unbound.conf(5)                  unbound 1.8.1                 unbound.conf(5)



NAME
       unbound.conf - Unbound configuration file.

SYNOPSIS
       unbound.conf

DESCRIPTION
       unbound.conf  is  used  to  configure  unbound(8).  The file format has
       attributes and values. Some attributes  have  attributes  inside  them.
       The notation is: attribute: value.

       Comments  start  with  #  and  last to the end of line. Empty lines are
       ignored as is whitespace at the beginning of a line.

       The utility unbound-checkconf(8) can  be  used  to  check  unbound.conf
       prior to usage.

EXAMPLE
       An    example    config   file   is   shown   below.   Copy   this   to
       /etc/unbound/unbound.conf and start the server with:

            $ unbound -c /etc/unbound/unbound.conf

       Most settings are the defaults. Stop the server with:

            $ kill `cat /etc/unbound/unbound.pid`

       Below is a minimal config file. The  source  distribution  contains  an
       extensive example.conf file with all the options.

       # unbound.conf(5) config file for unbound(8).
       server:
            directory: "/etc/unbound"
            username: unbound
            # make sure unbound can access entropy from inside the chroot.
            # e.g. on linux the use these commands (on BSD, devfs(8) is used):
            #      mount --bind -n /dev/random /etc/unbound/dev/random
            # and  mount --bind -n /dev/log /etc/unbound/dev/log
            chroot: "/etc/unbound"
            # logfile: "/etc/unbound/unbound.log"  #uncomment to use logfile.
            pidfile: "/etc/unbound/unbound.pid"
            # verbosity: 1      # uncomment and increase to get more logging.
            # listen on all interfaces, answer queries from the local subnet.
            interface: 0.0.0.0
            interface: ::0
            access-control: 10.0.0.0/8 allow
            access-control: 2001:DB8::/64 allow

FILE FORMAT
       There  must be whitespace between keywords. Attribute keywords end with
       a colon ':'.  An attribute is followed by its containing attributes, or
       a value.

       Files  can be included using the include: directive. It can appear any-
       where, it accepts a single file name as argument.  Processing continues
       as  if  the text from the included file was copied into the config file
       at that point.  If also using chroot, using full  path  names  for  the
       included files works, relative pathnames for the included names work if
       the directory where the daemon is  started  equals  its  chroot/working
       directory  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 command-
              line, see unbound(8).

       statistics-interval: <seconds>
              The number of seconds between printing statistics to the log for
              every  thread.  Disable with value 0 or "". Default is disabled.
              The histogram statistics are only printed if replies  were  sent
              during  the  statistics  interval,  requestlist  statistics  are
              printed for every interval (but can be 0).  This is because  the
              median calculation requires data to be present.

       statistics-cumulative: <yes or no>
              If  enabled,  statistics  are cumulative since starting unbound,
              without clearing the statistics counters after logging the  sta-
              tistics. Default is no.

       extended-statistics: <yes or no>
              If  enabled,  extended  statistics are printed from unbound-con-
              trol(8).  Default is off, because keeping track of more  statis-
              tics takes time.  The counters are listed in unbound-control(8).

       num-threads: <number>
              The  number  of threads to create to serve clients. Use 1 for no
              threading.

       port: <port number>
              The port number, default 53, on which  the  server  responds  to
              queries.

       interface: <ip address[@port]>
              Interface  to  use  to connect to the network. This interface is
              listened to for queries from clients, and answers to clients are
              given  from  it.  Can be given multiple times to work on several
              interfaces. If none are given the default is to listen to local-
              host.   The  interfaces  are not changed on a reload (kill -HUP)
              but only on restart.  A port number can be specified with  @port
              (without spaces between interface and port number), if not spec-
              ified the default port (from port) is used.

       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  inter-
              faces.  If  none  are  given  the default (all) is used. You can
              specify the same interfaces in  interface:  and  outgoing-inter-
              face:  lines,  the  interfaces  are then used for both purposes.
              Outgoing queries are sent via a  random  outgoing  interface  to
              counter spoofing.

