply, the work item continues to recurse. It is nice
              to be a bit larger than serve-expired-client-timeout if that is enabled.  A value of 1900 msec  is
              suggested. The value 0 disables it.  Default 1900 msec.

       wait-limit: <number>
              The  number of replies that can wait for recursion, for an IP address.  This makes a ratelimit per
              IP address of waiting replies for recursion.  It stops very large amounts of queries waiting to be
              returned to one destination. The value 0 disables wait limits. Default is 1000.

       wait-limit-netblock: <netblock> <number>
              The  wait  limit  for  the  netblock. If not given the wait-limit value is used. The most specific
              netblock is used to determine the limit. Useful for overriding the default for a  specific,  group
              or individual, server.  The value -1 disables wait limits for the netblock.

       so-rcvbuf: <number>
              If  not  0,  then set the SO_RCVBUF socket option to get more buffer space on UDP port 53 incoming
              queries.  So that short spikes on busy servers do not drop packets (see counter in  netstat  -su).
              Default  is  0  (use system value).  Otherwise, the number of bytes to ask for, try "4m" on a busy
              server.  The OS caps it at a maximum, on linux unbound needs root permission to bypass the  limit,
              or   the   admin   can  use  sysctl  net.core.rmem_max.   On  BSD  change  kern.ipc.maxsockbuf  in
              /etc/sysctl.conf.  On OpenBSD change header and recompile kernel. On  Solaris  ndd  -set  /dev/udp
              udp_max_buf 8388608.

       so-sndbuf: <number>
              If  not  0,  then set the SO_SNDBUF socket option to get more buffer space on UDP port 53 outgoing
              queries.  This for very busy servers handles spikes in answer traffic, otherwise  'send:  resource
              temporarily  unavailable'  can  get  logged,  the  buffer  overrun is also visible by netstat -su.
              Default is 0 (use system value).  Specify the number of bytes to ask for, try "4m" on a very  busy
              server.   The OS caps it at a maximum, on linux unbound needs root permission to bypass the limit,
              or the admin can use sysctl net.core.wmem_max.  On BSD, Solaris changes are similar to so-rcvbuf.

       so-reuseport: <yes or no>
              If yes, then open dedicated listening sockets for incoming queries for each thread and try to  set
              the  SO_REUSEPORT  socket  option on each socket.  May distribute incoming queries to threads more
              evenly.  Default is yes.  On Linux it is supported in kernels >= 3.9.  On other systems,  FreeBSD,
              OSX  it  may  also work.  You can enable it (on any platform and kernel), it then attempts to open
              the port and passes the option if it was available at compile time, if that works it is  used,  if
              it fails, it continues silently (unless verbosity 3) without the option.  At extreme load it could
              be better to turn it off to distribute the queries evenly, reported for Linux systems (4.4.x).

       ip-transparent: <yes or no>
              If yes, then use IP_TRANSPARENT socket option on sockets where unbound is listening  for  incoming
              traffic.   Default  no.  Allows you to bind to non-local interfaces.  For example for non-existent
              IP addresses that are going to exist later on, with host failover configuration.  This  is  a  lot
              like interface-automatic, but that one services all interfaces and with this option you can select
              which (future) interfaces unbound provides service on.  This option needs unbound  to  be  started
              with  root  permissions  on  some  systems.   The  option  uses  IP_BINDANY on FreeBSD systems and
              SO_BINDANY on OpenBSD systems.

       ip-freebind: <yes or no>
              If yes, then use IP_FREEBIND socket option on sockets  where  unbound  is  listening  to  incoming
              traffic.   Default no.  Allows you to bind to IP addresses that are nonlocal or do not exist, like
              when the network interface or IP address is  down.   Exists  only  on  Linux,  where  the  similar
              ip-transparent option is also available.

       rrset-cache-size: <number>
              Number  of  bytes  size  of  the RRset cache. Default is 4 megabytes.  A plain number is in bytes,
              append 'k', 'm' or 'g' for kilobytes, megabytes or gigabytes (1024*1024 bytes in a megabyte).

       rrset-cache-slabs: <number>
              Number of slabs in the RRset cache. Slabs reduce lock contention by threads.  Must  be  set  to  a
              power of 2.

       cache-max-ttl: <seconds>
              Time to live maximum for RRsets and messages in the cache. Default is 86400 seconds (1 day).  When
              the TTL expires, the cache item has expired.  Can be set lower to force the resolver to query  for
              data often, and not trust (very large) TTL values.  Downstream clients also see the lower TTL.

       cache-min-ttl: <seconds>
              Time to live minimum for RRsets and messages in the cache. Default is 0.  If the minimum kicks in,
              the data is cached for longer than the domain owner intended, and thus less queries  are  made  to
              look  up  the data.  Zero makes sure the data in the cache is as the domain owner intended, higher
              values, especially more than an hour or so, can lead to trouble as the data in the cache does  not
              match up with the actual data any more.

       cache-max-negative-ttl: <seconds>
              Time  to  live  maximum  for negative responses, these have a SOA in the authority section that is
              limited in time.  Default is 3600.  This applies to nxdomain and nodata answers.

       infra-host-ttl: <seconds>
              Time to live for entries in the host cache. The host cache contains roundtrip timing, lameness and
              EDNS support information. Default is 900.

       infra-cache-slabs: <number>
              Number  of slabs in the infrastructure cache. Slabs reduce lock contention by threads. Must be set
              to a power of 2.

       infra-cache-numhosts: <number>
              Number of hosts for which information is cached. Default is 10000.

       infra-cache-min-rtt: <msec>
              Lower limit for dynamic retransmit timeout calculation in  infrastructure  cache.  Default  is  50
              milliseconds.  Increase  this  value  if  using  forwarders needing more time to do recursive name
              resolution.

       define-tag: <"list of tags">
              Define the tags that can be used with local-zone and access-control.   Enclose  the  list  between
              quotes ("") and put spaces between tags.

       do-ip4: <yes or no>
              Enable or disable whether ip4 queries are answered or issued. Default is yes.

       do-ip6: <yes or no>
              Enable  or  disable  whether  ip6  queries  are  answered or issued. Default is yes.  If disabled,
              queries are not answered on IPv6, and queries are not sent on IPv6 to  the  internet  nameservers.
              With  this  option  you can disable the ipv6 transport for sending DNS traffic, it does not impact
              the contents of the DNS traffic, which may have ip4 and ip6 addresses in it.

       prefer-ip6: <yes or no>
              If enabled, prefer IPv6 transport for sending DNS queries to internet nameservers. Default is no.

       do-udp: <yes or no>
              Enable or disable whether UDP queries are answered or issued. Default is yes.

       do-tcp: <yes or no>
              Enable or disable whether TCP queries are answered or issued. Default is yes.

       tcp-mss: <number>
              Maximum segment size (MSS) of TCP socket on which the server responds to queries. Value lower than
              common  MSS  on  Ethernet  (1220  for  example)  will address path MTU problem.  Note that not all
              platform supports socket option to set MSS (TCP_MAXSEG).  Default is system default MSS determined
              by interface MTU and negotiation between server and client.

       outgoing-tcp-mss: <number>
              Maximum  segment  size  (MSS)  of TCP socket for outgoing queries (from Unbound to other servers).
              Value lower than common MSS on Ethernet (1220 for example) will address path  MTU  problem.   Note
              that  not  all platform supports socket option to set MSS (TCP_MAXSEG).  Default is system default
              MSS determined by interface MTU and negotiation between Unbound and other servers.

       tcp-idle-timeout: <msec>
              The period Unbound will wait for a query on a TCP connection.  If  this  timeout  expires  Unbound
              closes  the  connection.   This  option  defaults  to 30000 milliseconds.  When the number of free
              incoming TCP buffers falls below 50% of the total number configured,  the  option  value  used  is
              progressively  reduced,  first to 1% of the configured value, then to 0.2% of the configured value
              if the number of free buffers falls below 35% of the total number configured, and finally to 0  if
              the  number  of  free buffers falls below 20% of the total number configured. A minimum timeout of
              200 milliseconds is observed regardless of the option value used.

       edns-tcp-keepalive: <yes or no>
              Enable or disable EDNS TCP Keepalive. Default is no.

