unbound.conf(5)                 unbound 1.13.2                 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 at-
       tributes 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 ig-
       nored 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/un-
       bound.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 ex-
       tensive 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/urandom /etc/unbound/dev/urandom
            # and  mount --bind -n /dev/log /etc/unbound/dev/log
            chroot: "/etc/unbound"
            # logfile: "/etc/unbound/unbound.log"  #uncomment to use logfile.
            pidfile: "/etc/unbound/unbound.pid"
            # verbosity: 1      # uncomment and increase to get more logging.
            # listen on all interfaces, answer queries from the local subnet.
            interface: 0.0.0.0
            interface: ::0
            access-control: 10.0.0.0/8 allow
            access-control: 2001:DB8::/64 allow

FILE FORMAT
       There must be whitespace between keywords.  Attribute keywords end with
       a colon ':'.  An attribute is followed by a value,  or  its  containing
       attributes in which case it is referred to as a clause.  Clauses can be
       repeated throughout the file (or included files)  to  group  attributes
       under the same clause.

       Files  can be included using the include: directive. It can appear 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 in-
       cluded  files  works, relative pathnames for the included names work if
       the directory where the daemon is started equals its chroot/working di-
       rectory  or  is  specified before the include statement with directory:
       dir.  Wildcards can be used to include multiple files, see glob(7).

       For a more structural include option, the  include-toplevel:  directive
       can  be used.  This closes whatever clause is currently active (if any)
       and forces the use of clauses in the included  files  and  right  after
       this directive.

   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  including short information per query.
              Level 3 gives query level information, output per query.   Level
              4  gives algorithm level information.  Level 5 logs client iden-
              tification for cache misses.  Default is level 1.  The verbosity
              can also be increased from the commandline, see unbound(8).

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

       statistics-cumulative: <yes or no>
              If enabled, statistics are cumulative  since  starting  unbound,
              without  clearing the statistics counters after logging the 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.  If an interface name is used instead of  an  ip  address,
              the list of ip addresses on that interface are used.  The inter-
              faces are not changed on  a  reload  (kill  -HUP)  but  only  on
              restart.   A  port  number  can be specified with @port (without
              spaces between interface and port number), if not specified  the
              default port (from port) is used.

       ip-address: <ip address[@port]>
              Same as interface: (for ease of compatibility with nsd.conf).

       interface-automatic: <yes or no>
              Listen  on all addresses on all (current and future) interfaces,
              detect the source interface on UDP  queries  and  copy  them  to
              replies.   This  is  a  lot like ip-transparent, but this option
              services all interfaces whilst with ip-transparent you  can  se-
              lect  which  (future)  interfaces  unbound  provides service on.
              This feature is experimental, and needs support in your  OS  for
              particular socket options.  Default value is no.

       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 ad-
              dress taken from the netblock to counter spoofing. Requires  the
              IPv6  netblock to be routed to the host running unbound, and re-
              quires 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 be-
              ing selected for queries.  On Linux you need these two  commands
              to  be able to use the freebind socket option to receive traffic
              for the ip6 netblock: ip -6 addr add mynetblock/64 dev lo &&  ip
              -6 route add local mynetblock/64 dev lo

       outgoing-range: <number>
              Number  of ports to open. This number of file descriptors can be
              opened per thread. Must be at least 1. Default depends  on  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  in-
              creases  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  au-
              thoritative servers are done.  For larger installations increas-
              ing 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.  De-
              fault  is  1232  which  is the DNS Flag Day 2020 recommendation.
              Setting to 512 bypasses even the most stringent path  MTU  prob-
              lems,  but  is seen as extreme, since the amount of TCP fallback
              generated is excessive (probably also for  this  resolver,  con-
              sider tuning the outgoing tcp number).

       max-udp-size: <number>
              Maximum  UDP response size (not applied to TCP response).  65536
              disables the udp response size maximum, and uses the choice from
              the  client,  always.  Suggested values are 512 to 4096. Default
              is 4096.

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

       msg-buffer-size: <number>
              Number of bytes size of the message buffers.  Default  is  65552
              bytes,  enough  for 64 Kb packets, the maximum DNS message size.
              No message larger than this can be sent or received. Can be  re-
              duced  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 al-
              lowed time.  This protects against denial  of  service  by  slow
              queries or high query rates.  Default 200 milliseconds.  The ef-
              fect 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.

       udp-connect: <yes or no>
              Perform connect for UDP sockets that mitigates ICMP side channel
              leakage.  Default is yes.

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

       so-rcvbuf: <number>
              If  not 0, then set the SO_RCVBUF socket option to get more 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:  re-
              source temporarily unavailable' can get logged, the buffer over-
              run is also visible by netstat -su.  Default is  0  (use  system
              value).   Specify  the number of bytes to ask for, try "4m" on a
              very busy server.  The OS caps it at a maximum, on linux unbound
              needs  root permission to bypass the limit, or the admin can use
              sysctl net.core.wmem_max.  On BSD, Solaris changes  are  similar
              to so-rcvbuf.

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

       ip-transparent: <yes or no>
              If  yes,  then use IP_TRANSPARENT socket option on sockets where
              unbound is listening for incoming traffic.  Default no.   Allows
              you  to bind to non-local interfaces.  For example for non-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  un-
              bound 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 avail-
              able.

       ip-dscp: <number>
              The value of the Differentiated Services Codepoint (DSCP) in the
              differentiated services field (DS) of  the  outgoing  IP  packet
              headers.   The  field replaces the outdated IPv4 Type-Of-Service
              field and the IPV6 traffic class field.

       rrset-cache-size: <number>
              Number of bytes size of the RRset cache. Default is 4 megabytes.
              A  plain  number  is  in bytes, append 'k', 'm' or 'g' for 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. De-
              fault is 86400 seconds (1 day).  When the TTL expires, the cache
              item  has  expired.   Can  be set lower to force the resolver to
              query for data often, and not trust  (very  large)  TTL  values.
              Downstream clients also see the lower TTL.

       cache-min-ttl: <seconds>
              Time  to  live minimum for RRsets and messages in the cache. De-
              fault 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.

       infra-keep-probing: <yes or no>
              If enabled the server keeps probing hosts that are down, in  the
              one  probe  at  a  time  regime.  Default is no.  Hosts that are
              down, eg. they did not respond during the one probe  at  a  time
              period,  are  marked as down and it may take infra-host-ttl time
              to get probed again.