              If  an  IPv6 netblock is specified instead of an individual IPv6
              address, outgoing UDP  queries  will  use  a  randomised  source
              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 pre-
              fer-ip6: yes to increase  the  likelihood  of  IPv6  nameservers
              being  selected  for  queries.  On Linux you need these two com-
              mands to be able to use the freebind socket  option  to  receive
              traffic  for  the ip6 netblock: ip -6 addr add mynetblock/64 dev
              lo && ip -6 route add local mynetblock/64 dev lo

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

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

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

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

       outgoing-num-tcp: <number>
              Number of outgoing TCP buffers to allocate per  thread.  Default
              is  10.  If  set  to  0, or if do-tcp is "no", no TCP queries to
              authoritative  servers  are  done.   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  fragmen-
              tation  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.

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

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

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

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

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

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

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

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

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

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

       ip-freebind: <yes or no>
              If yes, then use IP_FREEBIND  socket  option  on  sockets  where
              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  kilo-
              bytes, megabytes or gigabytes (1024*1024 bytes in a megabyte).

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

       cache-max-ttl: <seconds>
              Time to live maximum for  RRsets  and  messages  in  the  cache.
              Default  is  86400  seconds  (1  day).  If the maximum kicks in,
              responses to clients still get decrementing TTLs  based  on  the
              original  (larger)  values.   When the internal TTL expires, the
              cache item has expired.  Can be set lower to force the  resolver
              to query for data often, and not trust (very large) TTL values.

       cache-min-ttl: <seconds>
              Time  to  live  minimum  for  RRsets  and messages in the cache.
              Default is 0.  If the 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 con-
              tains roundtrip timing, lameness and EDNS  support  information.
              Default is 900.

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

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

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

       define-tag: <"list of tags">
              Define the tags that can be used with local-zone and access-con-
              trol.   Enclose  the  list  between  quotes  ("") and put spaces
              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 config-
              ured,  the  option value used is progressively reduced, first to
              1% of the configured value, then to 0.2% of the configured value
              if  the number of free buffers falls below 35% of the total num-
              ber configured, and finally to 0 if the number of  free  buffers
              falls  below 20% of the total number configured. A minimum time-
              out of 200 milliseconds is observed  regardless  of  the  option
              value used.

       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 con-
              figured 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 regard-
              less 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.

       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 provider TLS service on its TCP  sockets.
              The clients have to use tls-upstream: yes.  The file is the pri-
              vate key for the TLS session.  The public certificate is in  the
              tls-service-pem  file.   Default  is "", turned off.  Requires a
              restart (a reload is not enough) if changed, because the private
              key  is  read  while root permissions are held and before chroot
              (if any).  Normal DNS TCP service  is  not  provided  and  gives
              errors,  this  service is best run with a different port: config
              or @port suffixes in the interface config.

       ssl-service-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 bun-
              dle file, for example "/etc/pki/tls/certs/ca-bundle.crt".  These
              certificates  are  used  for  authenticating connections made to
              outside peers.  For example auth-zone urls, and  also  DNS  over
              TLS connections.

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

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

       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.

       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 action deny stops queries from hosts from that netblock.

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

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

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

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

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

       access-control-tag: <IP netblock> <"list of tags">
              Assign  tags  to  access-control  elements.  Clients  using this
              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  por-
              tion.

              The  pidfile can be either a relative path to the working direc-
              tory, or an absolute path relative to the original root.  It  is
              written  just  prior  to  chroot  and dropping permissions. This
              allows the pidfile to be /var/run/unbound.pid and the chroot  to
              be /var/unbound, for example.

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

              If given a chroot is done to the  given  directory.  By  default
              chroot  is  enabled and the default is "/usr/local/etc/unbound".
              If you give "" no chroot is performed.

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

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

       directory: <directory>
              Sets  the  working  directory  for  the  program.   Default   is
              "/usr/local/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 state-
              ments then those includes can be relative to the working  direc-
              tory.

