- Copy stable/10@285827 to releng/10.2 in preparation for 10.2-RC1

[FreeBSD/releng/10.2.git] / contrib / unbound / doc / example.conf.in

#
# Example configuration file.
#
# See unbound.conf(5) man page, version 1.5.3.
#
# this is a comment.

#Use this to include other text into the file.
#include: "otherfile.conf"

# The server clause sets the main parameters. 
server:
        # whitespace is not necessary, but looks cleaner.

        # verbosity number, 0 is least verbose. 1 is default.
        verbosity: 1

        # print statistics to the log (for every thread) every N seconds.
        # Set to "" or 0 to disable. Default is disabled.
        # statistics-interval: 0

        # enable cumulative statistics, without clearing them after printing.
        # statistics-cumulative: no

        # enable extended statistics (query types, answer codes, status)
        # printed from unbound-control. default off, because of speed.
        # extended-statistics: no

        # number of threads to create. 1 disables threading.
        # num-threads: 1

        # specify the interfaces to answer queries from by ip-address.
        # The default is to listen to localhost (127.0.0.1 and ::1).
        # specify 0.0.0.0 and ::0 to bind to all available interfaces.
        # specify every interface[@port] on a new 'interface:' labelled line.
        # The listen interfaces are not changed on reload, only on restart.
        # interface: 192.0.2.153
        # interface: 192.0.2.154
        # interface: 192.0.2.154@5003
        # interface: 2001:DB8::5

        # enable this feature to copy the source address of queries to reply.
        # Socket options are not supported on all platforms. experimental. 
        # interface-automatic: no

        # port to answer queries from
        # port: 53

        # specify the interfaces to send outgoing queries to authoritative
        # server from by ip-address. If none, the default (all) interface
        # is used. Specify every interface on a 'outgoing-interface:' line.
        # outgoing-interface: 192.0.2.153
        # outgoing-interface: 2001:DB8::5
        # outgoing-interface: 2001:DB8::6

        # number of ports to allocate per thread, determines the size of the
        # port range that can be open simultaneously.  About double the
        # num-queries-per-thread, or, use as many as the OS will allow you.
        # outgoing-range: 4096

        # permit unbound to use this port number or port range for
        # making outgoing queries, using an outgoing interface.
        # outgoing-port-permit: 32768

        # deny unbound the use this of port number or port range for
        # making outgoing queries, using an outgoing interface.
        # Use this to make sure unbound does not grab a UDP port that some
        # other server on this computer needs. The default is to avoid
        # IANA-assigned port numbers.
        # If multiple outgoing-port-permit and outgoing-port-avoid options
        # are present, they are processed in order.
        # outgoing-port-avoid: "3200-3208"

        # number of outgoing simultaneous tcp buffers to hold per thread.
        # outgoing-num-tcp: 10

        # number of incoming simultaneous tcp buffers to hold per thread.
        # incoming-num-tcp: 10

        # buffer size for UDP port 53 incoming (SO_RCVBUF socket option).
        # 0 is system default.  Use 4m to catch query spikes for busy servers.
        # so-rcvbuf: 0

        # buffer size for UDP port 53 outgoing (SO_SNDBUF socket option).
        # 0 is system default.  Use 4m to handle spikes on very busy servers.
        # so-sndbuf: 0
        
        # use SO_REUSEPORT to distribute queries over threads.
        # so-reuseport: no

        # EDNS reassembly buffer to advertise to UDP peers (the actual buffer
        # is set with msg-buffer-size). 1480 can solve fragmentation (timeouts).
        # edns-buffer-size: 4096

        # Maximum UDP response size (not applied to TCP response).
        # Suggested values are 512 to 4096. Default is 4096. 65536 disables it.
        # max-udp-size: 4096

        # buffer size for handling DNS data. No messages larger than this
        # size can be sent or received, by UDP or TCP. In bytes.
        # msg-buffer-size: 65552

        # the amount of memory to use for the message cache.
        # plain value in bytes or you can append k, m or G. default is "4Mb". 
        # msg-cache-size: 4m

        # the number of slabs to use for the message cache.
        # the number of slabs must be a power of 2.
        # more slabs reduce lock contention, but fragment memory usage.
        # msg-cache-slabs: 4