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

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

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

       prefer-ip4: <yes or no>
              If enabled, prefer IPv4 transport for sending DNS queries to in-
              ternet  nameservers. Default is no.  Useful if the IPv6 netblock
              the server has, the entire /64 of that is not owned by one oper-
              ator  and  the reputation of the netblock /64 is an issue, using
              IPv4 then uses the IPv4 filters that the upstream servers have.

       prefer-ip6: <yes or no>
              If enabled, prefer IPv6 transport for sending DNS queries to in-
              ternet 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 re-
              sponds 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).   De-
              fault  is system default MSS determined by interface MTU and ne-
              gotiation 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  in-
              terface 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 op-
              tion  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.

       tcp-reuse-timeout: <msec>
              The  period Unbound will keep TCP persistent connections open to
              authority servers. This option defaults to 60000 milliseconds.

       max-reuse-tcp-queries: <number>
              The maximum number of queries that can be sent on  a  persistent
              TCP connection.  This option defaults to 200 queries.

       tcp-auth-query-timeout: <number>
              Timeout  in  milliseconds for TCP queries to auth servers.  This
              option defaults to 3000 milliseconds.

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

       edns-tcp-keepalive-timeout: <msec>
              The period Unbound will wait for a query  on  a  TCP  connection
              when  EDNS  TCP Keepalive is active. If this timeout expires Un-
              bound 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 re-
              duced to 1% of the configured value, then to 0.2% of the config-
              ured  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 mini-
              mum actual timeout of 200 milliseconds is observed regardless of
              the advertised timeout.

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

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

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

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

       tls-service-key: <file>
              If enabled, the server provides DNS-over-TLS  or  DNS-over-HTTPS
              service  on  the  TCP  ports marked implicitly or explicitly for
              these services with tls-port or https-port. The file  must  con-
              tain the private key for the TLS session, the public certificate
              is in the tls-service-pem file and it must also be specified  if
              tls-service-key  is  specified.   The default is "", turned off.
              Enabling or disabling this service requires a restart (a  reload
              is  not  enough), because the key is read while root permissions
              are held and before chroot (if any).  The ports enabled  implic-
              itly  or explicitly via tls-port: and https-port: do not provide
              normal DNS TCP service. Unbound needs to be compiled  with  lib-
              nghttp2 in order to provide DNS-over-HTTPS.

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

       tls-service-pem: <file>
              The  public  key  certificate pem file for the tls service.  De-
              fault 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.  It is read at start up before permission  drop
              and chroot.

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

       tls-win-cert: <yes or no>
              Add  the system certificates to the cert bundle certificates for
              authentication.  If no cert bundle, it uses only these  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.

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

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

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

       pad-responses: <yes or no>
              If enabled, TLS serviced queries that contained an EDNS  Padding
              option  will  cause  responses padded to the closest multiple of
              the size specified in pad-responses-block-size.  Default is yes.

       pad-responses-block-size: <number>
              The block size with which to pad responses  serviced  over  TLS.
              Only  responses  to  padded  queries will be padded.  Default is
              468.

       pad-queries: <yes or no>
              If enabled, all queries sent over TLS upstreams will  be  padded
              to   the   closest   multiple   of   the   size   specified   in
              pad-queries-block-size.  Default is yes.

       pad-queries-block-size: <number>
              The block size with which to  pad  queries  sent  over  TLS  up-
              streams.  Default is 128.

       tls-use-sni: <yes or no>
              Enable  or disable sending the SNI extension on TLS connections.
              Default is yes.  Changing the value requires a reload.

       https-port: <number>
              The port number on which to provide DNS-over-HTTPS service,  de-
              fault  443,  only interfaces configured with that port number as
              @number get the HTTPS service.

       http-endpoint: <endpoint string>
              The HTTP endpoint to provide DNS-over-HTTPS service on.  Default
              "/dns-query".

       http-max-streams: <number of streams>
              Number  used in the SETTINGS_MAX_CONCURRENT_STREAMS parameter in
              the HTTP/2 SETTINGS frame for  DNS-over-HTTPS  connections.  De-
              fault 100.

       http-query-buffer-size: <size in bytes>
              Maximum  number  of bytes used for all HTTP/2 query buffers com-
              bined. These buffers contain (partial) DNS queries  waiting  for
              request  stream completion.  An RST_STREAM frame will be send to
              streams exceeding this limit. Default is 4  megabytes.  A  plain
              number  is  in  bytes,  append  'k',  'm'  or 'g' for kilobytes,
              megabytes or gigabytes (1024*1024 bytes in a megabyte).

       http-response-buffer-size: <size in bytes>
              Maximum number of bytes used for  all  HTTP/2  response  buffers
              combined.  These  buffers  contain  DNS  responses waiting to be
              written back to the clients.  An RST_STREAM frame will  be  send
              to streams exceeding this limit. Default is 4 megabytes. A plain
              number is in bytes,  append  'k',  'm'  or  'g'  for  kilobytes,
              megabytes or gigabytes (1024*1024 bytes in a megabyte).

       http-nodelay: <yes or no>
              Set  TCP_NODELAY  socket  option on sockets used to provide DNS-
              over-HTTPS service.  Ignored if the option is not available. De-
              fault is yes.

       http-notls-downstream: <yes or no>
              Disable use of TLS for the downstream DNS-over-HTTP connections.
              Useful for local back end servers.  Default is no.