       edns-tcp-keepalive-timeout: <msec>
              The period Unbound will wait for a query on a TCP connection when EDNS TCP Keepalive is active. If
              this  timeout expires Unbound closes the connection. If the client supports the EDNS TCP Keepalive
              option, Unbound sends the timeout value to the client to encourage  it  to  close  the  connection
              before  the  server  times  out.  This option defaults to 120000 milliseconds.  When the number of
              free incoming TCP buffers falls below 50% of the total number configured, the  advertised  timeout
              is  progressively  reduced  to 1% of the configured value, then to 0.2% of the configured value if
              the number of free buffers falls below 35% of the total number configured, and finally to 0 if the
              number  of  free buffers falls below 20% of the total number configured.  A minimum actual timeout
              of 200 milliseconds is observed regardless of the advertised timeout.

       tcp-upstream: <yes or no>
              Enable or disable whether the upstream queries use TCP only for transport.  Default is no.  Useful
              in tunneling scenarios.

       udp-upstream-without-downstream: <yes or no>
              Enable  udp  upstream  even  if  do-udp  is no.  Default is no, and this does not change anything.
              Useful for TLS service providers, that want no udp downstream but use udp to fetch data upstream.

       tls-upstream: <yes or no>
              Enabled or disable whether the upstream queries use  TLS  only  for  transport.   Default  is  no.
              Useful  in  tunneling  scenarios.  The TLS contains plain DNS in TCP wireformat.  The other server
              must support this (see tls-service-key).  If you enable this, also configure a tls-cert-bundle  or
              use tls-win-cert to load CA certs, otherwise the connections cannot be authenticated.  This option
              enables TLS for all of them, but if you do not set this you can  configure  TLS  specifically  for
              some forward zones with forward-tls-upstream.  And also with stub-tls-upstream.

       ssl-upstream: <yes or no>
              Alternate syntax for tls-upstream.  If both are present in the config file the last is used.

       tls-service-key: <file>
              If  enabled,  the server provides TLS service on the TCP ports marked implicitly or explicitly for
              TLS service with tls-port.  The file must contain the private key for the TLS session, the  public
              certificate  is  in  the  tls-service-pem file and it must also be specified if tls-service-key is
              specified.  The default is "", turned off.  Enabling or disabling this service requires a  restart
              (a  reload  is  not  enough),  because  the key is read while root permissions are held and before
              chroot (if any).  The ports enabled implicitly or explicitly via tls-port: do not  provide  normal
              DNS TCP service.

       ssl-service-key: <file>
              Alternate syntax for tls-service-key.

       tls-service-pem: <file>
              The public key certificate pem file for the tls service.  Default is "", turned off.

       ssl-service-pem: <file>
              Alternate syntax for tls-service-pem.

       tls-port: <number>
              The  port number on which to provide TCP TLS service, default 853, only interfaces configured with
              that port number as @number get the TLS service.

       ssl-port: <number>
              Alternate syntax for tls-port.

       tls-cert-bundle: <file>
              If null  or  "",  no  file  is  used.   Set  it  to  the  certificate  bundle  file,  for  example
              "/etc/pki/tls/certs/ca-bundle.crt".   These  certificates  are used for authenticating connections
              made to outside peers.  For example auth-zone urls, and also DNS over TLS connections.

       ssl-cert-bundle: <file>
              Alternate syntax for tls-cert-bundle.

       tls-win-cert: <yes or no>
              Add the system certificates to the cert  bundle  certificates  for  authentication.   If  no  cert
              bundle,  it  uses  only  these  certificates.   Default  is  no.   On windows this option uses the
              certificates from the cert store.  Use the tls-cert-bundle option on other systems.

       tls-additional-port: <portnr>
              List portnumbers as tls-additional-port, and when interfaces  are  defined,  eg.  with  the  @port
              suffix,  as this port number, they provide dns over TLS service.  Can list multiple, each on a new
              statement.

       tls-session-ticket-keys: <file>
              If not "", lists files with 80 bytes of random contents that  are  used  to  perform  TLS  session
              resumption  for  clients using the unbound server.  These files contain the secret key for the TLS
              session tickets.  First key use to encrypt and decrypt TLS session tickets.   Other  keys  use  to
              decrypt  only.   With  this  you  can  roll  over  to new keys, by generating a new first file and
              allowing decrypt of the old file by listing it after the first file for some time, after the  wait
              clients  are not using the old key any more and the old key can be removed.  One way to create the
              file is dd if=/dev/random bs=1 count=80 of=ticket.dat The first 16 bytes should be different  from
              the  old one if you create a second key, that is the name used to identify the key.  Then there is
              32 bytes random data for an AES key and then 32 bytes random data for the HMAC key.

       tls-ciphers: <string with cipher list>
              Set the list of ciphers to allow when serving TLS.  Use "" for defaults, and that is the default.

       tls-ciphersuites: <string with ciphersuites list>
              Set the list of ciphersuites to allow when serving TLS.  This is for newer  TLS  1.3  connections.
              Use "" for defaults, and that is the default.

       use-systemd: <yes or no>
              Enable or disable systemd socket activation.  Default is no.

       do-daemonize: <yes or no>
              Enable or disable whether the unbound server forks into the background as a daemon.  Set the value
              to no when unbound runs as systemd service.  Default is yes.

       tcp-connection-limit: <IP netblock> <limit>
              Allow up to limit simultaneous TCP connections from  the  given  netblock.   When  at  the  limit,
              further  connections  are  accepted  but  closed immediately.  This option is experimental at this
              time.

       access-control: <IP netblock> <action>
              The netblock is given as an IP4 or IP6 address with /size appended for a classless network  block.
              The   action   can   be   deny,   refuse,   allow,  allow_setrd,  allow_snoop,  deny_non_local  or
              refuse_non_local.  The most specific netblock match is used, if none  match  deny  is  used.   The
              order of the access-control statements therefore does not matter.

              The action deny stops queries from hosts from that netblock.

              The action refuse stops queries too, but sends a DNS rcode REFUSED error message back.

              The  action  allow gives access to clients from that netblock.  It gives only access for recursion
              clients (which is what almost all clients need).  Nonrecursive queries are refused.

              The allow action does allow nonrecursive queries to access the local-data that is configured.  The
              reason  is  that  this  does not involve the unbound server recursive lookup algorithm, and static
              data is served in the reply.  This supports normal operations where nonrecursive queries are  made
              for  the  authoritative  data.   For  nonrecursive  queries any replies from the dynamic cache are
              refused.

              The allow_setrd action ignores the recursion desired (RD) bit and treats all requests  as  if  the
              recursion  desired bit is set.  Note that this behavior violates RFC 1034 which states that a name
              server should never perform recursive service unless asked via the RD bit  since  this  interferes
              with  trouble shooting of name servers and their databases. This prohibited behavior may be useful
              if another DNS server must forward requests for specific zones to a resolver DNS server, but  only
              supports stub domains and sends queries to the resolver DNS server with the RD bit cleared.

              The  action allow_snoop gives nonrecursive access too.  This give both recursive and non recursive
              access.  The name allow_snoop refers to cache snooping, a technique to use nonrecursive queries to
              examine  the  cache  contents  (for  malicious acts).  However, nonrecursive queries can also be a
              valuable debugging tool (when  you  want  to  examine  the  cache  contents).  In  that  case  use
              allow_snoop for your administration host.

              By  default  only localhost is allowed, the rest is refused.  The default is refused, because that
              is protocol-friendly. The DNS protocol is not designed to handle dropped packets  due  to  policy,
              and dropping may result in (possibly excessive) retried queries.

              The  deny_non_local and refuse_non_local settings are for hosts that are only allowed to query for
              the authoritative local-data, they are not allowed full recursion but only the static data.   With
              deny_non_local, messages that are disallowed are dropped, with refuse_non_local they receive error
              code REFUSED.

       access-control-tag: <IP netblock> <"list of tags">
              Assign tags to access-control elements. Clients using this access control element  use  localzones
              that are tagged with one of these tags. Tags must be defined in define-tags.  Enclose list of tags
              in quotes ("") and put spaces between tags. If access-control-tag is  configured  for  a  netblock
              that  does  not  have an access-control, an access-control element with action allow is configured
              for this netblock.

       access-control-tag-action: <IP netblock> <tag> <action>
              Set action for particular tag for given access control element. If you have multiple  tag  values,
              the  tag  used  to  lookup  the  action  is  the  first  tag  match between access-control-tag and
              local-zone-tag where "first" comes from the order of the define-tag values.

       access-control-tag-data: <IP netblock> <tag> <"resource record string">
              Set redirect data for particular tag for given access control element.

       access-control-view: <IP netblock> <view name>
              Set view for given access control element.

       chroot: <directory>
              If chroot is enabled, you should pass the configfile (from the commandline) as a  full  path  from
              the  original root. After the chroot has been performed the now defunct portion of the config file
              path is removed to be able to reread the config after a reload.