        # the number of queries that a thread gets to service.
        # num-queries-per-thread: 1024

        # if very busy, 50% queries run to completion, 50% get timeout in msec
        # jostle-timeout: 200
        
        # msec to wait before close of port on timeout UDP. 0 disables.
        # delay-close: 0

        # the amount of memory to use for the RRset cache.
        # plain value in bytes or you can append k, m or G. default is "4Mb". 
        # rrset-cache-size: 4m

        # the number of slabs to use for the RRset cache.
        # the number of slabs must be a power of 2.
        # more slabs reduce lock contention, but fragment memory usage.
        # rrset-cache-slabs: 4

        # the time to live (TTL) value lower bound, in seconds. Default 0.
        # If more than an hour could easily give trouble due to stale data.
        # cache-min-ttl: 0

        # the time to live (TTL) value cap for RRsets and messages in the
        # cache. Items are not cached for longer. In seconds.
        # cache-max-ttl: 86400

        # the time to live (TTL) value for cached roundtrip times, lameness and
        # EDNS version information for hosts. In seconds.
        # infra-host-ttl: 900
        
        # minimum wait time for responses, increase if uplink is long. In msec.
        # infra-cache-min-rtt: 50

        # the number of slabs to use for the Infrastructure cache.
        # the number of slabs must be a power of 2.
        # more slabs reduce lock contention, but fragment memory usage.
        # infra-cache-slabs: 4

        # the maximum number of hosts that are cached (roundtrip, EDNS, lame).
        # infra-cache-numhosts: 10000

        # Enable IPv4, "yes" or "no".
        # do-ip4: yes

        # Enable IPv6, "yes" or "no".
        # do-ip6: yes

        # Enable UDP, "yes" or "no".
        # do-udp: yes

        # Enable TCP, "yes" or "no".
        # do-tcp: yes

        # upstream connections use TCP only (and no UDP), "yes" or "no"
        # useful for tunneling scenarios, default no.
        # tcp-upstream: no

        # Detach from the terminal, run in background, "yes" or "no".
        # do-daemonize: yes

        # control which clients are allowed to make (recursive) queries
        # to this server. Specify classless netblocks with /size and action.
        # By default everything is refused, except for localhost.
        # Choose deny (drop message), refuse (polite error reply),
        # allow (recursive ok), allow_snoop (recursive and nonrecursive ok)
        # deny_non_local (drop queries unless can be answered from local-data)
        # refuse_non_local (like deny_non_local but polite error reply).
        # access-control: 0.0.0.0/0 refuse
        # access-control: 127.0.0.0/8 allow
        # access-control: ::0/0 refuse
        # access-control: ::1 allow
        # access-control: ::ffff:127.0.0.1 allow

        # if given, a chroot(2) is done to the given directory.
        # i.e. you can chroot to the working directory, for example,
        # for extra security, but make sure all files are in that 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:
        #       o as an absolute path relative to the new root.
        #       o as a relative path to the working directory.
        #       o as an absolute path relative to the original root.
        # In the last case the path is adjusted to remove the unused portion.
        #
        # The pid file can be absolute and outside of the chroot, it is 
        # written just prior to performing the chroot and dropping permissions.
        #
        # Additionally, unbound may need to access /dev/random (for entropy).
        # How to do this is specific to your OS.
        #
        # If you give "" no chroot is performed. The path must not end in a /.
        # chroot: "@UNBOUND_CHROOT_DIR@"

        # if given, user privileges are dropped (after binding port),
        # and the given username is assumed. Default is user "unbound".
        # If you give "" no privileges are dropped.
        # username: "@UNBOUND_USERNAME@"

        # the working directory. The relative files in this config are 
        # relative to this directory. If you give "" the working directory
        # is not changed.
        # directory: "@UNBOUND_RUN_DIR@"

        # the log file, "" means log to stderr. 
        # Use of this option sets use-syslog to "no".
        # logfile: ""

        # Log to syslog(3) if yes. The log facility LOG_DAEMON is used to 
        # log to, with identity "unbound". If yes, it overrides the logfile.
        # use-syslog: yes 