       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 ap-
              pended for a classless network block. The action  can  be  deny,
              refuse,   allow,  allow_setrd,  allow_snoop,  deny_non_local  or
              refuse_non_local.  The most specific netblock match is used,  if
              none match deny is used.  The order of the access-control state-
              ments therefore does not matter.

              The action deny stops queries from hosts from that netblock.

              The action refuse stops queries too, but sends a DNS  rcode  RE-
              FUSED 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 do-
              mains  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  ac-
              cess  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 ac-
              cess-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 ac-
              tion is the first tag match between access-control-tag  and  lo-
              cal-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 di-
              rectory, 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  al-
              lows the pidfile to be /var/run/unbound.pid and the chroot to be
              /var/unbound, for example. Note that Unbound is not able to  re-
              move the pidfile after termination when it is located outside of
              the chroot directory.

              Additionally, unbound may need to access /dev/urandom  (for  en-
              tropy) from inside the chroot.

              If given a chroot is done to the given directory. By default ch-
              root 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 re-
              quires privileges, then a reload will fail; a restart is needed.

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

       logfile: <filename>
              If "" is given, logging goes to stderr, or nowhere  once  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 "un-
              bound".   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-tag-queryreply: <yes or no>
              Prints  the  word  'query'  and  'reply'  with  log-queries  and
              log-replies.   This makes filtering logs easier.  The default is
              off (for backwards compatibility).

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

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

       pidfile: <filename>
              The  process  id  is  written  to the file. Default is "/usr/lo-
              cal/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  de-
              fault  may become outdated, when servers change, therefore it is
              good practice to use a root-hints file.

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

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

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

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

       hide-http-user-agent: <yes or no>
              If enabled the HTTP header User-Agent is not set. Use with  cau-
              tion  as  some webserver configurations may reject HTTP requests
              lacking this header.  If needed, it is better to explicitly  set
              the http-user-agent below.

       http-user-agent: <string>
              Set  the  HTTP  User-Agent header for outgoing HTTP requests. If
              set to "", the default, then the package name  and  version  are
              used.

       nsid: <string>
              Add  the  specified  nsid to the EDNS section of the answer when
              queried with an NSID EDNS enabled packet.  As a sequence of  hex
              characters or with ascii_ prefix and then an ascii string.

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

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

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

              Enclose the list between quotes ("") and put spaces between 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 on, as described in the standard.

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

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

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

       harden-below-nxdomain: <yes or no>
              From RFC 8020 (with title "NXDOMAIN: There Really Is Nothing Un-
              derneath"), returns nxdomain to queries for a name below another
              name  that is already known to be nxdomain.  DNSSEC mandates no-
              error for empty nonterminals, hence this is possible.  Very  old
              software might return nxdomain for empty nonterminals (that usu-
              ally happen for reverse IP address lookups), and thus may be in-
              compatible  with  this.  To try to avoid this only DNSSEC-secure
              nxdomains are used, because  the  old  software  does  not  have
              DNSSEC.   Default  is  yes.   The  nxdomain must be secure, this
              means nsec3 with optout is insufficient.

       harden-referral-path: <yes or no>
              Harden the referral path by performing  additional  queries  for
              infrastructure data.  Validates the replies if trust anchors are
              configured and the zones are signed.  This enforces DNSSEC 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  at-
              tempts.   This  perturbs  the  lowercase  and uppercase of query
              names sent to authority servers and checks if  the  reply  still
              has  the  correct casing.  Disabled by default.  This feature is
              an experimental implementation of draft dns-0x20.

       caps-exempt: <domain>
              Exempt the domain so that it does not receive  caps-for-id  per-
              turbed  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 dif-
              ferent domains.

       caps-whitelist: <yes or no>
              Alternate syntax for caps-exempt.

       qname-minimisation: <yes or no>
              Send minimum amount of information to upstream  servers  to  en-
              hance  privacy.   Only send minimum required labels of the QNAME
              and set QTYPE to A when possible.  Best  effort  approach;  full
              QNAME and original QTYPE will be sent when upstream replies with
              a RCODE other than NOERROR, except when receiving NXDOMAIN  from
              a DNSSEC signed zone. Default is yes.

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

       aggressive-nsec: <yes or no>
              Aggressive  NSEC  uses the DNSSEC NSEC chain to synthesize 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 ad-
              dresses on your private network, and are not allowed to  be  re-
              turned  for  public  internet names.  Any occurrence of such ad-
              dresses 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 en-
              abled 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 ad-
              dresses.  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 ac-
              tion is to clear the rrset and message caches, hopefully  flush-
              ing  away  any poison.  A value of 10 million is suggested.  De-
              fault 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 re-
              quests.   It  does  use a little more CPU.  Also if the cache is
              set to 0, it is no use. Default is no.

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

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

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

       disable-dnssec-lame-check: <yes or no>
              If  true,  disables  the  DNSSEC lameness check in the iterator.
              This check sees if RRSIGs are present in the answer, when dnssec
              is  expected,  and retries another authority if RRSIGs are unex-
              pectedly missing.  The  validator  will  insist  in  RRSIGs  for
              DNSSEC signed domains regardless of this setting, if a trust an-
              chor 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
              respip, validator, or iterator (and possibly more,  see  below).
              Setting  this to just "iterator" will result in a non-validating
              server.  Setting this  to  "validator  iterator"  will  turn  on
              DNSSEC  validation.  The ordering of the modules is significant,
              the order decides the order of processing.  You  must  also  set
              trust-anchors for validation to be useful.  Adding respip to the
              front will cause RPZ processing to be done on all queries.   The
              default is "validator iterator".