              All other file paths (working dir, logfile, roothints, and key files) can be specified in  several
              ways:  as  an absolute path relative to the new root, as a relative path to the working directory,
              or as an absolute path relative to the original root.  In the last case the path  is  adjusted  to
              remove the unused portion.

              The  pidfile  can be either a relative path to the working directory, or an absolute path relative
              to the original root. It is written just prior to chroot and dropping permissions. This allows the
              pidfile  to  be  /var/run/unbound.pid  and  the  chroot to be /var/unbound, for example. Note that
              Unbound is not able to remove the pidfile after termination when it  is  located  outside  of  the
              chroot directory.

              Additionally, unbound may need to access /dev/random (for entropy) from inside the chroot.

              If  given a chroot is done to the given directory. By default chroot is enabled and the default is
              "". If you give "" no chroot is performed.

       username: <name>
              If given, after binding the port the user privileges are dropped. Default  is  "unbound".  If  you
              give username: "" no user change is performed.

              If  this  user  is  not capable of binding the port, reloads (by signal HUP) will still retain the
              opened ports.  If you change the port number in the config file, and that new port number requires
              privileges, then a reload will fail; a restart is needed.

       directory: <directory>
              Sets  the  working  directory  for  the program. Default is "/etc/unbound".  On Windows the string
              "%EXECUTABLE%" tries to change to the directory that  unbound.exe  resides  in.   If  you  give  a
              server:  directory: dir before include: file statements then those includes can be relative to the
              working directory.

       logfile: <filename>
              If "" is given, logging goes to stderr, or nowhere once daemonized.  The logfile is  appended  to,
              in the following format:
              [seconds since 1970] unbound[pid:tid]: type: message.
              If  this  option  is given, the use-syslog is option is set to "no".  The logfile is reopened (for
              append) when the config file is reread, on SIGHUP.

       use-syslog: <yes or no>
              Sets unbound to send log messages to the syslogd, using syslog(3).  The log facility LOG_DAEMON is
              used,  with  identity  "unbound".  The logfile setting is overridden when use-syslog is turned on.
              The default is to log to syslog.

       log-identity: <string>
              If "" is given (default), then the name of the executable, usually "unbound" is used to report  to
              the  log.   Enter a string to override it with that, which is useful on systems that run more than
              one instance  of  unbound,  with  different  configurations,  so  that  the  logs  can  be  easily
              distinguished against.

       log-time-ascii: <yes or no>
              Sets  logfile lines to use a timestamp in UTC ascii. Default is no, which prints the seconds since
              1970 in brackets. No effect if using syslog, in that case syslog  formats  the  timestamp  printed
              into the log files.

       log-queries: <yes or no>
              Prints one line per query to the log, with the log timestamp and IP address, name, type and class.
              Default  is  no.   Note  that  it  takes  time  to  print  these  lines  which  makes  the  server
              (significantly) slower.  Odd (nonprintable) characters in names are printed as '?'.

       log-replies: <yes or no>
              Prints  one  line  per reply to the log, with the log timestamp and IP address, name, type, class,
              return code, time to resolve, from cache and response size.  Default is no.  Note  that  it  takes
              time  to  print  these  lines  which  makes the server (significantly) slower.  Odd (nonprintable)
              characters in names are printed as '?'.

       log-tag-queryreply: <yes or no>
              Prints the word 'query' and 'reply' with log-queries and log-replies.  This makes  filtering  logs
              easier.  The default is off (for backwards compatibility).

       log-local-actions: <yes or no>
              Print  log  lines  to  inform  about local zone actions.  These lines are like the local-zone type
              inform prints out, but they are also printed for the other types of local zones.

       log-servfail: <yes or no>
              Print log lines that say why queries return SERVFAIL  to  clients.   This  is  separate  from  the
              verbosity  debug  logs,  much smaller, and printed at the error level, not the info level of debug
              info from verbosity.

       pidfile: <filename>
              The process id is written to the file. Default is "/run/unbound.pid".  So,
              kill -HUP `cat /run/unbound.pid`
              triggers a reload,
              kill -TERM `cat /run/unbound.pid`
              gracefully terminates.

       root-hints: <filename>
              Read the root hints from this file. Default is nothing, using builtin hints for the IN class.  The
              file  has the format of zone files, with root nameserver names and addresses only. The default may
              become outdated, when servers change, therefore it is good practice to use a root-hints file.

       hide-identity: <yes or no>
              If enabled id.server and hostname.bind queries are refused.

       identity: <string>
              Set the identity to report. If set to "",  the  default,  then  the  hostname  of  the  server  is
              returned.

       hide-version: <yes or no>
              If enabled version.server and version.bind queries are refused.

       version: <string>
              Set the version to report. If set to "", the default, then the package version is returned.

       hide-trustanchor: <yes or no>
              If enabled trustanchor.unbound queries are refused.

       target-fetch-policy: <"list of numbers">
              Set  the  target  fetch  policy  used by unbound to determine if it should fetch nameserver target
              addresses opportunistically. The policy is described per dependency depth.

              The number of values determines the maximum dependency depth that unbound will pursue in answering
              a  query.  A value of -1 means to fetch all targets opportunistically for that dependency depth. A
              value of  0  means  to  fetch  on  demand  only.  A  positive  value  fetches  that  many  targets
              opportunistically.

              Enclose  the list between quotes ("") and put spaces between numbers.  The default is "3 2 1 0 0".
              Setting all zeroes, "0 0 0 0 0" gives behaviour closer to that of BIND 9, while setting "-1 -1  -1
              -1 -1" gives behaviour rumoured to be closer to that of BIND 8.

       harden-short-bufsize: <yes or no>
              Very  small EDNS buffer sizes from queries are ignored. Default is 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 RFC 8020 (with title "NXDOMAIN: There Really Is Nothing  Underneath"),  returns  nxdomain  to
              queries  for  a  name  below  another  name that is already known to be nxdomain.  DNSSEC mandates
              noerror for empty nonterminals, hence this is possible.  Very old software might  return  nxdomain
              for  empty  nonterminals  (that  usually  happen  for reverse IP address lookups), and thus may be
              incompatible with this.  To try to avoid this only DNSSEC-secure nxdomains are used,  because  the
              old  software does not have DNSSEC.  Default is on.  The nxdomain must be secure, this means nsec3
              with optout is insufficient.

       harden-referral-path: <yes or no>
              Harden the referral path by performing additional queries for infrastructure data.  Validates  the
              replies if trust anchors are configured and the zones are signed.  This enforces DNSSEC validation
              on nameserver NS sets and the nameserver addresses that are encountered on the  referral  path  to
              the answer.  Default no, because it burdens the authority servers, and it is not RFC standard, and
              could  lead  to  performance  problems  because  of  the  extra  query  load  that  is  generated.
              Experimental  option.  If you enable it consider adding more numbers after the target-fetch-policy
              to increase the max depth that is checked to.

       harden-algo-downgrade: <yes or no>
              Harden against algorithm downgrade when multiple algorithms are advertised in the DS  record.   If
              no,  allows the weakest algorithm to validate the zone.  Default is no.  Zone signers must produce
              zones that allow this feature to work, but sometimes they do not,  and  turning  this  option  off
              avoids that validation failure.

       use-caps-for-id: <yes or no>
              Use 0x20-encoded random bits in the query to foil spoof attempts.  This perturbs the lowercase and
              uppercase of query names sent to authority servers and checks if the reply still has  the  correct
              casing.  Disabled by default.  This feature is an experimental implementation of draft dns-0x20.

       caps-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 send minimum
              required labels of the QNAME and set QTYPE to A when possible. Best effort  approach;  full  QNAME
              and original QTYPE will be sent when upstream replies with a RCODE other than NOERROR, except when
              receiving NXDOMAIN from a DNSSEC signed zone. Default is yes.

       qname-minimisation-strict: <yes or no>
              QNAME minimisation in strict mode. Do not fall-back to sending full QNAME  to  potentially  broken
              nameservers.  A lot of domains will not be resolvable when this option in enabled. Only use if you
              know what you are doing.  This option only has effect when qname-minimisation is enabled.  Default
              is off.