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

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

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

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

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

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

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

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

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

       root-hints: <filename>
              Read  the  root  hints from this file. Default is nothing, using
              builtin hints for the IN class. The file has the format of  zone
              files,  with  root  nameserver  names  and  addresses  only. The
              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 num-
              bers.  The default is "3 2 1 0 0". Setting all zeroes, "0 0 0  0
              0"  gives  behaviour closer to that of BIND 9, while setting "-1
              -1 -1 -1 -1" gives behaviour rumoured to be closer  to  that  of
              BIND 8.

       harden-short-bufsize: <yes or no>
              Very  small  EDNS buffer sizes from queries are ignored. Default
              is off, since it is legal  protocol  wise  to  send  these,  and
              unbound tries to give very small answers to these queries, where
              possible.

       harden-large-queries: <yes or no>
              Very large queries are ignored. Default  is  off,  since  it  is
              legal  protocol  wise  to send these, and could be necessary for
              operation if TSIG or EDNS payload is very large.

       harden-glue: <yes or no>
              Will trust glue only if it  is  within  the  servers  authority.
              Default is on.

       harden-dnssec-stripped: <yes or no>
              Require  DNSSEC  data  for trust-anchored zones, if such data is
              absent, the zone becomes bogus. If turned  off,  and  no  DNSSEC
              data  is  received  (or the DNSKEY data fails to validate), then
              the zone is made insecure, this behaves like there is  no  trust
              anchor.  You  could turn this off if you are sometimes behind an
              intrusive firewall (of some sort) that removes DNSSEC data  from
              packets,  or  a  zone  changes  from signed to unsigned to badly
              signed often. If turned off you run  the  risk  of  a  downgrade
              attack that disables security for a zone. Default is on.

       harden-below-nxdomain: <yes or no>
              From  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 man-
              dates 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 vali-
              dation  on  nameserver NS sets and the nameserver addresses that
              are encountered on the referral path to the answer.  Default no,
              because  it  burdens  the  authority  servers, and it is not RFC
              standard, and could lead to performance problems because of  the
              extra  query  load  that is generated.  Experimental option.  If
              you enable it  consider  adding  more  numbers  after  the  tar-
              get-fetch-policy to increase the max depth that is checked to.

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

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

       caps-whitelist: <domain>
              Whitelist the domain so that it  does  not  receive  caps-for-id
              perturbed  queries.   For  domains  that do not support 0x20 and
              also fail with fallback  because  they  keep  sending  different
              answers, like some load balancers.  Can be given multiple times,
              for different domains.

       qname-minimisation: <yes or no>
              Send minimum  amount  of  information  to  upstream  servers  to
              enhance privacy.  Only sent minimum required labels of the QNAME
              and set QTYPE to 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 NXDO-
              MAIN and other denials, using information  from  previous  NXDO-
              MAINs  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  addi-
              tional  names  using  private-domain.   No private addresses are
              enabled by default.  We consider to enable this for the  RFC1918
              private  IP  address  space  by  default in later releases. That
              would enable  private  addresses  for  10.0.0.0/8  172.16.0.0/12
              192.168.0.0/16  169.254.0.0/16 fd00::/8 and fe80::/10, since the
              RFC standards say these addresses should not be visible  on  the
              public internet.  Turning on 127.0.0.0/8 would hinder many spam-
              blocklists  as  they  use  that.   Adding  ::ffff:0:0/96   stops
              IPv4-mapped IPv6 addresses from bypassing the filter.

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

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

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

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

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

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

       rrset-roundrobin: <yes or no>
              If yes, Unbound rotates RRSet order in response (the random num-
              ber  is  taken  from the query ID, for speed and thread safety).
              Default is no.

       minimal-responses: <yes or no>
              If yes, Unbound  doesn't  insert  authority/additional  sections
              into  response  messages  when  those sections are not required.
              This reduces response size  significantly,  and  may  avoid  TCP
              fallback  for  some responses.  This may cause a slight speedup.
              The default is yes, even though the DNS  protocol  RFCs  mandate
              these  sections,  and the additional content could be of use and
              save roundtrips for clients.  Because they are not used, and the
              saved  roundtrips are easier saved with prefetch, whilst this is
              faster.

