Provided by: unbound_1.13.1-1_amd64 bug

NAME

       unbound.conf - Unbound configuration file.

SYNOPSIS

       unbound.conf

DESCRIPTION

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

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

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

EXAMPLE

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

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

       Most settings are the defaults. Stop the server with:

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

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

       # unbound.conf(5) config file for unbound(8).
       server:
            directory: "/etc/unbound"
            username: unbound
            # make sure unbound can access entropy from inside the chroot.
            # e.g. on linux the use these commands (on BSD, devfs(8) is used):
            #      mount --bind -n /dev/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 anywhere, it  accepts  a
       single  file name as argument.  Processing continues as if the text from the included file
       was copied into the config file at that point.  If also  using  chroot,  using  full  path
       names  for the included files works, relative pathnames for the included names work if the
       directory where the daemon is started equals its chroot/working directory or is  specified
       before  the  include  statement  with  directory:  dir.   Wildcards can be used to include
       multiple files, see glob(7).

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

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

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

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

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

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

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

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

       interface-automatic: <yes or no>
              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 select 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  interfaces. If none are given the default (all) is used. You can
              specify the same  interfaces  in  interface:  and  outgoing-interface:  lines,  the
              interfaces  are then used for both purposes. Outgoing queries are sent via a random
              outgoing interface to counter spoofing.

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

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

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

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

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

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

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

       edns-buffer-size: <number>
              Number of bytes size to advertise as the EDNS reassembly buffer size.  This is  the
              value  put  into  datagrams  over  UDP  towards  peers.   The actual buffer size is
              determined by msg-buffer-size (both for TCP and UDP).  Do not set higher than  that
              value.   Default  is 1232 which is the DNS Flag Day 2020 recommendation. Setting to
              512 bypasses even the most stringent path MTU problems, but  is  seen  as  extreme,
              since  the  amount  of  TCP fallback generated is excessive (probably also for this
              resolver, consider tuning the outgoing tcp number).

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

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

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

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

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

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

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

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

       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 reply.  Increase this if
              you  are  behind  a  slow  satellite  link,  to  eg.  1128.   That would then avoid
              re-querying every initial query because it times out.  Default is 376 msec.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       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-control.   Enclose  the
              list between quotes ("") and put spaces between tags.

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

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

       prefer-ip4: <yes or no>
              If  enabled, prefer IPv4 transport for sending DNS queries to internet nameservers.
              Default is no.  Useful if the IPv6 netblock the server has, the entire /64 of  that
              is  not  owned  by one operator 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 internet  nameservers.
              Default is no.

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

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

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

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

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

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

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

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

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

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

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

       tls-service-key: <file>
              If enabled, the server provides 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 contain the private key for the TLS session,  the  public
              certificate  is  in  the  tls-service-pem  file  and  it  must also be specified if
              tls-service-key is  specified.   The  default  is  "",  turned  off.   Enabling  or
              disabling this service requires a restart (a reload is not enough), because the key
              is read while root permissions are held and before  chroot  (if  any).   The  ports
              enabled  implicitly  or  explicitly  via  tls-port:  and https-port: do not provide
              normal DNS TCP service. Unbound needs to be compiled with libnghttp2  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.  Default is "", turned
              off.

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

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

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

       tls-cert-bundle: <file>
              If null or "", no file is used.  Set it to the certificate bundle file, for example
              "/etc/pki/tls/certs/ca-bundle.crt".  These certificates are used for authenticating
              connections  made  to outside peers.  For example auth-zone urls, and also DNS over
              TLS connections.  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 certificates.  Default is no.  On windows this
              option uses the certificates from the cert store.  Use the  tls-cert-bundle  option
              on other systems.

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

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

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

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

       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 upstreams.  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, default 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. Default 100.

       http-query-buffer-size: <size in bytes>
              Maximum  number  of bytes used for all HTTP/2 query buffers combined. 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. Default 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 appended for a  classless
              network  block.  The  action  can be deny, refuse, allow, allow_setrd, allow_snoop,
              deny_non_local or refuse_non_local.  The most specific netblock match is  used,  if
              none match deny is used.  The order of the access-control statements therefore does
              not matter.