       aggressive-nsec: <yes or no>
              Aggressive  NSEC  uses  the  DNSSEC  NSEC  chain  to  synthesize NXDOMAIN and other denials, using
              information from previous NXDOMAINs answers.  Default is no.  It helps to reduce  the  query  rate
              towards targets that get a very high nonexistent name lookup rate.

       private-address: <IP address or subnet>
              Give IPv4 of IPv6 addresses or classless subnets. These are addresses on your private network, and
              are not allowed to be returned for public internet names.  Any occurrence of  such  addresses  are
              removed  from  DNS  answers.  Additionally,  the DNSSEC validator may mark the answers bogus. This
              protects against so-called DNS Rebinding, where a user browser is turned  into  a  network  proxy,
              allowing remote access through the browser to other parts of your private network.  Some names can
              be allowed to contain your private addresses, by default all the local-data that you configured is
              allowed  to,  and you can specify additional names using private-domain.  No private addresses are
              enabled by default.  We consider to enable this for  the  RFC1918  private  IP  address  space  by
              default  in  later  releases.  That  would  enable  private addresses for 10.0.0.0/8 172.16.0.0/12
              192.168.0.0/16 169.254.0.0/16 fd00::/8 and fe80::/10, since the RFC standards say these  addresses
              should  not  be  visible  on  the  public  internet.   Turning  on  127.0.0.0/8  would hinder many
              spamblocklists as they use that.  Adding  ::ffff:0:0/96  stops  IPv4-mapped  IPv6  addresses  from
              bypassing the filter.

       private-domain: <domain name>
              Allow  this  domain,  and all its subdomains to contain private addresses.  Give multiple times to
              allow multiple domain names to contain private addresses. Default is none.

       unwanted-reply-threshold: <number>
              If set, a total number of unwanted replies is kept track of in every thread.  When it reaches  the
              threshold,  a defensive action is taken and a warning is printed to the log.  The defensive action
              is to clear the rrset and message caches, hopefully flushing away  any  poison.   A  value  of  10
              million is suggested.  Default is 0 (turned off).

       do-not-query-address: <IP address>
              Do  not  query  the  given  IP  address.  Can  be  IP4 or IP6. Append /num to indicate a classless
              delegation netblock, for example like 10.2.3.4/24 or 2001::11/64.

       do-not-query-localhost: <yes or no>
              If yes, localhost is added to the do-not-query-address entries, both IP6 ::1 and IP4  127.0.0.1/8.
              If no, then localhost can be used to send queries to. Default is yes.

       prefetch: <yes or no>
              If  yes,  message  cache  elements are prefetched before they expire to keep the cache up to date.
              Default is no.  Turning it on gives about 10 percent more traffic and load  on  the  machine,  but
              popular items do not expire from the cache.

       prefetch-key: <yes or no>
              If  yes,  fetch  the  DNSKEYs  earlier in the validation process, when a DS record is encountered.
              This lowers the latency of requests.  It does use a little more CPU.  Also if the cache is set  to
              0, it is no use. Default is no.

       deny-any: <yes or no>
              If  yes,  deny  queries  of type ANY with an empty response.  Default is no.  If disabled, unbound
              responds with a short list of resource records if some can be found in the  cache  and  makes  the
              upstream type ANY query if there are none.

       rrset-roundrobin: <yes or no>
              If yes, Unbound rotates RRSet order in response (the random number is taken from the query ID, for
              speed and thread safety).  Default is 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 yes,  even  though  the  DNS
              protocol  RFCs  mandate  these  sections,  and  the  additional  content  could be of use and save
              roundtrips for clients.  Because they are not used, and the saved roundtrips are easier saved with
              prefetch, whilst this is faster.

       disable-dnssec-lame-check: <yes or no>
              If  true,  disables  the  DNSSEC  lameness  check  in the iterator.  This check sees if RRSIGs are
              present in the answer, when dnssec is expected,  and  retries  another  authority  if  RRSIGs  are
              unexpectedly missing.  The validator will insist in RRSIGs for DNSSEC signed domains regardless of
              this setting, if a trust anchor is loaded.

       module-config: <"module names">
              Module configuration, a list of module names separated by spaces, surround the string with  quotes
              ("").  The  modules  can  be  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.  The default is "validator iterator".  When the server is built with  EDNS  client  subnet
              support the default is "subnetcache validator iterator".  Most modules that need to be listed here
              have to be listed at the beginning of the line.  The cachedb module has to be listed  just  before
              the  iterator.   The python module can be listed in different places, it then processes the output
              of the module it is just before.

       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), it must also be inside the chroot (if that is used).

       trust-anchor: <"Resource Record">
              A DS or DNSKEY RR for a key to use for validation.  Multiple  entries  can  be  given  to  specify
              multiple  trusted  keys, in addition to the trust-anchor-files.  The resource record is entered in
              the same format as 'dig' or 'drill' prints them, the same format as in the zone file. Has to be on
              a  single  line,  with  ""  around  it.  A  TTL can be specified for ease of cut and paste, but is
              ignored.  A class can be specified, but class IN is default.

       trusted-keys-file: <filename>
              File with trusted keys for validation. Specify more than one file with several entries,  one  file
              per  entry. Like trust-anchor-file but has a different file format. Format is BIND-9 style format,
              the trusted-keys { name flag proto algo "key"; };  clauses  are  read.   It  is  possible  to  use
              wildcards with this statement, the wildcard is expanded on start and on reload.

       trust-anchor-signaling: <yes or no>
              Send RFC8145 key tag query after trust anchor priming. Default is on.

       root-key-sentinel: <yes or no>
              Root key trust anchor sentinel. Default is on.

       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".

       serve-expired: <yes or no>
              If  enabled,  unbound  attempts  to serve old responses from cache with a TTL of 0 in the response
              without waiting for the actual resolution to finish.  The actual resolution answer ends up in  the
              cache later on.  Default is "no".

       serve-expired-ttl: <seconds>
              Limit  serving  of expired responses to configured seconds after expiration. 0 disables the limit.
              This option only applies when serve-expired is enabled. The default is 0.

       serve-expired-ttl-reset: <yes or no>
              Set the TTL of expired records to the serve-expired-ttl value after a failed attempt  to  retrieve
              the record from upstream. This makes sure that the expired records will be served as long as there
              are queries for it. Default is "no".

       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: <yes or no>
              Default  is  disabled.   If  enabled,  then  for private address space, the reverse lookups are no
              longer filtered.  This allows unbound when running as dns service on  a  host  where  it  provides
              service  for  that host, to put out all of the queries for the 'lan' upstream.  When enabled, only
              localhost, 127.0.0.1 reverse and ::1 reverse  zones  are  configured  with  default  local  zones.
              Disable  the  option  when  unbound  is  running  as a (DHCP-) DNS network resolver for a group of
              machines, where such lookups should be filtered (RFC compliance), this also stops  potential  data
              leakage about the local network to the upstream DNS servers.

       insecure-lan-zones: <yes or no>
              Default is disabled.  If enabled, then reverse lookups in private address space are not validated.
              This is usually required whenever unblock-lan-zones is used.

       local-zone: <zone> <type>
              Configure a local zone. The type determines  the  answer  to  give  if  there  is  no  match  from
              local-data. The types are deny, refuse, static, transparent, redirect, nodefault, typetransparent,
              inform, inform_deny, inform_redirect, always_transparent, always_refuse, always_nxdomain,  noview,
              and are explained below. After that the default settings are listed. Use local-data: to enter data
              into the local zone. Answers for local zones are authoritative DNS answers. By default  the  zones
              are class IN.