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

       module-config: <"module names">
              Module  configuration,  a list of module names separated by spa-
              ces, surround the string with quotes (""). The  modules  can  be
              validator,  iterator.  Setting this to "iterator" will result in
              a non-validating server.  Setting this to  "validator  iterator"
              will  turn on DNSSEC validation.  The ordering of the modules is
              important.  You must also set trust-anchors for validation to be
              useful.

       trust-anchor-file: <filename>
              File  with  trusted  keys  for  validation.  Both  DS and DNSKEY
              entries can appear in the file. The format of the  file  is  the
              standard  DNS  Zone  file  format.   Default  is "", or no trust
              anchor file.

       auto-trust-anchor-file: <filename>
              File with trust anchor for  one  zone,  which  is  tracked  with
              RFC5011  probes.   The  probes are several times per month, thus
              the machine must be online frequently.  The initial file can  be
              one  with  contents as described in trust-anchor-file.  The file
              is written to when the anchor is updated, so  the  unbound  user
              must  have  write permission.  Write permission to the file, but
              also to the directory it is in  (to  create  a  temporary  file,
              which is necessary to deal with filesystem full events), 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 addi-
              tion to the trust-anchor-files.  The resource record is  entered
              in  the  same  format  as 'dig' or 'drill' prints them, the same
              format as in the zone file. Has to be on a single line, with  ""
              around it. A TTL can be specified for ease of cut and paste, but
              is ignored.  A class can be specified, but class IN is default.

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

       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 par-
              ent 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 ver-
              ifying RRSIG inception and expiration dates, instead of the cur-
              rent date. Do not set this unless you  are  debugging  signature
              inception  and  expiration.  The value -1 ignores the date alto-
              gether, useful for some special applications.

       val-sig-skew-min: <seconds>
              Minimum number of seconds of clock skew to  apply  to  validated
              signatures.   A  value of 10% of the signature lifetime (expira-
              tion - inception) is used, capped by this setting.   Default  is
              3600  (1  hour)  which  allows for daylight savings differences.
              Lower this value for more strict checking of short lived  signa-
              tures.

       val-sig-skew-max: <seconds>
              Maximum  number  of  seconds of clock skew to apply to validated
              signatures.  A value of 10% of the signature  lifetime  (expira-
              tion  -  inception) is used, capped by this setting.  Default is
              86400 (24 hours) which allows for timezone setting  problems  in
              stable  domains.  Setting both min and max very low disables the
              clock skew allowances.  Setting both min and max very high makes
              the validator check the signature timestamps less strictly.

       val-bogus-ttl: <number>
              The  time  to  live for bogus data. This is data that has failed
              validation; due to invalid signatures or other checks.  The  TTL
              from  that  data  cannot  be  trusted,  and  this  value is used
              instead. The value is in seconds, default 60.  The time interval
              prevents repeated revalidation of bogus data.

       val-clean-additional: <yes or no>
              Instruct  the  validator to remove data from the additional sec-
              tion of secure messages that are not signed  properly.  Messages
              that  are  insecure,  bogus,  indeterminate or unchecked are not
              affected. Default is yes. Use this setting to protect the  users
              that  rely on this validator for authentication from 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  Dis-
              abled)  flag does not disable checking any more.  This is useful
              if legacy (w2008) servers that set the CD flag but cannot  vali-
              date  DNSSEC  themselves  are the clients, and then unbound pro-
              vides them with DNSSEC protection.  The default value is "no".

       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  kilo-
              bytes, megabytes or gigabytes (1024*1024 bytes in a megabyte).

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

       neg-cache-size: <number>
              Number  of  bytes size of the aggressive negative cache. Default
              is 1 megabyte.  A plain number is in bytes, append 'k',  'm'  or
              'g'  for kilobytes, megabytes or gigabytes (1024*1024 bytes in a
              megabyte).

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

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

       local-zone: <zone> <type>
              Configure  a  local zone. The type determines the answer to give
              if there is no  match  from  local-data.  The  types  are  deny,
              refuse,  static, transparent, redirect, nodefault, typetranspar-
              ent,  inform,  inform_deny,  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.exam-
                 ple.com and www.foo.example.com are redirected, so that users
                 with web browsers  cannot  access  sites  with  suffix  exam-
                 ple.com.