              The action deny stops queries from hosts from that netblock.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       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 numbers.   The  default
              is  "3  2 1 0 0". Setting all zeroes, "0 0 0 0 0" gives behaviour closer to that of
              BIND 9, while setting "-1 -1 -1 -1 -1" gives behaviour rumoured  to  be  closer  to
              that of BIND 8.

       harden-short-bufsize: <yes or no>
              Very  small EDNS buffer sizes from queries are ignored. Default is on, as described
              in the standard.

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

       harden-glue: <yes or no>
              Will trust glue only if it is within the servers authority. Default is 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 attack 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 Underneath"),  returns
              nxdomain  to  queries  for  a  name  below another name that is already known to be
              nxdomain.  DNSSEC mandates noerror for empty nonterminals, hence this is  possible.
              Very old software might return nxdomain for empty nonterminals (that usually happen
              for reverse IP address lookups), and thus may be incompatible with this.  To try to
              avoid this only DNSSEC-secure nxdomains are used, because the old software does not
              have DNSSEC.  Default is 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 validation on nameserver NS sets and the nameserver addresses
              that are encountered on the referral path to the answer.  Default  no,  because  it
              burdens  the  authority  servers,  and  it  is  not RFC standard, and could lead to
              performance  problems  because  of  the  extra  query  load  that   is   generated.
              Experimental  option.   If  you  enable  it  consider adding more numbers after the
              target-fetch-policy to increase the max depth that is checked to.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       module-config: <"module names">
              Module configuration, a list of module names  separated  by  spaces,  surround  the
              string  with  quotes (""). The modules can be validator, iterator.  Setting this to
              "iterator" will result in a non-validating  server.   Setting  this  to  "validator
              iterator"  will  turn  on  DNSSEC  validation.   The  ordering  of  the  modules is
              important.  You must also set trust-anchors  for  validation  to  be  useful.   The
              default  is "validator iterator".  When the server is built with EDNS client subnet
              support the default is "subnetcache validator iterator".  Most modules that need to
              be  listed here have to be listed at the beginning of the line.  The cachedb module
              has to be listed just before the iterator.  The python  module  can  be  listed  in
              different places, it then processes the output of the module it is just before. 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 entries can appear in the
              file. The format of the file is the standard DNS Zone file format.  Default is  "",
              or no trust anchor file.

       auto-trust-anchor-file: <filename>
              File  with  trust  anchor  for one zone, which is tracked with RFC5011 probes.  The
              probes are 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 entries can be given to
              specify multiple trusted keys, in addition to the trust-anchor-files.  The resource
              record  is  entered  in  the  same format as 'dig' or 'drill' prints them, the same
              format as in the zone file. Has to be on a single line, with "" around  it.  A  TTL
              can  be  specified  for  ease  of  cut  and  paste, but is ignored.  A class can be
              specified, but class IN is default.

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

       trust-anchor-signaling: <yes or no>
              Send RFC8145 key tag query after trust anchor priming. Default is 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  ignored  towards  the
              domain  name.   So  a  trust  anchor  above the domain name can not make the domain
              secure with a DS record, such a DS record is then ignored.  Can be  given  multiple
              times  to  specify  multiple  domains  that are treated as if unsigned.  If you set
              trust anchors for the  domain  they  override  this  setting  (and  the  domain  is
              secured).

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

       val-override-date: <rrsig-style date spec>
              Default is "" or "0", which disables this debugging feature. If enabled by giving a
              RRSIG style date, that date is used for verifying RRSIG  inception  and  expiration
              dates,  instead  of  the  current  date.  Do  not set this unless you are debugging
              signature inception and expiration. The  value  -1  ignores  the  date  altogether,
              useful for some special applications.

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

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

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

       val-clean-additional: <yes or no>
              Instruct the validator to  remove  data  from  the  additional  section  of  secure
              messages  that  are  not  signed  properly.  Messages  that  are  insecure,  bogus,
              indeterminate or unchecked are not affected. Default is yes. Use  this  setting  to
              protect  the  users that rely on this validator for authentication from potentially
              bad data in the additional section.

       val-log-level: <number>
              Have the validator print  validation  failures  to  the  log.   Regardless  of  the
              verbosity  setting.   Default  is  0, off.  At 1, for every user query that fails a
              line is printed  to  the  logs.   This  way  you  can  monitor  what  happens  with
              validation.  Use a diagnosis tool, such as dig or drill, to find out why validation
              is failing for these queries.  At 2, not only the query that failed is printed  but
              also  the  reason why unbound thought it was wrong and which server sent the faulty
              data.