              If  you  need more complicated authoritative data, with referrals, wildcards, CNAME/DNAME support,
              or DNSSEC authoritative service, setup a stub-zone for it as detailed in  the  stub  zone  section
              below.

            deny Do  not  send  an  answer,  drop  the query.  If there is a match from local data, the query is
                 answered.

            refuse
                 Send an error message reply, with rcode REFUSED.  If there is a  match  from  local  data,  the
                 query is answered.

            static
                 If  there  is a match from local data, the query is answered.  Otherwise, the query is answered
                 with nodata or nxdomain.  For a negative answer a SOA is included in the answer if  present  as
                 local-data for the zone apex domain.

            transparent
                 If  there  is  a  match  from  local data, the query is answered.  Otherwise if the query has a
                 different name, the query is resolved normally.  If the query is for a name given in  localdata
                 but  no  such type of data is given in localdata, then a noerror nodata answer is returned.  If
                 no local-zone is given local-data causes a transparent zone to be created by default.

            typetransparent
                 If there is a match from local data, the query is answered.  If the query is  for  a  different
                 name,  or  for  the  same  name  but for a different type, the query is resolved normally.  So,
                 similar to transparent but types that are not listed in local data are resolved normally, so if
                 an A record is in the local data that does not cause a nodata reply for AAAA queries.

            redirect
                 The  query  is  answered  from  the  local  data for the zone name.  There may be no local data
                 beneath the zone name.  This answers queries for the zone, and all subdomains of the zone  with
                 the local data for the zone.  It can be used to redirect a domain to return a different address
                 record to the end user, with local-zone: "example.com." redirect and local-data:  "example.com.
                 A  127.0.0.1" queries for www.example.com and www.foo.example.com are redirected, so that users
                 with web browsers cannot access sites with suffix example.com.

            inform
                 The query is answered normally, same as transparent.  The client IP  address  (@portnumber)  is
                 printed  to  the  logfile.   The  log message is: timestamp, unbound-pid, info: zonename inform
                 IP@port queryname type class.  This option can be used  for  normal  resolution,  but  machines
                 looking up infected names are logged, eg. to run antivirus on them.

            inform_deny
                 The  query  is  dropped,  like  'deny',  and logged, like 'inform'.  Ie. find infected machines
                 without answering the queries.

            inform_redirect
                 The query is redirected, like 'redirect', and logged, like 'inform'.  Ie. answer  queries  with
                 fixed data and also log the machines that ask.

            always_transparent
                 Like transparent, but ignores local data and resolves normally.

            always_refuse
                 Like refuse, but ignores local data and refuses the query.

            always_nxdomain
                 Like static, but ignores local data and returns nxdomain for the query.

            noview
                 Breaks  out  of that view and moves towards the global local zones for answer to the query.  If
                 the view first is no, it'll resolve normally.  If view first is enabled,  it'll  break  perform
                 that step and check the global answers.  For when the view has view specific overrides but some
                 zone has to be answered from global local zone contents.

            nodefault
                 Used to turn off default contents for AS112 zones.  The  other  types  also  turn  off  default
                 contents  for  the  zone.  The  'nodefault' option has no other effect than turning off default
                 contents for the given zone.  Use nodefault if you use exactly that zone, if you want to use  a
                 subzone, use transparent.

       The default zones are localhost, reverse 127.0.0.1 and ::1, the onion, test, invalid and the AS112 zones.
       The AS112 zones are reverse DNS zones for private use and reserved IP addresses for which the servers  on
       the  internet cannot provide correct answers. They are configured by default to give nxdomain (no reverse
       information) answers. The defaults can be turned off by specifying your own local-zone of that  name,  or
       using the 'nodefault' type. Below is a list of the default zone contents.

            localhost
                 The  IP4  and  IP6  localhost  information  is  given.  NS  and  SOA  records  are provided for
                 completeness and to satisfy some DNS update tools. Default content:
                 local-zone: "localhost." redirect
                 local-data: "localhost. 10800 IN NS localhost."
                 local-data: "localhost. 10800 IN
                     SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
                 local-data: "localhost. 10800 IN A 127.0.0.1"
                 local-data: "localhost. 10800 IN AAAA ::1"

            reverse IPv4 loopback
                 Default content:
                 local-zone: "127.in-addr.arpa." static
                 local-data: "127.in-addr.arpa. 10800 IN NS localhost."
                 local-data: "127.in-addr.arpa. 10800 IN
                     SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
                 local-data: "1.0.0.127.in-addr.arpa. 10800 IN
                     PTR localhost."

            reverse IPv6 loopback
                 Default content:
                 local-zone: "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
                     0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa." static
                 local-data: "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
                     0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa. 10800 IN
                     NS localhost."
                 local-data: "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
                     0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa. 10800 IN
                     SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"
                 local-data: "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
                     0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa. 10800 IN
                     PTR localhost."

            onion (RFC 7686)
                 Default content:
                 local-zone: "onion." static
                 local-data: "onion. 10800 IN NS localhost."
                 local-data: "onion. 10800 IN
                     SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"

            test (RFC 2606)
                 Default content:
                 local-zone: "test." static
                 local-data: "test. 10800 IN NS localhost."
                 local-data: "test. 10800 IN
                     SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"

            invalid (RFC 2606)
                 Default content:
                 local-zone: "invalid." static
                 local-data: "invalid. 10800 IN NS localhost."
                 local-data: "invalid. 10800 IN
                     SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"

            reverse RFC1918 local use zones
                 Reverse  data  for   zones   10.in-addr.arpa,   16.172.in-addr.arpa   to   31.172.in-addr.arpa,
                 168.192.in-addr.arpa.   The local-zone: is set static and as local-data: SOA and NS records are
                 provided.

            reverse RFC3330 IP4 this, link-local, testnet and broadcast
                 Reverse data for zones 0.in-addr.arpa, 254.169.in-addr.arpa, 2.0.192.in-addr.arpa (TEST NET 1),
                 100.51.198.in-addr.arpa    (TEST    NET    2),    113.0.203.in-addr.arpa    (TEST    NET    3),
                 255.255.255.255.in-addr.arpa.  And from  64.100.in-addr.arpa  to  127.100.in-addr.arpa  (Shared
                 Address Space).

            reverse RFC4291 IP6 unspecified
                 Reverse data for zone
                 0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.
                 0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa.

            reverse RFC4193 IPv6 Locally Assigned Local Addresses
                 Reverse data for zone D.F.ip6.arpa.

            reverse RFC4291 IPv6 Link Local Addresses
                 Reverse data for zones 8.E.F.ip6.arpa to B.E.F.ip6.arpa.

            reverse IPv6 Example Prefix
                 Reverse  data  for zone 8.B.D.0.1.0.0.2.ip6.arpa. This zone is used for tutorials and examples.
                 You can remove the block on this zone with:
                   local-zone: 8.B.D.0.1.0.0.2.ip6.arpa. nodefault
                 You can also selectively unblock a part of the zone by making  that  part  transparent  with  a
                 local-zone statement.  This also works with the other default zones.

       local-data: "<resource record string>"
            Configure  local  data,  which is served in reply to queries for it.  The query has to match exactly
            unless you configure the local-zone as  redirect.  If  not  matched  exactly,  the  local-zone  type
            determines  further processing. If local-data is configured that is not a subdomain of a local-zone,
            a transparent local-zone is configured.  For record types such as TXT,  use  single  quotes,  as  in
            local-data: 'example. TXT "text"'.

            If  you need more complicated authoritative data, with referrals, wildcards, CNAME/DNAME support, or
            DNSSEC authoritative service, setup a stub-zone for it as detailed in the stub zone section below.

       local-data-ptr: "IPaddr name"
            Configure local data shorthand for a PTR record with the reversed IPv4 or IPv6 address and the  host
            name.   For  example  "192.0.2.4 www.example.com".  TTL can be inserted like this: "2001:DB8::4 7200
            www.example.com"

       local-zone-tag: <zone> <"list of tags">
            Assign tags to localzones. Tagged localzones will only  be  applied  when  the  used  access-control
            element  has  a  matching  tag. Tags must be defined in define-tags.  Enclose list of tags in quotes
            ("") and put spaces between tags.  When there are multiple tags it checks if the intersection of the
            list of tags for the query and local-zone-tag is non-empty.

       local-zone-override: <zone> <IP netblock> <type>
            Override  the localzone type for queries from addresses matching netblock.  Use this localzone type,
            regardless the type configured for the local-zone (both tagged and untagged) and regardless the type
            configured using access-control-tag-action.