        # print UTC timestamp in ascii to logfile, default is epoch in seconds.
        # log-time-ascii: no
        
        # print one line with time, IP, name, type, class for every query.
        # log-queries: no

        # the pid file. Can be an absolute path outside of chroot/work dir.
        # pidfile: "@UNBOUND_PIDFILE@"

        # file to read root hints from.
        # get one from ftp://FTP.INTERNIC.NET/domain/named.cache
        # root-hints: ""

        # enable to not answer id.server and hostname.bind queries.
        # hide-identity: no

        # enable to not answer version.server and version.bind queries.
        # hide-version: no

        # the identity to report. Leave "" or default to return hostname.
        # identity: ""

        # the version to report. Leave "" or default to return package version.
        # version: ""

        # the target fetch policy.
        # series of integers describing the policy per dependency depth. 
        # The number of values in the list determines the maximum dependency 
        # depth the recursor will pursue before giving up. Each integer means:
        #       -1 : fetch all targets opportunistically,
        #       0: fetch on demand,
        #       positive value: fetch that many targets opportunistically.
        # Enclose the list of numbers between quotes ("").
        # target-fetch-policy: "3 2 1 0 0"

        # Harden against very small EDNS buffer sizes. 
        # harden-short-bufsize: no

        # Harden against unseemly large queries.
        # harden-large-queries: no

        # Harden against out of zone rrsets, to avoid spoofing attempts. 
        # harden-glue: yes

        # Harden against receiving dnssec-stripped data. If you turn it
        # off, failing to validate dnskey data for a trustanchor will 
        # trigger insecure mode for that zone (like without a trustanchor).
        # Default on, which insists on dnssec data for trust-anchored zones.
        # harden-dnssec-stripped: yes

        # Harden against queries that fall under dnssec-signed nxdomain names.
        # harden-below-nxdomain: no

        # Harden the referral path by performing additional queries for
        # infrastructure data.  Validates the replies (if possible).
        # Default off, because the lookups burden the server.  Experimental 
        # implementation of draft-wijngaards-dnsext-resolver-side-mitigation.
        # harden-referral-path: no

        # Use 0x20-encoded random bits in the query to foil spoof attempts.
        # This feature is an experimental implementation of draft dns-0x20.
        # use-caps-for-id: no

        # Enforce privacy of these addresses. Strips them away from answers. 
        # It may cause DNSSEC validation to additionally mark it as bogus. 
        # Protects against 'DNS Rebinding' (uses browser as network proxy). 
        # Only 'private-domain' and 'local-data' names are allowed to have 
        # these private addresses. No default.
        # private-address: 10.0.0.0/8
        # private-address: 172.16.0.0/12
        # private-address: 192.168.0.0/16
        # private-address: 169.254.0.0/16
        # private-address: fd00::/8
        # private-address: fe80::/10

        # Allow the domain (and its subdomains) to contain private addresses.
        # local-data statements are allowed to contain private addresses too.
        # private-domain: "example.com"

        # If nonzero, unwanted replies are not only reported in statistics,
        # but also a running total is kept per thread. If it reaches the
        # threshold, a warning is printed and a defensive action is taken,
        # the cache is cleared to flush potential poison out of it.
        # A suggested value is 10000000, the default is 0 (turned off).
        # unwanted-reply-threshold: 0

        # Do not query the following addresses. No DNS queries are sent there.
        # List one address per entry. List classless netblocks with /size,
        # do-not-query-address: 127.0.0.1/8
        # do-not-query-address: ::1

        # if yes, the above default do-not-query-address entries are present.
        # if no, localhost can be queried (for testing and debugging).
        # do-not-query-localhost: yes

        # if yes, perform prefetching of almost expired message cache entries.
        # prefetch: no

        # if yes, perform key lookups adjacent to normal lookups.
        # prefetch-key: no

        # if yes, Unbound rotates RRSet order in response.
        # rrset-roundrobin: no

        # if yes, Unbound doesn't insert authority/additional sections
        # into response messages when those sections are not required.
        # minimal-responses: no

        # module configuration of the server. A string with identifiers
        # separated by spaces. Syntax: "[dns64] [validator] iterator"
        # module-config: "validator iterator"