       val-permissive-mode: <yes or no>
              Instruct the validator to mark bogus messages as indeterminate. The security checks
              are  performed,  but  if  the  result  is bogus (failed security), the reply is not
              withheld from the client with SERVFAIL as usual.  The  client  receives  the  bogus
              data.  For  messages that are found to be secure the AD bit is set in replies. Also
              logging is performed as for full validation.  The default value is "no".

       ignore-cd-flag: <yes or no>
              Instruct unbound to ignore the CD flag from clients  and  refuse  to  return  bogus
              answers  to  them.  Thus, the CD (Checking Disabled) flag does not disable checking
              any more.  This is useful if legacy (w2008) servers that set the CD flag but cannot
              validate  DNSSEC  themselves  are  the clients, and then unbound provides them with
              DNSSEC protection.  The default value is "no".

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

       serve-expired-ttl: <seconds>
              Limit  serving  of  expired  responses  to  configured  seconds after expiration. 0
              disables the limit.  This option only applies when  serve-expired  is  enabled.   A
              suggested  value  per  RFC  8767 is between 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-expired-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 immediately 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  received  from  the
              upstream name server rather than the decrementing 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 using 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  500 4096 2500". This determines the maximum
              allowed NSEC3 iteration count before a message is simply marked insecure instead of
              performing  the  many  hashing  iterations. The list must be in ascending order and
              have at least one entry. If you set it to "1024 65535" there is no  restriction  to
              NSEC3  iteration  values.   This  table  must be kept short; a very long list could
              cause slower operation.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

            test (RFC 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 local-zone: is set static and as
                 local-data: SOA and NS records are provided.

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

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

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

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

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

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

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

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

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

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

       ratelimit: <number or 0>
            Enable  ratelimiting  of  queries sent to nameserver for performing recursion.  If 0,
            the default, it is  disabled.   This  option  is  experimental  at  this  time.   The
            ratelimit  is  in  queries per second that are allowed.  More queries are turned away
            with an error (servfail).  This stops recursive floods, eg. random query  names,  but
            not spoofed reflection floods.  Cached responses are not ratelimited by this setting.
            The zone of the query is determined by examining the nameservers  for  it,  the  zone
            name is used to keep track of the rate.  For example, 1000 may be a suitable value to
            stop the server from being overloaded with  random  names,  and  keeps  unbound  from
            sending traffic to the nameservers for those zones.

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

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

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

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

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

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

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

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

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

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

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

       edns-client-string: <IP netblock> <string>
            Include   an  EDNS0  option  containing  configured  ascii  string  in  queries  with
            destination address matching the configured IP netblock.  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 control facility.  If
       this is enabled, the unbound-control(8) utility can  be  used  to  send  commands  to  the
       running  unbound  server.   The  server uses these clauses to setup TLSv1 security for the
       connection.  The unbound-control(8) utility also  reads  the  remote-control  section  for
       options.   To  setup the correct self-signed certificates use the unbound-control-setup(8)
       utility.

       control-enable: <yes or no>
            The option is used to enable remote control, default is "no".   If  turned  off,  the
            server does not listen for control commands.

       control-interface: <ip address or path>
            Give  IPv4  or IPv6 addresses or local socket path to listen on for control commands.
            By default localhost (127.0.0.1 and ::1) is listened to.   Use  0.0.0.0  and  ::0  to
            listen  to all interfaces.  If you change this and permissions have been dropped, you
            must restart the server for the change to take effect.

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

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

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

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

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

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

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

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

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

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

       Consider adding server: statements for domain-insecure: and for local-zone: name nodefault
       for the zone if it is a locally served  zone.   The  insecure  clause  stops  DNSSEC  from
       invalidating  the  zone.   The  local  zone  nodefault  (or  transparent) clause makes the
       (reverse-) zone bypass unbound's filtering of RFC1918 zones.

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

       stub-host: <domain name>
              Name of stub zone nameserver. Is itself resolved before it is used.

       stub-addr: <IP address>
              IP address of stub zone nameserver. Can be IP 4 or IP 6.  To use a nondefault  port
              for DNS communication append '@' with the port number.  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 entry with
       name "." and a forward-addr target will forward all queries to that other  server  (unless
       it can answer from the cache).