       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 or 0>
            Override  the  global ratelimit for an exact match domain name with the listed number.  You can give
            this for any number of names.  For example, for a top-level-domain you may want  to  have  a  higher
            limit than other names.  A value of 0 will disable ratelimiting for that domain.

       ratelimit-below-domain: <domain> <number qps or 0>
            Override  the global ratelimit for a domain name that ends in this name.  You can give this multiple
            times, it then describes different settings in  different  parts  of  the  namespace.   The  closest
            matching  suffix is used to determine the qps limit.  The rate for the exact matching domain name is
            not changed, use ratelimit-for-domain to set that, you might want to use different  settings  for  a
            top-level-domain  and  subdomains.  A value of 0 will disable ratelimiting for domain names that end
            in this name.

       ip-ratelimit: <number or 0>
            Enable global ratelimiting of queries accepted per ip address.  If 0, the default, it  is  disabled.
            This  option is experimental at this time.  The ratelimit is in queries per second that are allowed.
            More queries are completely dropped and will  not  receive  a  reply,  SERVFAIL  or  otherwise.   IP
            ratelimiting  happens  before  looking in the cache. This may be useful for mitigating amplification
            attacks.

       ip-ratelimit-size: <memory size>
            Give the size of the data structure in which the current ongoing rates are kept track  in.   Default
            4m.   In  bytes or use m(mega), k(kilo), g(giga).  The ip ratelimit structure is small, so this data
            structure likely does not need to be large.

       ip-ratelimit-slabs: <number>
            Give power of 2 number of slabs, this is used to reduce lock contention in the ip ratelimit tracking
            data structure.  Close to the number of cpus is a fairly good setting.

       ip-ratelimit-factor: <number>
            Set  the  amount  of queries to rate limit when the limit is exceeded.  If set to 0, all queries are
            dropped for addresses where the limit is exceeded.  If set to another value, 1  in  that  number  is
            allowed  through to complete.  Default is 10, allowing 1/10 traffic to flow normally.  This can make
            ordinary queries complete (if repeatedly queried for), and enter the cache, whilst  also  mitigating
            the traffic flow by the factor given.

       fast-server-permil: <number>
            Specify  how  many  times  out of 1000 to pick from the set of fastest servers.  0 turns the feature
            off.  A value of 900 would pick from the fastest servers 90 percent of the time, and  would  perform
            normal  exploration  of  random  servers  for  the  remaining  time.  When  prefetch  is enabled (or
            serve-expired), such prefetches are not sped up, because there is no one  waiting  for  it,  and  it
            presents  a  good  moment  to  perform server exploration. The fast-server-num option can be used to
            specify the size of the fastest servers set. The default for fast-server-permil is 0.

       fast-server-num: <number>
            Set the number of servers that should be used for  fast  server  selection.  Only  use  the  fastest
            specified  number  of  servers  with  the  fast-server-permil option, that turns this on or off. The
            default is to use the fastest 3 servers.

   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 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.

            If you set it to an absolute path, a local socket is used.   The  local  socket  does  not  use  the
            certificates  and  keys,  so  those  files  need  not  be present.  To restrict access, unbound sets
            permissions on the file to the user and group that is configured, the access bits are set  to  allow
            the  group  members  to access the control socket file.  Put users that need to access the socket in
            the that group.  To restrict access further, create a directory to put the  control  socket  in  and
            restrict access to that directory.

       control-port: <port number>
            The  port  number  to listen on for IPv4 or IPv6 control interfaces, default is 8953.  If you change
            this and permissions have been dropped, you must restart the server for the change to take effect.

       control-use-cert: <yes or no>
            For localhost control-interface you can disable the use of TLS  by  setting  this  option  to  "no",
            default is "yes".  For local sockets, TLS is disabled and the value of this option is ignored.

       server-key-file: <private key file>
            Path  to  the  server  private  key,  by  default unbound_server.key.  This file is generated by the
            unbound-control-setup utility.  This file is used by the unbound server, but not by unbound-control.

       server-cert-file: <certificate file.pem>
            Path to the server self signed certificate, by default unbound_server.pem.  This file  is  generated
            by  the  unbound-control-setup  utility.   This  file  is  used  by  the unbound server, and also by
            unbound-control.

       control-key-file: <private key file>
            Path to the control client private key, by default unbound_control.key.  This file is  generated  by
            the unbound-control-setup utility.  This file is used by unbound-control.

       control-cert-file: <certificate file.pem>
            Path  to the control client certificate, by default unbound_control.pem.  This certificate has to be
            signed with the server certificate.  This file is generated by  the  unbound-control-setup  utility.
            This file is used by unbound-control.

   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 no.  If enabled it performs NS set priming, which is similar to root
              hints, where it starts using the list of nameservers currently published by the  zone.   Thus,  if
              the hint list is slightly outdated, the resolver picks up a correct list online.

       stub-first: <yes or no>
              If  enabled,  a  query  is  attempted  without the stub clause if it fails.  The data could not be
              retrieved and would have caused SERVFAIL because the servers are unreachable, instead it is  tried
              without this clause.  The default is no.

       stub-tls-upstream: <yes or no>
              Enabled or disable whether the queries to this stub use TLS for transport.  Default is no.

       stub-ssl-upstream: <yes or no>
              Alternate syntax for stub-tls-upstream.

       stub-no-cache: <yes or no>
              Default  is  no.   If  enabled,  data inside the stub is not cached.  This is useful when you want
              immediate changes to be visible.

   Forward Zone Options
       There may be multiple forward-zone: clauses. Each  with  a  name:  and  zero  or  more  hostnames  or  IP
       addresses.   For the forward zone this list of nameservers is used to forward the queries to. The servers
       listed as forward-host: and forward-addr: have to handle further recursion for the  query.   Thus,  those
       servers are not authority servers, but are (just like unbound is) recursive servers too; unbound does not
       perform recursion itself for the forward zone, it lets the remote server do it.   Class  IN  is  assumed.
       CNAMEs are chased by unbound itself, asking the remote server for every name in the indirection chain, to
       protect the local cache from illegal indirect referenced items.  A forward-zone 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.  If tls is enabled, then you can append a '#' and a
              name, then it'll check the tls authentication certificates with that name.  If you combine the '@'
              and '#', the '@' comes first.

              At high verbosity it logs the TLS certificate, with TLS enabled.  If you leave  out  the  '#'  and
              auth  name  from  the  forward-addr, any name is accepted.  The cert must also match a CA from the
              tls-cert-bundle.

       forward-first: <yes or no>
              If a forwarded query is met with a SERVFAIL error, and this option is enabled, unbound  will  fall
              back  to  normal recursive resolution for this query as if no query forwarding had been specified.
              The default is "no".

       forward-tls-upstream: <yes or no>
              Enabled or disable whether the queries to this forwarder use TLS for transport.   Default  is  no.
              If  you  enable  this,  also  configure  a  tls-cert-bundle  or use tls-win-cert to load CA certs,
              otherwise the connections cannot be authenticated.

       forward-ssl-upstream: <yes or no>
              Alternate syntax for forward-tls-upstream.

       forward-no-cache: <yes or no>
              Default is no.  If enabled, data inside the forward is not cached.  This is useful when  you  want
              immediate changes to be visible.

   Authority Zone Options
       Authority  zones  are  configured with auth-zone:, and each one must have a name:.  There can be multiple
       ones, by listing multiple auth-zone clauses, each with a different name, pertaining to that part  of  the
       namespace.   The authority zone with the name closest to the name looked up is used.  Authority zones are
       processed after local-zones and before cache (for-downstream: yes), and when used  in  this  manner  make
       unbound  respond  like  an authority server.  Authority zones are also processed after cache, just before
       going to the network to fetch information for recursion (for-upstream: yes), and when used in this manner
       provide a local copy of an authority server that speeds up lookups of that data.

       Authority  zones can be read from zonefile.  And can be kept updated via AXFR and IXFR.  After update the
       zonefile is rewritten.  The update mechanism uses the SOA timer values and performs SOA  UDP  queries  to
       detect zone changes.