              When the server is built with EDNS client subnet support the de-
              fault is "subnetcache validator iterator".   Most  modules  that
              need to be listed here have to be listed at the beginning of the
              line.  The subnetcachedb module has to be listed just before the
              iterator.   The python module can be listed in different places,
              it then processes the output of the module it  is  just  before.
              The dynlib module can be listed pretty much anywhere, it is only
              a very thin wrapper that allows dynamic libraries to run in  its
              place.

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

       auto-trust-anchor-file: <filename>
              File with trust anchor for  one  zone,  which  is  tracked  with
              RFC5011  probes.   The  probes  are run several times per month,
              thus the machine must be online frequently.   The  initial  file
              can be one with contents as described in trust-anchor-file.  The
              file is written to when the anchor is updated,  so  the  unbound
              user  must have write permission.  Write permission to the file,
              but also to the directory it is in (to create a temporary  file,
              which is necessary to deal with filesystem full events), it must
              also be inside the chroot (if that is used).

       trust-anchor: <"Resource Record">
              A DS or DNSKEY RR for a key to use for validation. Multiple  en-
              tries can be given to specify multiple trusted keys, in addition
              to the trust-anchor-files.  The resource record  is  entered  in
              the same format as 'dig' or 'drill' prints them, the same format
              as in the zone file. Has to be on a single line, with ""  around
              it. A TTL can be specified for ease of cut and paste, but is ig-
              nored.  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-an-
              chor-file but has a different  file  format.  Format  is  BIND-9
              style  format, the trusted-keys { name flag proto algo "key"; };
              clauses are read.  It is possible to  use  wildcards  with  this
              statement, the wildcard is expanded on start and on reload.

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

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

       domain-insecure: <domain name>
              Sets domain name to be insecure, DNSSEC chain of  trust  is  ig-
              nored  towards the domain name.  So a trust anchor above the do-
              main name can not make the domain secure with a DS record,  such
              a  DS  record  is  then ignored.  Can be given multiple times to
              specify multiple domains that are treated as  if  unsigned.   If
              you  set trust anchors for the domain they override this setting
              (and the domain is secured).

              This can be useful if you want to make sure a trust  anchor  for
              external  lookups does not affect an (unsigned) internal domain.
              A DS record externally can create validation failures  for  that
              internal domain.

       val-override-date: <rrsig-style date spec>
              Default  is "" or "0", which disables this debugging feature. If
              enabled by giving a RRSIG style date, that date is used for 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-max-restart: <number>
              The  maximum number the validator should restart validation with
              another authority in case of failed validation. Default is 5.

       val-bogus-ttl: <number>
              The time to live for bogus data. This is data  that  has  failed
              validation;  due  to invalid signatures or other checks. The TTL
              from that data cannot be trusted, and this  value  is  used  in-
              stead.  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 af-
              fected.  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.  Re-
              gardless 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 serve-expired-reply-ttl in  the  response  without
              waiting for the actual resolution to finish.  The actual resolu-
              tion answer ends up in the cache later on.  Default is "no".

       serve-expired-ttl: <seconds>
              Limit serving of expired responses to configured  seconds  after
              expiration. 0 disables the limit.  This option only applies when
              serve-expired is enabled.  A suggested value per RFC 8767 is be-
              tween 86400 (1 day) and 259200 (3 days).  The default is 0.

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

       serve-expired-reply-ttl: <seconds>
              TTL value to use when replying with expired data.  If  serve-ex-
              pired-client-timeout  is also used then it is RECOMMENDED to use
              30 as the value (RFC 8767).  The default is 30.

       serve-expired-client-timeout: <msec>
              Time in milliseconds before replying to the client with  expired
              data.   This  essentially  enables  the  serve-stale behavior as
              specified in RFC 8767 that first tries to resolve before immedi-
              ately responding with expired data.  A recommended value per RFC
              8767 is 1800.  Setting this to 0  will  disable  this  behavior.
              Default is 0.

       serve-original-ttl: <yes or no>
              If  enabled,  unbound will always return the original TTL as re-
              ceived from the upstream name server rather than the  decrement-
              ing  TTL  as stored in the cache.  This feature may be useful if
              unbound serves as a front-end to  a  hidden  authoritative  name
              server.  Enabling  this feature does not impact cache expiry, it
              only changes the TTL unbound embeds  in  responses  to  queries.
              Note  that enabling this feature implicitly disables enforcement
              of the configured minimum and maximum  TTL,  as  it  is  assumed
              users  who enable this feature do not want unbound to change the
              TTL obtained from an upstream server.  Thus, the values set  us-
              ing  cache-min-ttl  and  cache-max-ttl  are ignored.  Default is
              "no".

       val-nsec3-keysize-iterations: <"list of values">
              List of keysize and iteration count values, separated by spaces,
              surrounded  by  quotes. Default is "1024 150 2048 150 4096 150".
              This determines the maximum allowed NSEC3 iteration count before
              a  message  is  simply marked insecure instead of performing the
              many hashing iterations. The list must be in ascending order and
              have  at least one entry. If you set it to "1024 65535" there is
              no restriction to NSEC3 iteration values.  This  table  must  be
              kept short; a very long list could cause slower operation.

       zonemd-permissive-mode: <yes or no>
              If  enabled the ZONEMD verification failures are only logged and
              do not cause the zone to be blocked and  only  return  servfail.
              Useful  for  testing  out  if  it works, or if the operator only
              wants to be notified of a problem  without  disrupting  service.
              Default is no.

       add-holddown: <seconds>
              Instruct  the auto-trust-anchor-file probe mechanism for RFC5011
              autotrust updates to add new trust anchors only after they  have
              been visible for this time.  Default is 30 days as per the RFC.

       del-holddown: <seconds>
              Instruct  the auto-trust-anchor-file probe mechanism for RFC5011
              autotrust updates to remove revoked  trust  anchors  after  they
              have been kept in the revoked list for this long.  Default is 30
              days as per the RFC.

       keep-missing: <seconds>
              Instruct the auto-trust-anchor-file probe mechanism for  RFC5011
              autotrust  updates  to  remove  missing trust anchors after they
              have been unseen for this long.  This cleans up the  state  file
              if  the target zone does not perform trust anchor revocation, so
              this makes the auto probe mechanism work with zones that perform
              regular  (non-5011)  rollovers.   The  default is 366 days.  The
              value 0 does not remove missing anchors, as per the RFC.

       permit-small-holddown: <yes or no>
              Debug option that allows the autotrust 5011 rollover  timers  to
              assume very small values.  Default is no.

       key-cache-size: <number>
              Number  of  bytes size of the key cache. Default is 4 megabytes.
              A plain number is in bytes, append 'k', 'm'  or  'g'  for  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,  inform_redirect,  always_transparent,
              always_refuse, always_nxdomain, always_null, noview, and are ex-
              plained 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 re-
                 solved  normally.  If the query is for a name given in local-
                 data 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  de-
                 fault.