        # File with trusted keys, kept uptodate using RFC5011 probes,
        # initial file like trust-anchor-file, then it stores metadata.
        # Use several entries, one per domain name, to track multiple zones.
        #
        # If you want to perform DNSSEC validation, run unbound-anchor before
        # you start unbound (i.e. in the system boot scripts).  And enable:
        # Please note usage of unbound-anchor root anchor is at your own risk
        # and under the terms of our LICENSE (see that file in the source).
        # auto-trust-anchor-file: "@UNBOUND_ROOTKEY_FILE@"

        # File with DLV trusted keys. Same format as trust-anchor-file.
        # There can be only one DLV configured, it is trusted from root down.
        # Download http://ftp.isc.org/www/dlv/dlv.isc.org.key
        # dlv-anchor-file: "dlv.isc.org.key"

        # File with trusted keys for validation. Specify more than one file
        # with several entries, one file per entry.
        # Zone file format, with DS and DNSKEY entries.
        # Note this gets out of date, use auto-trust-anchor-file please.
        # trust-anchor-file: ""
        
        # Trusted key for validation. DS or DNSKEY. specify the RR on a
        # single line, surrounded by "". TTL is ignored. class is IN default.
        # Note this gets out of date, use auto-trust-anchor-file please.
        # (These examples are from August 2007 and may not be valid anymore).
        # trust-anchor: "nlnetlabs.nl. DNSKEY 257 3 5 AQPzzTWMz8qSWIQlfRnPckx2BiVmkVN6LPupO3mbz7FhLSnm26n6iG9N Lby97Ji453aWZY3M5/xJBSOS2vWtco2t8C0+xeO1bc/d6ZTy32DHchpW 6rDH1vp86Ll+ha0tmwyy9QP7y2bVw5zSbFCrefk8qCUBgfHm9bHzMG1U BYtEIQ=="
        # trust-anchor: "jelte.nlnetlabs.nl. DS 42860 5 1 14D739EB566D2B1A5E216A0BA4D17FA9B038BE4A"

        # 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.
        # you need external update procedures to track changes in keys.
        # trusted-keys-file: ""

        # Ignore chain of trust. Domain is treated as insecure.
        # domain-insecure: "example.com"

        # Override the date for validation with a specific fixed date.
        # Do not set this unless you are debugging signature inception
        # and expiration. "" or "0" turns the feature off. -1 ignores date.
        # val-override-date: ""

        # The time to live for bogus data, rrsets and messages. This avoids
        # some of the revalidation, until the time interval expires. in secs.
        # val-bogus-ttl: 60

        # The signature inception and expiration dates are allowed to be off
        # by 10% of the signature lifetime (expir-incep) from our local clock.
        # This leeway is capped with a minimum and a maximum.  In seconds.
        # val-sig-skew-min: 3600
        # val-sig-skew-max: 86400

        # Should additional section of secure message also be kept clean of
        # unsecure data. Useful to shield the users of this validator from
        # potential bogus data in the additional section. All unsigned data 
        # in the additional section is removed from secure messages.
        # val-clean-additional: yes

        # Turn permissive mode on to permit bogus messages. Thus, messages
        # for which security checks failed will be returned to clients,
        # instead of SERVFAIL. It still performs the security checks, which
        # result in interesting log files and possibly the AD bit in
        # replies if the message is found secure. The default is off.
        # val-permissive-mode: no

        # Ignore the CD flag in incoming queries and refuse them bogus data.
        # Enable it if the only clients of unbound are legacy servers (w2008)
        # that set CD but cannot validate themselves.
        # ignore-cd-flag: no

        # Have the validator log failed validations for your diagnosis.
        # 0: off. 1: A line per failed user query. 2: With reason and bad IP.
        # val-log-level: 0

        # It is possible to configure NSEC3 maximum iteration counts per
        # keysize. Keep this table very short, as linear search is done.
        # A message with an NSEC3 with larger count is marked insecure.
        # List in ascending order the keysize and count values.
        # val-nsec3-keysize-iterations: "1024 150 2048 500 4096 2500"
        