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

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

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

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

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

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

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

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

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

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

       If the update fetch fails, the timers in the SOA record are used  to  time  another  fetch
       attempt.   Until  the SOA expiry timer is reached.  Then the zone is expired.  When a zone
       is expired, queries are SERVFAIL, and any new serial number is accepted from  the  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.  With the "ip#name" notation a
              AXFR over TLS can be used.  If you point it at another Unbound 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 dependency 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/example.org.zone".  Multiple url statements  can  be
              given,  they  are  tried  in turn.  If only urls are given the SOA refresh timer is
              used to wait for making new downloads.  If also 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 notifies.  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 allowed notify by default.

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

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

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

       zonefile: <filename>
              The filename where the zone is stored.  If not given then no zonefile is used.   If
              the  file  does not exist or is empty, unbound will attempt to fetch zone data (eg.
              from the 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-control-view  element.  Options  from  matching views will override global options.
       Global options will be used if no matching view is found, or when the matching  view  does
       not have the option specified.

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

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

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

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

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

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

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

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

   Dynamic Library Module Options
       The  dynlib:  clause gives the settings for the dynlib module.  This module 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
       instances 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 validator iterator"
       directive and be compiled into the daemon to be enabled.  These settings go in the server:
       section.

       dns64-prefix: <IPv6 prefix>
              This  sets the DNS64 prefix to use to synthesize AAAA records with.  It must be /96
              or shorter.  The default prefix is 64:ff9b::/96.

       dns64-synthall: <yes or no>
              Debug option, default no.  If enabled, synthesize  all  AAAA  records  despite  the
              presence of actual AAAA records.

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

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

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

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

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

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

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

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

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

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

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

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

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

       If  the  destination  address  is  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 indicated no support, the response is stored in the regular cache.

       Additionally, when a client includes the option in its queries, Unbound will  forward  the
       option   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 different subnets are allowed to be stored
       for each address family. Exceeding that number, older entries will be purged from cache.

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

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

       client-subnet-always-forward: <yes or no>
              Specify  whether  the  ECS  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  enabled,  the
              address  check  is  skipped  when  the client query contains 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 enabled.  These settings go in the server:
       section.

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

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

            IPSECKEY TTL
                 TTL of the IPSECKEY RRset.

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

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

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

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

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

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

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

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

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

       ipsecmod-allow: <domain>
              Allow  the  ipsecmod  functionality for the domain so that the module logic will be
              executed.  Can be given multiple times, for different domains.  If  the  option  is
              not specified, all domains are treated as being 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  --enable-cachedb.   If  this  module  is
       enabled and configured, the specified backend database works as a second level cache: When
       Unbound cannot find an answer to a query in its built-in in-memory cache, it consults  the
       specified  backend.  If it finds a valid answer in the backend, Unbound uses it to respond
       to the query without performing iterative DNS resolution.  If Unbound cannot even find  an
       answer  in  the  backend,  it  resolves  the  query as usual, and stores the answer in the
       backend.

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

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

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

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

       The following cachedb otions are specific to the redis backend.

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

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

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

       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-expired  and  serve-expired-ttl  is  0,  this option is
              internally reverted 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  messages.  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 "/run/dnstap.sock".

       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 configuration. 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 supported 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.

       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/example.org.zone".  Multiple url statements can be
              given, they are tried in turn.  If only urls are given the  SOA  refresh  timer  is
              used to wait for making new downloads.  If also 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 notifies.  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 allowed 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, unbound 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 referencing.

       tags: <list of tags>
              Limit  the  policies from this RPZ clause to clients with a matching tag. Tags need
              to be defined  in  define-tag  and  can  be  assigned  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 service levels are
       lower, notable very large data and a high TCP load are no  longer  supported.  Very  large
       data  and  high TCP loads are exceptional for the DNS.  DNSSEC validation is enabled, just
       add trust anchors.  If you do not have to worry about programs using more  than  3  Mb  of
       memory,  the below example is not for you. Use the defaults to receive full service, which
       on BSD-32bit tops out at 30-40 Mb after heavy usage.

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

FILES

       /etc/unbound
              default unbound working directory.

       default
              chroot(2) location.

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

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

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

SEE ALSO

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

AUTHORS

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