            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  an-
                 swers  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   lo-
                 cal-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.

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

            always_transparent
                 Like transparent, but ignores local data  and  resolves  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.

            always_nodata
                 Like static, but ignores local data and  returns  nodata  for
                 the query.

            always_deny
                 Like deny, but ignores local data and drops the query.

            always_null
                 Always  returns  0.0.0.0  or  ::0 for every name in the zone.
                 Like redirect with zero data for A and AAAA.   Ignores  local
                 data in the zone.  Used for some block lists.

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

            nodefault
                 Used to turn off default contents for AS112 zones. The  other
                 types also turn off default contents for the zone. The 'node-
                 fault' option has no other effect than  turning  off  default
                 contents  for  the  given zone.  Use nodefault if you use ex-
                 actly that zone, if you want to use a subzone, use  transpar-
                 ent.

       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 6761)
                 Default content:
                 local-zone: "test." static
                 local-data: "test. 10800 IN NS localhost."
                 local-data: "test. 10800 IN
                     SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"

            invalid (RFC 6761)
                 Default content:
                 local-zone: "invalid." static
                 local-data: "invalid. 10800 IN NS localhost."
                 local-data: "invalid. 10800 IN
                     SOA localhost. nobody.invalid. 1 3600 1200 604800 10800"

            reverse RFC1918 local use zones
                 Reverse data for zones  10.in-addr.arpa,  16.172.in-addr.arpa
                 to   31.172.in-addr.arpa,   168.192.in-addr.arpa.    The  lo-
                 cal-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  lo-
            cal-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 be-
            low.

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

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

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

       response-ip: <IP-netblock> <action>
            This requires use of the "respip" module.

            If  the  IP  address in an AAAA or A RR in the answer section of a
            response matches the specified IP netblock, the  specified  action
            will apply.  <action> has generally the same semantics as that for
            access-control-tag-action, but there are some exceptions.

            Actions for response-ip are different from those for local-zone in
            that in case of the former there is no point of such conditions as
            "the query matches it but there is no  local  data".   Because  of
            this difference, the semantics of response-ip actions are modified
            or simplified as follows: The static, refuse,  transparent,  type-
            transparent,  and  nodefault  actions are invalid for response-ip.
            Using any of these will cause the configuration to be rejected  as
            faulty. The deny action is non-conditional, i.e. it always results
            in dropping the corresponding query.  The resolution result before
            applying the deny action is still cached and can be used for other
            queries.

       response-ip-data: <IP-netblock> <"resource record string">
            This requires use of the "respip" module.

            This specifies the action data for response-ip with  action  being
            to  redirect  as specified by "resource record string".  "Resource
            record string" is similar to  that  of  access-control-tag-action,
            but  it  must be of either AAAA, A or CNAME types.  If the IP-net-
            block is an IPv6/IPV4 prefix, the record must  be  AAAA/A  respec-
            tively,  unless it is a CNAME (which can be used for both versions
            of IP netblocks).  If it is CNAME there must not be more than  one
            response-ip-data  for the same IP-netblock.  Also, CNAME and other
            types of records must not coexist for the same  IP-netblock,  fol-
            lowing  the  normal  rules  for CNAME records.  The textual domain
            name for the CNAME does not have to be explicitly terminated  with
            a  dot  (".");  the  root name is assumed to be the origin for the
            name.

       response-ip-tag: <IP-netblock> <"list of tags">
            This requires use of the "respip" module.

            Assign tags to response IP-netblocks.  If the  IP  address  in  an
            AAAA or A RR in the answer section of a response matches the spec-
            ified IP-netblock, the specified tags are assigned to the  IP  ad-
            dress.   Then,  if an access-control-tag is defined for the client
            and it includes one of the tags for the response  IP,  the  corre-
            sponding  access-control-tag-action will apply.  Tag matching rule
            is the same as that for access-control-tag and  local-zones.   Un-
            like local-zone-tag, response-ip-tag can be defined for an IP-net-
            block even if no response-ip is defined  for  that  netblock.   If
            multiple  response-ip-tag  options  are specified for the same IP-
            netblock in different statements, all but the first  will  be  ig-
            nored.   However,  this will not be flagged as a configuration er-
            ror, but the result is probably not what was intended.