        # instruct the auto-trust-anchor-file probing to add anchors after ttl.
        # add-holddown: 2592000 # 30 days

        # instruct the auto-trust-anchor-file probing to del anchors after ttl.
        # del-holddown: 2592000 # 30 days

        # auto-trust-anchor-file probing removes missing anchors after ttl.
        # If the value 0 is given, missing anchors are not removed.
        # keep-missing: 31622400 # 366 days

        # the amount of memory to use for the key cache.
        # plain value in bytes or you can append k, m or G. default is "4Mb". 
        # key-cache-size: 4m

        # the number of slabs to use for the key cache.
        # the number of slabs must be a power of 2.
        # more slabs reduce lock contention, but fragment memory usage.
        # key-cache-slabs: 4

        # the amount of memory to use for the negative cache (used for DLV).
        # plain value in bytes or you can append k, m or G. default is "1Mb". 
        # neg-cache-size: 1m

        # By default, for a number of zones a small default 'nothing here'
        # reply is built-in.  Query traffic is thus blocked.  If you
        # wish to serve such zone you can unblock them by uncommenting one
        # of the nodefault statements below.
        # You may also have to use domain-insecure: zone to make DNSSEC work,
        # unless you have your own trust anchors for this zone.
        # local-zone: "localhost." nodefault
        # local-zone: "127.in-addr.arpa." nodefault
        # 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." nodefault
        # local-zone: "10.in-addr.arpa." nodefault
        # local-zone: "16.172.in-addr.arpa." nodefault
        # local-zone: "17.172.in-addr.arpa." nodefault
        # local-zone: "18.172.in-addr.arpa." nodefault
        # local-zone: "19.172.in-addr.arpa." nodefault
        # local-zone: "20.172.in-addr.arpa." nodefault
        # local-zone: "21.172.in-addr.arpa." nodefault
        # local-zone: "22.172.in-addr.arpa." nodefault
        # local-zone: "23.172.in-addr.arpa." nodefault
        # local-zone: "24.172.in-addr.arpa." nodefault
        # local-zone: "25.172.in-addr.arpa." nodefault
        # local-zone: "26.172.in-addr.arpa." nodefault
        # local-zone: "27.172.in-addr.arpa." nodefault
        # local-zone: "28.172.in-addr.arpa." nodefault
        # local-zone: "29.172.in-addr.arpa." nodefault
        # local-zone: "30.172.in-addr.arpa." nodefault
        # local-zone: "31.172.in-addr.arpa." nodefault
        # local-zone: "168.192.in-addr.arpa." nodefault
        # local-zone: "0.in-addr.arpa." nodefault
        # local-zone: "254.169.in-addr.arpa." nodefault
        # local-zone: "2.0.192.in-addr.arpa." nodefault
        # local-zone: "100.51.198.in-addr.arpa." nodefault
        # local-zone: "113.0.203.in-addr.arpa." nodefault
        # local-zone: "255.255.255.255.in-addr.arpa." nodefault
        # local-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." nodefault
        # local-zone: "d.f.ip6.arpa." nodefault
        # local-zone: "8.e.f.ip6.arpa." nodefault
        # local-zone: "9.e.f.ip6.arpa." nodefault
        # local-zone: "a.e.f.ip6.arpa." nodefault
        # local-zone: "b.e.f.ip6.arpa." nodefault
        # local-zone: "8.b.d.0.1.0.0.2.ip6.arpa." nodefault
        # And for 64.100.in-addr.arpa. to 127.100.in-addr.arpa.
        
        # if unbound is running service for the local host then it is useful
        # to perform lan-wide lookups to the upstream, and unblock the
        # long list of local-zones above.  If this unbound is a dns server
        # for a network of computers, disabled is better and stops information
        # leakage of local lan information.
        # unblock-lan-zones: no