       If  the  update  fetch fails, the timers in the SOA record are used to time another fetch attempt.  Until
       the SOA expiry timer is reached.  Then the zone  is  expired.   When  a  zone  is  expired,  queries  are
       SERVFAIL,  and  any  new  serial  number  is accepted from the master (even if older), and if fallback is
       enabled, the fallback activates to fetch from the upstream instead of the SERVFAIL.

       name: <zone name>
              Name of the authority zone.

       master: <IP address or host name>
              Where to download a copy of the zone from, with AXFR and IXFR.  Multiple masters can be specified.
              They are all tried if one fails.  With the "ip#name" notation a AXFR over TLS can be used.

       url: <url to zonefile>
              Where  to  download  a  zonefile  for  the  zone.   With http or https.  An example for the url is
              "http://www.example.com/example.org.zone".  Multiple url statements can be given, they  are  tried
              in  turn.   If only urls are given the SOA refresh timer is used to wait for making new downloads.
              If also masters are listed, the masters are first probed with UDP SOA queries to see  if  the  SOA
              serial  number  has  changed,  reducing  the  number  of downloads.  If none of the urls work, the
              masters are tried with IXFR and AXFR.  For https, the tls-cert-bundle and the  hostname  from  the
              url are used to authenticate the connection.

       allow-notify: <IP address or host name or netblockIP/prefix>
              With  allow-notify  you  can  specify  additional  sources of notifies.  When notified, the server
              attempts to first probe and then zone transfer.  If the notify is from a master, it first attempts
              that  master.  Otherwise other masters are attempted.  If there are no masters, but only urls, the
              file is downloaded when notified.  The masters from  master:  statements  are  allowed  notify  by
              default.

       fallback-enabled: <yes or no>
              Default  no.   If enabled, unbound falls back to querying the internet as a resolver for this zone
              when lookups fail.  For example for DNSSEC validation failures.

       for-downstream: <yes or no>
              Default yes.  If enabled, unbound serves authority responses to downstream clients for this  zone.
              This  option  makes  unbound  behave,  for  the  queries  with names in this zone, like one of the
              authority servers for that zone.  Turn it off if you want unbound to  provide  recursion  for  the
              zone  but  have  a local copy of zone data.  If for-downstream is no and for-upstream is yes, then
              unbound will DNSSEC validate the contents of the zone before serving the zone contents to  clients
              and store validation results in the cache.

       for-upstream: <yes or no>
              Default  yes.   If enabled, unbound fetches data from this data collection for answering recursion
              queries.  Instead of sending queries over the internet to the authority  servers  for  this  zone,
              it'll  fetch  the  data  directly from the zone data.  Turn it on when you want unbound to provide
              recursion for downstream clients, and use the zone data as a local copy to speed up lookups.

       zonefile: <filename>
              The filename where the zone is stored.  If not given then no zonefile is used.  If the  file  does
              not exist or is empty, unbound will attempt to fetch zone data (eg. from the master servers).

   View Options
       There  may  be  multiple  view:  clauses.  Each  with  a name: and zero or more local-zone and local-data
       elements. Views can also contain view-first, response-ip, response-ip-data and  local-data-ptr  elements.
       View  can  be  mapped  to requests by specifying the view name in an access-control-view element. Options
       from matching views will override global options. Global options will be used  if  no  matching  view  is
       found, or when the matching view does not have the option specified.

       name: <view name>
              Name of the view. Must be unique. This name is used in access-control-view elements.

       local-zone: <zone> <type>
              View  specific  local-zone  elements.  Has  the  same types and behaviour as the global local-zone
              elements. When there is at least one local-zone specified and view-first is no, the default local-
              zones  will  be  added  to  this  view.   Defaults  can be disabled using the nodefault type. When
              view-first is yes or when a view does not have a local-zone, the global local-zone  will  be  used
              including it's default zones.

       local-data: "<resource record string>"
              View specific local-data elements. Has the same behaviour as the global local-data elements.

       local-data-ptr: "IPaddr name"
              View  specific  local-data-ptr  elements.  Has  the  same  behaviour  as the global local-data-ptr
              elements.

       view-first: <yes or no>
              If enabled, it attempts to use the global local-zone and local-data if there is no  match  in  the
              view specific options.  The default is no.

   Python Module Options
       The  python:  clause  gives  the  settings  for  the  python(1) script module.  This module acts like the
       iterator and validator modules do, on queries and answers.  To enable the script  module  it  has  to  be
       compiled  into  the  daemon,  and  the  word "python" has to be put in the module-config: option (usually
       first, or between the validator and iterator). Multiple instances of the python module are  supported  by
       adding the word "python" more than once.

       If  the  chroot:  option  is  enabled,  you should make sure Python's library directory structure is bind
       mounted in the new root environment, see mount(8).  Also the python-script: path should be  specified  as
       an absolute path relative to the new root, or as a relative path to the working directory.

       python-script: <python file>
              The  script  file  to  load.  Repeat  this  option  for  every python module instance added to the
              module-config: option.

   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.

       dns64-ignore-aaaa: <name>
              List  domain  for  which the AAAA records are ignored and the A record is used by dns64 processing
              instead.  Can be entered multiple times, list a new domain for which it  applies,  one  per  line.
              Applies also to names underneath the name given.

   DNSCrypt Options
       The  dnscrypt: clause gives the settings of the dnscrypt channel. While those options are available, they
       are  only  meaningful  if  unbound  was  compiled  with  --enable-dnscrypt.   Currently  certificate  and
       secret/public  keys  cannot  be  generated  by  unbound.  You can use dnscrypt-wrapper to generate those:
       https://github.com/cofyc/dnscrypt-wrapper/blob/master/README.md#usage

       dnscrypt-enable: <yes or no>
              Whether or not the dnscrypt config should  be  enabled.  You  may  define  configuration  but  not
              activate it.  The default is no.

       dnscrypt-port: <port number>
              On  which port should dnscrypt should be activated. Note that you should have a matching interface
              option defined in the server section for this port.

       dnscrypt-provider: <provider name>
              The  provider  name  to  use  to  distribute  certificates.  This  is  of  the  form:  2.dnscrypt-
              cert.example.com.. The name MUST end with a dot.

       dnscrypt-secret-key: <path to secret key file>
              Path to the time limited secret key file. This option may be specified multiple times.

       dnscrypt-provider-cert: <path to cert file>
              Path  to  the  certificate  related  to  the  dnscrypt-secret-keys.   This option may be specified
              multiple times.

       dnscrypt-provider-cert-rotated: <path to cert file>
              Path to a certificate that we should be able to serve existing connection from but do not want  to
              advertise  over  dnscrypt-provider's  TXT  record  certs distribution.  A typical use case is when
              rotating certificates, existing clients may still use the client magic from the old cert in  their
              queries  until  they  fetch and update the new cert. Likewise, it would allow one to prime the new
              cert/key without distributing the new cert yet, this can be useful when using a network of servers
              using  anycast  and  on  which  the  configuration  may not get updated at the exact same time. By
              priming the cert, the servers can handle both old and new certs traffic  while  distributing  only
              one.  This option may be specified multiple times.

       dnscrypt-shared-secret-cache-size: <memory size>
              Give  the size of the data structure in which the shared secret keys are kept in.  Default 4m.  In
              bytes or use m(mega), k(kilo), g(giga).  The shared secret cache is used when  a  same  client  is
              making multiple queries using the same public key. It saves a substantial amount of CPU.

       dnscrypt-shared-secret-cache-slabs: <number>
              Give  power  of  2  number of slabs, this is used to reduce lock contention in the dnscrypt shared
              secrets cache.  Close to the number of cpus is a fairly good setting.

       dnscrypt-nonce-cache-size: <memory size>
              Give the size of the data structure in which the client nonces are kept in.  Default 4m. In  bytes
              or  use m(mega), k(kilo), g(giga).  The nonce cache is used to prevent dnscrypt message replaying.
              Client nonce should be unique for any pair of client pk/server sk.

       dnscrypt-nonce-cache-slabs: <number>
              Give power of 2 number of slabs, this is used to reduce lock  contention  in  the  dnscrypt  nonce
              cache.  Close to the number of cpus is a fairly good setting.

   EDNS Client Subnet Module Options
       The ECS module must be configured in the module-config: "subnetcache validator iterator" directive and be
       compiled into the daemon to be enabled.  These settings go in the server: section.

       If the destination address is whitelisted with Unbound will add the EDNS0 option to the query  containing
       the  relevant  part  of the client's address. When an answer contains the ECS option the response and the
       option are placed in a specialized cache. If the authority indicated no support, the response  is  stored
       in the regular cache.

       Additionally,  when  a  client includes the option in its queries, Unbound will forward the option to the
       authority if present in the whitelist, or client-subnet-always-forward is set to yes. In  this  case  the
       lookup in the regular cache is skipped.