            Actions specified  in  an  access-control-tag-action  that  has  a
            matching  tag with response-ip-tag can be those that are "invalid"
            for response-ip listed above, since access-control-tag-actions can
            be  shared  with  local  zones.  For these actions, if they behave
            differently depending on whether local data exists or not in  case
            of  local  zones, the behavior for response-ip-data will generally
            result in NOERROR/NODATA instead of NXDOMAIN, since the  response-
            ip  data  are  inherently type specific, and non-existence of data
            does not indicate anything about the existence or non-existence of
            the  qname  itself.   For  example,  if the matching tag action is
            static but there is no data for the corresponding response-ip con-
            figuration, then the result will be NOERROR/NODATA.  The only case
            where NXDOMAIN is returned is when an always_nxdomain  action  ap-
            plies.

       ratelimit: <number or 0>
            Enable  ratelimiting  of queries sent to nameserver for performing
            recursion.  If 0, the default, it is disabled.  This option is ex-
            perimental  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  ex-
            ceeded.   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 al-
            lowed.  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  ex-
            ceeded.   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 mit-
            igating the traffic flow by the factor given.

       fast-server-permil: <number>
            Specify how many times out of 1000 to pick from the set of fastest
            servers.  0 turns the feature off.  A value of 900 would pick from
            the fastest servers 90 percent of the time, and would perform nor-
            mal  exploration  of  random  servers for the remaining time. When
            prefetch is enabled (or serve-expired), such  prefetches  are  not
            sped up, because there is no one waiting for it, and it presents a
            good moment to perform server exploration. The fast-server-num op-
            tion  can  be used to specify the size of the fastest servers set.
            The default for fast-server-permil is 0.

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

       edns-client-string: <IP netblock> <string>
            Include  an  EDNS0  option  containing  configured ascii string in
            queries with destination address matching the configured  IP  net-
            block.   This configuration option can be used multiple times. The
            most specific match will be used.

       edns-client-string-opcode: <opcode>
            EDNS0 option code for the edns-client-string  option,  from  0  to
            65535.   A  value from the `Reserved for Local/Experimental` range
            (65001-65534) should be used.  Default is 65001.

   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 un-
       bound-control(8) utility also reads the remote-control section for  op-
       tions.   To  setup  the  correct  self-signed  certificates use the un-
       bound-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  ef-
            fect.

       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 un-
            bound_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  it-
       self 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 au-
       thoritative 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 lo-
       cal-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.  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.

       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 en-
       try with name "." and a forward-addr target will forward all queries to
       that other server (unless it can answer from the cache).

       name: <domain name>
              Name of the forward zone.

       forward-host: <domain name>
              Name of server to forward to. Is itself resolved  before  it  is
              used.

       forward-addr: <IP address>
              IP address of server to forward to. Can be IP 4 or IP 6.  To use
              a nondefault port for DNS communication append '@' with the port
              number.   If  tls  is  enabled,  then you can append a '#' and a
              name, then it'll check the tls authentication certificates  with
              that name.  If you combine the '@' and '#', the '@' comes first.

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

       forward-first: <yes or no>
              If a forwarded query is met with a SERVFAIL error, and this  op-
              tion is enabled, unbound will fall back to normal recursive res-
              olution for this query as if no query forwarding had been speci-
              fied.  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 de-
       tect zone changes.

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

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

       primary: <IP address or host name>
              Where  to  download a copy of the zone from, with AXFR and IXFR.
              Multiple primaries can be specified.  They are all tried if  one
              fails.   To  use  a nondefault port for DNS communication append
              '@' with the port number.  You can append a '#' and a name, then
              AXFR  over  TLS  can be used and the tls authentication certifi-
              cates will be checked with that name.  If you  combine  the  '@'
              and  '#',  the  '@' comes first.  If you point it at another Un-
              bound instance, it would not work because that does not  support
              AXFR/IXFR  for  the  zone,  but if you used url: to download the
              zonefile as a text file from a webserver that  would  work.   If
              you  specify  the  hostname,  you cannot use the domain from the
              zonefile, because it may not  have  that  when  retrieving  that
              data,  instead use a plain IP address to avoid a circular depen-
              dency on retrieving that IP address.

       master: <IP address or host name>
              Alternate syntax for primary.

       url: <url to zonefile>
              Where to download a zonefile for the zone.  With http or  https.
              An   example   for   the  url  is  "http://www.example.com/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  primaries  are
              listed,  the  primaries are first probed with UDP SOA queries to
              see if the SOA serial number has changed, reducing the number of
              downloads.   If  none  of the urls work, the primaries are tried
              with IXFR and AXFR.  For  https,  the  tls-cert-bundle  and  the
              hostname  from  the url are used to authenticate the connection.
              If you specify a hostname in the URL, you cannot use the  domain
              from  the zonefile, because it may not have that when retrieving
              that data, instead use a plain IP address to  avoid  a  circular
              dependency on retrieving that IP address.  Avoid dependencies on
              name lookups by using a notation like "http://192.0.2.1/unbound-
              primaries/example.com.zone", with an explicit IP address.

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

       fallback-enabled: <yes or no>
              Default  no.  If enabled, unbound falls back to querying the in-
              ternet as a resolver for this zone when lookups fail.  For exam-
              ple 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 be-
              have,  for  the queries with names in this zone, like one of the
              authority servers for that zone.  Turn it off if  you  want  un-
              bound 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 be-
              fore serving the zone contents to clients and  store  validation
              results in the cache.

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

       zonemd-check: <yes or no>
              Enable  this option to check ZONEMD records in the zone. Default
              is disabled.  The ZONEMD record is  a  checksum  over  the  zone
              data.  This  includes  glue  in  the zone and data from the zone
              file, and excludes comments from the zone file.  When there is a
              DNSSEC chain of trust, DNSSEC signatures are checked too.

       zonemd-reject-absence: <yes or no>
              Enable  this  option to reject the absence of the ZONEMD record.
              Without it, when zonemd is not there it is not checked.   It  is
              useful  to enable for a nonDNSSEC signed zone where the operator
              wants to require the verification of a ZONEMD, hence  a  missing
              ZONEMD  is  a failure.  The action upon failure is controlled by
              the zonemd-permissive-mode option, for log only  or  also  block
              the zone.  The default is no.

              Without  the  option  absence of a ZONEMD is only a failure when
              the zone is DNSSEC signed, and we have a trust anchor,  and  the
              DNSSEC  verification  of  the absence of the ZONEMD fails.  With
              the option enabled, the absence of a ZONEMD is always a failure,
              also for nonDNSSEC signed zones.