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

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

            always_transparent
                 Like  transparent,  but  ignores local data and resolves nor-
                 mally.

            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 'node-
                 fault' 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  trans-
                 parent.

       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 con-
       tents.

            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 deter-
            mines further processing. If local-data is configured that is  not
            a  subdomain  of a local-zone, a transparent local-zone is config-
            ured.  For record types such as TXT,  use  single  quotes,  as  in
            local-data: 'example. TXT "text"'.

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

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

       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.

       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 rate-
            limited  by  this setting.  The zone of the query is determined by
            examining the nameservers for it, the zone name is  used  to  keep
            track  of  the rate.  For example, 1000 may be a suitable value to
            stop the server from being overloaded with random names, and keeps
            unbound from sending traffic to the nameservers for those zones.

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

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

       ratelimit-factor: <number>
            Set the amount  of  queries  to  rate  limit  when  the  limit  is
            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 mit-
            igating 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 differ-
            ent settings in different parts of  the  namespace.   The  closest
            matching  suffix is used to determine the qps limit.  The rate for
            the  exact  matching  domain  name  is  not  changed,  use   rate-
            limit-for-domain to set that, you might want to use different set-
            tings for a top-level-domain and subdomains.  A value  of  0  will
            disable ratelimiting for domain names that end in this name.

       ip-ratelimit: <number or 0>
            Enable global ratelimiting of queries accepted per ip address.  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 amplifica-
            tion 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  con-
            tention in the ip ratelimit tracking data structure.  Close to the
            number of cpus is a fairly good setting.

       ip-ratelimit-factor: <number>
            Set the amount  of  queries  to  rate  limit  when  the  limit  is
            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.

       low-rtt: <msec time>
            Set the time in millisecond that is considere a low ping time  for
            fast  server  selection with the low-rtt-permil option, that turns
            this on or off.  The default is 45 msec, a number from IPv6  quick
            response documents.

       low-rtt-permil: <number>
            Specify  how  many  times out of 1000 to pick the fast server from
            the low rtt band.  0 turns the feature off.  A value of 900  would
            pick  the fast server when such fast servers are available 90 per-
            cent of the time, and the remaining  time  perform  normal  explo-
            ration   of   random   servers.   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 low-rtt option can  be  used  to  specify
            which servers are picked for fast server selection, servers with a
            ping roundtrip time below that value are considered.  The  default
            for low-rtt-permil is 0.

   Remote Control Options
       In  the remote-control: clause are the declarations for the remote con-
       trol facility.  If this is enabled, the unbound-control(8) utility  can
       be  used  to  send  commands to the running unbound server.  The server
       uses these clauses to setup TLSv1 security  for  the  connection.   The
       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  per-
            missions on the file to the user and group that is configured, the
            access bits are set to allow the group members to access the  con-
            trol 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-con-
            trol-setup utility.  This file is used by the unbound server,  and
            also by unbound-control.

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

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

   Stub Zone Options
       There may be multiple stub-zone: clauses. Each with a name: and zero or
       more  hostnames  or IP addresses.  For the stub zone this list of name-
       servers is used. Class IN is assumed.  The servers should be  authority
       servers,  not  recursors;  unbound  performs  the  recursive processing
       itself for stub zones.

       The stub zone can be used to configure authoritative data to be used by
       the resolver that cannot be accessed using the public internet servers.
       This is useful for  company-local  data  or  private  zones.  Setup  an
       authoritative  server  on a different host (or different port). Enter a
       config entry for unbound with stub-addr: <ip address  of  host[@port]>.
       The unbound resolver can then access the data, without referring to the
       public internet for it.

       This setup allows DNSSEC signed zones to be served by  that  authorita-
       tive  server, in which case a trusted key entry with the public key can
       be put in config, so that unbound can validate the data and set the  AD
       bit  on  replies for the private zone (authoritative servers do not set
       the AD bit).  This setup makes unbound capable of answering queries for
       the private zone, and can even set the AD bit ('authentic'), but the AA
       ('authoritative') bit is not set on these replies.