        # a number of locally served zones can be configured.
        #       local-zone: <zone> <type>
        #       local-data: "<resource record string>"
        # o deny serves local data (if any), else, drops queries. 
        # o refuse serves local data (if any), else, replies with error.
        # o static serves local data, else, nxdomain or nodata answer.
        # o transparent gives local data, but resolves normally for other names
        # o redirect serves the zone data for any subdomain in the zone.
        # o nodefault can be used to normally resolve AS112 zones.
        # o typetransparent resolves normally for other types and other names
        # o inform resolves normally, but logs client IP address
        #
        # defaults are localhost address, reverse for 127.0.0.1 and ::1
        # and nxdomain for AS112 zones. If you configure one of these zones
        # the default content is omitted, or you can omit it with 'nodefault'.
        # 
        # If you configure local-data without specifying local-zone, by
        # default a transparent local-zone is created for the data.
        #
        # You can add locally served data with
        # local-zone: "local." static
        # local-data: "mycomputer.local. IN A 192.0.2.51"
        # local-data: 'mytext.local TXT "content of text record"'
        #
        # You can override certain queries with
        # local-data: "adserver.example.com A 127.0.0.1"
        #
        # You can redirect a domain to a fixed address with
        # (this makes example.com, www.example.com, etc, all go to 192.0.2.3)
        # local-zone: "example.com" redirect
        # local-data: "example.com A 192.0.2.3"
        #
        # Shorthand to make PTR records, "IPv4 name" or "IPv6 name".
        # You can also add PTR records using local-data directly, but then
        # you need to do the reverse notation yourself.
        # local-data-ptr: "192.0.2.3 www.example.com"

        # service clients over SSL (on the TCP sockets), with plain DNS inside
        # the SSL stream.  Give the certificate to use and private key.
        # default is "" (disabled).  requires restart to take effect.
        # ssl-service-key: "path/to/privatekeyfile.key"
        # ssl-service-pem: "path/to/publiccertfile.pem"
        # ssl-port: 443

        # request upstream over SSL (with plain DNS inside the SSL stream).
        # Default is no.  Can be turned on and off with unbound-control.
        # ssl-upstream: no

        # DNS64 prefix. Must be specified when DNS64 is use.
        # Enable dns64 in module-config.  Used to synthesize IPv6 from IPv4.
        # dns64-prefix: 64:ff9b::0/96

# Python config section. To enable:
# o use --with-pythonmodule to configure before compiling.
# o list python in the module-config string (above) to enable.
# o and give a python-script to run.
python:
        # Script file to load
        # python-script: "@UNBOUND_SHARE_DIR@/ubmodule-tst.py"

# Remote control config section. 
remote-control:
        # Enable remote control with unbound-control(8) here.
        # set up the keys and certificates with unbound-control-setup.
        # control-enable: no

        # Set to no and use an absolute path as control-interface to use
        # a unix local named pipe for unbound-control.
        # control-use-cert: yes

        # what interfaces are listened to for remote control.
        # give 0.0.0.0 and ::0 to listen to all interfaces.
        # control-interface: 127.0.0.1
        # control-interface: ::1

        # port number for remote control operations.
        # control-port: 8953

        # unbound server key file.
        # server-key-file: "@UNBOUND_RUN_DIR@/unbound_server.key"

        # unbound server certificate file.
        # server-cert-file: "@UNBOUND_RUN_DIR@/unbound_server.pem"

        # unbound-control key file.
        # control-key-file: "@UNBOUND_RUN_DIR@/unbound_control.key"

        # unbound-control certificate file.
        # control-cert-file: "@UNBOUND_RUN_DIR@/unbound_control.pem"

# Stub zones.
# Create entries like below, to make all queries for 'example.com' and 
# 'example.org' go to the given list of nameservers. list zero or more 
# nameservers by hostname or by ipaddress. If you set stub-prime to yes, 
# the list is treated as priming hints (default is no).
# With stub-first yes, it attempts without the stub if it fails.
# stub-zone:
#       name: "example.com"
#       stub-addr: 192.0.2.68
#       stub-prime: no
#       stub-first: no
# stub-zone:
#       name: "example.org"
#       stub-host: ns.example.com.

# Forward zones
# Create entries like below, to make all queries for 'example.com' and
# 'example.org' go to the given list of servers. These servers have to handle
# recursion to other nameservers. List zero or more nameservers by hostname
# or by ipaddress. Use an entry with name "." to forward all queries.
# If you enable forward-first, it attempts without the forward if it fails.
# forward-zone:
#       name: "example.com"
#       forward-addr: 192.0.2.68
#       forward-addr: 192.0.2.73@5355  # forward to port 5355.
#       forward-first: no
# forward-zone:
#       name: "example.org"
#       forward-host: fwd.example.com