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

   View Options
       There may be multiple view: clauses. Each with a name: and zero or more
       local-zone  and local-data elements. Views can also contain view-first,
       response-ip, response-ip-data and local-data-ptr elements.  View can be
       mapped  to  requests  by  specifying  the  view  name in an access-con-
       trol-view element. Options from matching views will override global op-
       tions.  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  ac-
              cess-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 lo-
              cal-zones will be added to this view.  Defaults can be  disabled
              using  the nodefault type. When view-first is yes or when a view
              does not have a local-zone, the global local-zone will  be  used
              including it's default zones.

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

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

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

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

       If the chroot: option is enabled, you should make sure Python's library
       directory structure is bind mounted in the new  root  environment,  see
       mount(8).  Also the python-script: path should be specified as an 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. Repeat this option for every python
              module instance added to the module-config: option.

   Dynamic Library Module Options
       The dynlib: clause gives the settings for the dynlib module.  This mod-
       ule  is  only  a  very  small wrapper that allows dynamic modules to be
       loaded on runtime instead of being compiled into  the  application.  To
       enable the dynlib module it has to be compiled into the daemon, and the
       word "dynlib" has to be put in the module-config: option. Multiple  in-
       stances  of dynamic libraries are supported by adding the word "dynlib"
       more than once.

       The dynlib-file: path should be specified as an absolute path  relative
       to  the  new  path  set by chroot: option, or as a relative path to the
       working directory.

       dynlib-file: <dynlib file>
              The dynamic library file to load. Repeat this option  for  every
              dynlib module instance added to the module-config: option.

   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  en-
       abled.  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 al-
              low  one  to prime the new cert/key without distributing the new
              cert yet, this can be useful when using a network of servers us-
              ing  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 en-
       abled.  These settings go in the server: section.

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

       Additionally, when a client includes the option in its queries, Unbound
       will  forward  the  option when sending the query to addresses that are
       explicitly allowed in the configuration using  send-client-subnet.  The
       option  will  always be forwarded, regardless the allowed addresses, if
       client-subnet-always-forward is set to yes. In this case the lookup  in
       the regular cache is skipped.

       The  maximum size of the ECS cache is controlled by 'msg-cache-size' in
       the configuration file. On top of that, for each query only 100 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 in-
              dicate   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, un-
              less domain in query is specified in client-subnet-zone.

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

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

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

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

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

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

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

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

   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 en-
       abled.  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 an-
       swer  was found, unbound will call an external hook passing the follow-
       ing 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-allow: <domain>
              Allow the ipsecmod functionality for the domain so that the mod-
              ule  logic  will  be executed.  Can be given multiple times, for
              different domains.  If the option is not specified, all  domains
              are treated as being allowed (default).

       ipsecmod-whitelist: <yes or no>
              Alternate syntax for ipsecmod-allow.

   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  --en-
       able-cachedb.   If this module is enabled and configured, the specified
       backend database works as a second level  cache:  When  Unbound  cannot
       find  an answer to a query in its built-in in-memory cache, it consults
       the specified backend.  If it finds a valid answer in the backend,  Un-
       bound  uses it to respond to the query without performing iterative DNS
       resolution.  If Unbound cannot even find an answer in the  backend,  it
       resolves the query as usual, and stores the answer in the backend.

       This  module  interacts with the serve-expired-* options and will reply
       with expired data if unbound is configured for that.  Currently the use
       of  serve-expired-client-timeout:  and  serve-expired-reply-ttl: is not
       consistent for data originating from the external cache as  these  will
       result  in  a reply with 0 TTL without trying to update the data first,
       ignoring the configured values.

       If Unbound was built with --with-libhiredis on a system  that  has  in-
       stalled the hiredis C client library of Redis, then the "redis" backend
       can be used.  This backend communicates with the specified Redis server
       over a TCP connection to store and retrieve cache data.  It can be used
       as a persistent and/or shared cache backend.  It should be  noted  that
       Unbound  never  removes  data  stored in the Redis server, even if some
       data have expired in terms of DNS TTL or the Redis  server  has  cached
       too  much  data;  if  necessary  the Redis server must be configured to
       limit the cache size, preferably with some kind of  least-recently-used
       eviction  policy.  Additionally, the redis-expire-records option can be
       used in order to set the relative DNS TTL of the message as timeout  to
       the Redis records; keep in mind that some additional memory is used per
       key and that the expire information is stored as  absolute  Unix  time-
       stamps in Redis (computer time must be stable).  This backend uses syn-
       chronous communication with the Redis server based  on  the  assumption
       that  the  communication  is  stable and sufficiently fast.  The thread
       waiting for a response from the Redis server cannot  handle  other  DNS
       queries.   Although  the  backend  has  the ability to reconnect to the
       server when the connection is closed unexpectedly and there is  a  con-
       figurable  timeout in case the server is overly slow or hangs up, these
       cases are assumed to be very rare.  If connection close or timeout hap-
       pens too often, Unbound will be effectively unusable with this backend.
       It's the administrator's responsibility to make the assumption hold.

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

       backend: <backend name>
              Specify the backend database name.  The default database is  the
              in-memory  backend  named  "testframe",  which, as the name 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 de-
              faults 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  Re-
              dis  sever.   If this timeout expires Unbound closes the connec-
              tion, treats it as if the Redis server does  not  have  the  re-
              quested  data,  and  will  try  to re-establish a new connection
              later.  This option defaults to 100 milliseconds.

       redis-expire-records: <yes or no>
              If Redis record expiration is enabled.   If  yes,  unbound  sets
              timeout for Redis records so that Redis can evict keys that have
              expired automatically.  If unbound is configured with  serve-ex-
              pired  and serve-expired-ttl is 0, this option is internally re-
              verted to "no".  Redis SETEX support is required for this option
              (Redis >= 2.0.0).  This option defaults to no.