       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.   The  cert name match code needs OpenSSL 1.1.0
              or later to be enabled.

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

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

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

       forward-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.

       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.

       url: <url to zonefile>
              Where to download a zonefile for the zone.  With http or  https.
              An   example   for   the  url  is  "http://www.example.com/exam-
              ple.org.zone".  Multiple url statements can be given,  they  are
              tried  in turn.  If only urls are given the SOA refresh timer is
              used to wait for making new  downloads.   If  also  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 noti-
              fies.  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. 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 behav-
              iour  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 dis-
              abled 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).

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

       python-script: <python file>
              The script file to load.

   DNS64 Module Options
       The dns64 module must be configured in the module-config:  "dns64  val-
       idator  iterator"  directive  and  be  compiled  into  the daemon to be
       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 mul-
              tiple  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/pub-
       lic  keys cannot be generated by unbound.  You can use dnscrypt-wrapper
       to generate those:  https://github.com/cofyc/dnscrypt-wrapper/blob/mas-
       ter/README.md#usage

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

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

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

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

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

       dnscrypt-provider-cert-rotated: <path to cert file>
              Path to a certificate that we should be able to  serve  existing
              connection   from   but   do   not   want   to   advertise  over
              dnscrypt-provider's TXT record certs  distribution.   A  typical
              use  case  is  when  rotating certificates, existing clients may
              still use the client magic from the old cert  in  their  queries
              until  they  fetch  and  update the new cert. Likewise, it would
              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 differ-
       ent 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. Author-
              ities 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.

   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 fol-
       lowing arguments:

            QNAME
                 Domain name of the A/AAAA and IPSECKEY query.  In string for-
                 mat.

            IPSECKEY TTL
                 TTL of the IPSECKEY RRset.

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

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

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

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

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

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

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

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

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

       ipsecmod-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 speci-
       fied backend database works as a second level cache: When Unbound  can-
       not  find an answer to a query in its built-in in-memory cache, it con-
       sults the specified backend.  If it finds a valid answer in  the  back-
       end,  Unbound uses it to respond to the query without performing itera-
       tive 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" back-
       end 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 sta-
       ble  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  effec-
       tively  unusable with this backend.  It's the administrator's responsi-
       bility to make the assumption hold.

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

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

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

       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  other-
              wise  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 connec-
              tion, 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 ser-
       vice  levels are lower, notable very large data and a high TCP load are
       no longer supported. Very large data and high TCP loads are exceptional
       for the DNS.  DNSSEC validation is enabled, just add trust anchors.  If
       you do not have to worry about programs using more than 3 Mb of memory,
       the below example is not for you. Use the defaults to receive full ser-
       vice, which on BSD-32bit tops out at 30-40 Mb after heavy usage.

       # example settings that reduce memory usage
       server:
            num-threads: 1
            outgoing-num-tcp: 1 # this limits TCP service, uses less buffers.
            incoming-num-tcp: 1
            outgoing-range: 60  # uses less memory, but less performance.
            msg-buffer-size: 8192   # note this limits service, 'no huge stuff'.
            msg-cache-size: 100k
            msg-cache-slabs: 1
            rrset-cache-size: 100k
            rrset-cache-slabs: 1
            infra-cache-numhosts: 200
            infra-cache-slabs: 1
            key-cache-size: 100k
            key-cache-slabs: 1
            neg-cache-size: 10k
            num-queries-per-thread: 30
            target-fetch-policy: "2 1 0 0 0 0"
            harden-large-queries: "yes"
            harden-short-bufsize: "yes"

FILES
       /usr/local/etc/unbound
              default unbound working directory.

       /usr/local/etc/unbound
              default chroot(2) location.

       /usr/local/etc/unbound/unbound.conf
              unbound configuration file.

       /usr/local/etc/unbound/unbound.pid
              default unbound pidfile with process ID of the running daemon.

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

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

AUTHORS
       Unbound was written by NLnet Labs. Please see CREDITS file in the  dis-
       tribution for further details.



NLnet Labs                       Oct  8, 2018                  unbound.conf(5)