       The  maximum size of the ECS cache is controlled by 'msg-cache-size' in the configuration file. On top of
       that, for each query only 100 different subnets are  allowed  to  be  stored  for  each  address  family.
       Exceeding that number, older entries will be purged from cache.

       send-client-subnet: <IP address>
              Send  client  source  address  to  this  authority. Append /num to indicate a classless delegation
              netblock, for example like 10.2.3.4/24 or 2001::11/64. Can be given  multiple  times.  Authorities
              not  listed  will  not  receive  edns-subnet  information,  unless domain in query is specified in
              client-subnet-zone.

       client-subnet-zone: <domain>
              Send client source address in queries for this domain and its subdomains. Can  be  given  multiple
              times.  Zones  not  listed  will  not  receive edns-subnet information, unless hosted by authority
              specified in send-client-subnet.

       client-subnet-always-forward: <yes or no>
              Specify whether the ECS whitelist check (configured using send-client-subnet) is applied  for  all
              queries,  even  if  the triggering query contains an ECS record, or only for queries for which the
              ECS record is generated using the querier address (and therefore did not contain ECS data  in  the
              client  query).  If  enabled, the whitelist check is skipped when the client query contains an ECS
              record. Default is no.

       max-client-subnet-ipv6: <number>
              Specifies the maximum prefix length of the client source address we are willing to expose to third
              parties for IPv6.  Defaults to 56.

       max-client-subnet-ipv4: <number>
              Specifies the maximum prefix length of the client source address we are willing to expose to third
              parties for IPv4. Defaults to 24.

       min-client-subnet-ipv6: <number>
              Specifies the minimum prefix length of the IPv6 source mask we are willing to accept  in  queries.
              Shorter source masks result in REFUSED answers. Source mask of 0 is always accepted. Default is 0.

       min-client-subnet-ipv4: <number>
              Specifies  the  minimum prefix length of the IPv4 source mask we are willing to accept in queries.
              Shorter source masks result in REFUSED answers. Source mask of 0 is always accepted. Default is 0.

       max-ecs-tree-size-ipv4: <number>
              Specifies the maximum number of subnets ECS answers kept in  the  ECS  radix  tree.   This  number
              applies for each qname/qclass/qtype tuple. Defaults to 100.

       max-ecs-tree-size-ipv6: <number>
              Specifies  the  maximum  number  of  subnets  ECS answers kept in the ECS radix tree.  This number
              applies for each qname/qclass/qtype tuple. Defaults to 100.

   Opportunistic IPsec Support Module Options
       The IPsec module must be configured in the module-config: "ipsecmod validator iterator" directive and  be
       compiled into the daemon to be enabled.  These settings go in the server: section.

       When unbound receives an A/AAAA query that is not in the cache and finds a valid answer, it will withhold
       returning the answer and instead will generate an IPSECKEY subquery for the  same  domain  name.   If  an
       answer was found, unbound will call an external hook passing the following arguments:

            QNAME
                 Domain name of the A/AAAA and IPSECKEY query.  In string format.

            IPSECKEY TTL
                 TTL of the IPSECKEY RRset.

            A/AAAA
                 String  of  space  separated IP addresses present in the A/AAAA RRset.  The IP addresses are in
                 string format.

            IPSECKEY
                 String of space separated IPSECKEY RDATA present in the IPSECKEY RRset.  The IPSECKEY RDATA are
                 in DNS presentation format.

       The  A/AAAA  answer  is  then cached and returned to the client.  If the external hook was called the TTL
       changes to ensure it doesn't surpass ipsecmod-max-ttl.

       The same procedure is also followed when prefetch: is used, but the A/AAAA answer is given to the  client
       before  the  hook  is  called.  ipsecmod-max-ttl ensures that the A/AAAA answer given from cache is still
       relevant for opportunistic IPsec.

       ipsecmod-enabled: <yes or no>
              Specifies whether the IPsec module is enabled or not.  The IPsec module still needs to be  defined
              in  the  module-config:  directive.   This  option  facilitates  turning on/off the module without
              restarting/reloading unbound.  Defaults to yes.

       ipsecmod-hook: <filename>
              Specifies the external hook that unbound will call with system(3).  The file can be  specified  as
              an absolute/relative path.  The file needs the proper permissions to be able to be executed by the
              same user that runs unbound.  It must  be  present  when  the  IPsec  module  is  defined  in  the
              module-config: directive.

       ipsecmod-strict: <yes or no>
              If  enabled  unbound  requires the external hook to return a success value of 0.  Failing to do so
              unbound will reply with SERVFAIL.  The A/AAAA answer will also not be cached.  Defaults to no.

       ipsecmod-max-ttl: <seconds>
              Time to live maximum for A/AAAA cached records after calling the external hook.  Defaults to 3600.

       ipsecmod-ignore-bogus: <yes or no>
              Specifies the behaviour of unbound when the IPSECKEY answer is bogus.  If set  to  yes,  the  hook
              will  be called and the A/AAAA answer will be returned to the client.  If set to no, the hook will
              not be called and the answer to the A/AAAA query will  be  SERVFAIL.   Mainly  used  for  testing.
              Defaults to no.

       ipsecmod-whitelist: <domain>
              Whitelist  the domain so that the module logic will be executed.  Can be given multiple times, for
              different domains.  If the option is not specified, all domains are treated as  being  whitelisted
              (default).

   Cache DB Module Options
       The  Cache  DB module must be configured in the module-config: "validator cachedb iterator" directive and
       be compiled into the daemon with --enable-cachedb.   If  this  module  is  enabled  and  configured,  the
       specified  backend  database works as a second level cache: When Unbound cannot find an answer to a query
       in its built-in in-memory cache, it consults the specified backend.  If it finds a valid  answer  in  the
       backend, Unbound uses it to respond to the query without performing iterative DNS resolution.  If Unbound
       cannot even find an answer in the backend, it resolves the query as usual, and stores the answer  in  the
       backend.

       If  Unbound  was built with --with-libhiredis on a system that has installed the hiredis C client library
       of Redis, then the "redis" backend can be used.  This  backend  communicates  with  the  specified  Redis
       server  over  a  TCP  connection to store and retrieve cache data.  It can be used as a persistent and/or
       shared cache backend.  It should be noted that Unbound never removes data stored  in  the  Redis  server,
       even  if  some  data  have  expired  in terms of DNS TTL or the Redis server has cached too much data; if
       necessary the Redis server must be configured to limit the cache  size,  preferably  with  some  kind  of
       least-recently-used  eviction  policy.  This backend uses synchronous communication with the Redis server
       based on the assumption that the communication is stable and sufficiently fast.  The thread waiting for a
       response  from the Redis server cannot handle other DNS queries.  Although the backend has the ability to
       reconnect to the server when the connection is closed unexpectedly and there is a configurable timeout in
       case the server is overly slow or hangs up, these cases are assumed to be very rare.  If connection close
       or timeout happens too often,  Unbound  will  be  effectively  unusable  with  this  backend.   It's  the
       administrator's responsibility to make the assumption hold.

       The cachedb: clause gives custom settings of the cache DB module.

       backend: <backend name>
              Specify  the  backend  database  name.   The  default  database  is  the  in-memory  backend named
              "testframe", which, as the name suggests, is not of any practical use.  Depending  on  the  build-
              time configuration, "redis" backend may also be used as described above.

       secret-seed: <"secret string">
              Specify  a  seed to calculate a hash value from query information.  This value will be used as the
              key of the corresponding answer for the backend database and can be customized if the hash  should
              not  be  predictable  operationally.   If  the  backend  database  is  shared  by multiple Unbound
              instances, all instances must use the same secret seed.  This option defaults to "default".

       The following cachedb otions are specific to the redis backend.

       redis-server-host: <server address or name>
              The IP (either v6 or v4) address or domain name of the Redis server.  In  general  an  IP  address
              should be specified as otherwise Unbound will have to resolve the name of the server every time it
              establishes a connection to the server.  This option defaults to "127.0.0.1".

       redis-server-port: <port number>
              The TCP port number of the Redis server.  This option defaults to 6379.

       redis-timeout: <msec>
              The period until when Unbound waits for a response from the Redis sever.  If this timeout  expires
              Unbound  closes the connection, treats it as if the Redis server does not have the requested data,
              and will try to re-establish a new connection later.  This option defaults to 100 milliseconds.

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

       /etc/unbound
              default unbound working directory.

       default
              chroot(2) location.

       /etc/unbound/unbound.conf
              unbound configuration file.

       /run/unbound.pid
              default unbound pidfile with process ID of the running daemon.

       unbound.log
              unbound log file. default is to log to syslog(3).

SEE ALSO

       unbound(8), unbound-checkconf(8).

AUTHORS

       Unbound was written by NLnet Labs. Please see CREDITS file in the distribution for further details.