   DNSTAP Logging Options
       DNSTAP  support,  when  compiled in, is enabled in the dnstap: section.
       This starts an extra thread (when compiled with threading) that  writes
       the log information to the destination.  If unbound is compiled without
       threading it does not spawn a thread, but connects per-process  to  the
       destination.

       dnstap-enable: <yes or no>
              If  dnstap  is enabled.  Default no.  If yes, it connects to the
              dnstap server and if any of the  dnstap-log-..-messages  options
              is enabled it sends logs for those messages to the server.

       dnstap-bidirectional: <yes or no>
              Use  frame streams in bidirectional mode to transfer DNSTAP mes-
              sages. Default is yes.

       dnstap-socket-path: <file name>
              Sets the unix socket file name for connecting to the server that
              is listening on that socket.  Default is "".

       dnstap-ip: <IPaddress[@port]>
              If  "", the unix socket is used, if set with an IP address (IPv4
              or IPv6) that address is used to connect to the server.

       dnstap-tls: <yes or no>
              Set this to use TLS  to  connect  to  the  server  specified  in
              dnstap-ip.   The  default  is yes.  If set to no, TCP is used to
              connect to the server.

       dnstap-tls-server-name: <name of TLS authentication>
              The TLS server name to authenticate the server with.  Used  when
              dnstap-tls is enabled.  If "" it is ignored, default "".

       dnstap-tls-cert-bundle: <file name of cert bundle>
              The pem file with certs to verify the TLS server certificate. If
              "" the server default cert bundle is used, or the  windows  cert
              bundle on windows.  Default is "".

       dnstap-tls-client-key-file: <file name>
              The  client key file for TLS client authentication. If "" client
              authentication is not used.  Default is "".

       dnstap-tls-client-cert-file: <file name>
              The client cert file for TLS client authentication.  Default  is
              "".

       dnstap-send-identity: <yes or no>
              If enabled, the server identity is included in the log messages.
              Default is no.

       dnstap-send-version: <yes or no>
              If enabled, the server version if included in the log  messages.
              Default is no.

       dnstap-identity: <string>
              The  identity to send with messages, if "" the hostname is used.
              Default is "".

       dnstap-version: <string>
              The version to send with messages, if "" the package version  is
              used.  Default is "".

       dnstap-log-resolver-query-messages: <yes or no>
              Enable  to  log  resolver query messages.  Default is no.  These
              are messages from unbound to upstream servers.

       dnstap-log-resolver-response-messages: <yes or no>
              Enable to log resolver response messages.  Default is no.  These
              are replies from upstream servers to unbound.

       dnstap-log-client-query-messages: <yes or no>
              Enable  to log client query messages.  Default is no.  These are
              client queries to unbound.

       dnstap-log-client-response-messages: <yes or no>
              Enable to log client response messages.  Default is  no.   These
              are responses from unbound to clients.

       dnstap-log-forwarder-query-messages: <yes or no>
              Enable to log forwarder query messages.  Default is no.

       dnstap-log-forwarder-response-messages: <yes or no>
              Enable to log forwarder response messages.  Default is no.

   Response Policy Zone Options
       Response  Policy Zones are configured with rpz:, and each one must have
       a name:. There can be multiple ones, by listing multiple  rpz  clauses,
       each with a different name. RPZ clauses are applied in order of config-
       uration. The respip module needs to  be  added  to  the  module-config,
       e.g.: module-config: "respip validator iterator".

       Only the QNAME and Response IP Address triggers are supported. The sup-
       ported RPZ actions are: NXDOMAIN,  NODATA,  PASSTHRU,  DROP  and  Local
       Data. RPZ QNAME triggers are applied after local-zones and before auth-
       zones.

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

       primary: <IP address or host name>
              Where to download a copy of the zone from, with AXFR  and  IXFR.
              Multiple  primaries can be specified.  They are all tried if one
              fails.  To use a nondefault port for  DNS  communication  append
              '@' with the port number.  You can append a '#' and a name, then
              AXFR over TLS can be used and the  tls  authentication  certifi-
              cates  will  be  checked with that name.  If you combine the '@'
              and '#', the '@' comes first.  If you point it  at  another  Un-
              bound  instance, it would not work because that does not support
              AXFR/IXFR for the zone, but if you used  url:  to  download  the
              zonefile  as  a  text file from a webserver that would work.  If
              you specify the hostname, you cannot use  the  domain  from  the
              zonefile,  because  it  may  not  have that when retrieving that
              data, instead use a plain IP address to avoid a circular  depen-
              dency on retrieving that IP address.

       master: <IP address or host name>
              Alternate syntax for primary.

       url: <url to zonefile>
              Where  to download a zonefile for the zone.  With http or https.
              An  example  for  the   url   is   "http://www.example.com/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 primaries are
              listed, the primaries are first probed with UDP SOA  queries  to
              see if the SOA serial number has changed, reducing the number of
              downloads.  If none of the urls work, the  primaries  are  tried
              with  IXFR  and  AXFR.   For  https, the tls-cert-bundle and the
              hostname from the url are used to authenticate the connection.

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

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

       rpz-action-override: <action>
              Always use this RPZ action for matching triggers from this zone.
              Possible action are: nxdomain, nodata, passthru, drop,  disabled
              and cname.

       rpz-cname-override: <domain>
              The CNAME target domain to use if the cname action is configured
              for rpz-action-override.

       rpz-log: <yes or no>
              Log all applied RPZ actions for this RPZ zone. Default is no.

       rpz-log-name: <name>
              Specify a string to be part of the log line, for easy  referenc-
              ing.

       tags: <list of tags>
              Limit the policies from this RPZ clause to clients with a match-
              ing tag. Tags need to be defined in define-tag and  can  be  as-
              signed  to  client  addresses  using access-control-tag. Enclose
              list of tags in quotes ("") and put spaces between tags.  If  no
              tags are specified the policies from this clause will be applied
              for all clients.

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                       Aug 12, 2021                  unbound.conf(5)