Unbound DNS

Unbound is a validating, recursive, caching DNS resolver. It is designed to be fast and lean and incorporates modern features based on open standards.

Since OPNsense 17.7 it has been our standard DNS service, which on a new install is enabled by default.

General settings

Below you will find the most relevant settings from the General menu section.


Enable our DNS resolver

Listen Port

Port to listen on, when blank, the default (53) is used.

Network Interfaces

Interface IP addresses used for responding to queries from clients. If an interface has both IPv4 and IPv6 IPs, both are used. Queries to other interface IPs not selected are discarded. The default behavior is to respond to queries on every available IPv4 and IPv6 address.


Enable DNSSEC to use digital signatures to validate results from upstream servers and mitigate against cache poisoning.


Enable DNS64 so IPv6-only clients can reach IPv4-only servers. If enabled, Unbound synthesizes AAAA records for domains which only have A records. DNS64 requires NAT64 to be useful, e. g. the Tayga plugin or a third-party NAT64 service. The DNS64 prefix must match the IPv6 prefix used be the NAT64.

AAAA-only mode

If this option is set, Unbound will remove all A records from the answer section of all responses.

Register ISC DHCP4 Leases

IPv4 only If this option is set, then machines that specify their hostname when requesting a DHCP lease will be registered in Unbound, so that their names can be resolved.

The source of this data is client-hostname in the dhcpd.leases file. This can also be inspected using the Leases page.

DHCP Domain Override

When the above registrations shouldn’t use the same domain name as configured on this firewall, you can specify a different one here.

Register ISC DHCP Static Mappings

Register static dhcpd entries so clients can resolve them. Supported on IPv4 and IPv6.

No IPv6 Link-local aaddresses

Do not register link local addresses for IPv6. This will prevent the return of unreachable addresses when more than one listen interface is configured.

System A/AAAA records

If this option is set, then no A/AAAA records for the configured listen interfaces will be generated. This also means that no PTR records will be created. If desired, you can manually add A/AAAA records in Overrides. Use this to control which interface IP addresses are mapped to the system host/domain name as well as to restrict the amount of information exposed in replies to queries for the system host/domain name.

TXT Comment Support

Register descriptions as comments for dhcp static host entries.

Local Zone Type

The local zone type used for the system domain. Type descriptions are available under “local-zone:” in the unbound.conf(5) manual page. The default is ‘transparent’.


In order for the client to query unbound, there need to be an ACL assigned in Services ‣ Unbound DNS ‣ Access Lists. The configured interfaces should gain an ACL automatically. If the client address is not in any of the predefined networks, please add one manually.


Within the overrides section you can create separate host definition entries and specify if queries for a specific domain should be forwarded to a predefined server.

Host override settings

Host overrides can be used to change DNS results from client queries or to add custom DNS records. PTR records are also generated under the hood to support reverse DNS lookups. These are generated in the following way:

  • If System A/AAAA records in General settings is unchecked, a PTR record is created for the primary interface.

  • Each host override entry that does not include a wildcard for a host, is assigned a PTR record.

  • If a host override entry includes a wildcard for a host, the first defined alias is assigned a PTR record.

  • Every other alias does not get a PTR record.


Name of the host, without domain part. Use “*” to create a wildcard entry.


Domain of the host (such as example.com)


Record type, A or AAA (IPv4 or IPv6 address), MX to define a mail exchange


Address of the host


User readable description, only for informational purposes


Copies of the above data for different hosts


You may create alternative names for a Host. E.g. when having a webserver with several virtual hosts you create a Host override entry with the IP and name for the webserver and an alias name for every virtual host on this webserver.

You have to select the host in the top list and it will the show you the assigned aliases in the bottom list.

Domain override settings

Domain overrides can be used to forward queries for specific domains (and subsequent subdomains) to local or remote DNS servers.


Domain overrides has been superseded by Query Forwarding. Query forwarding also allows you to forward every single request.


Domain to override

IP address

IP address of the authoritative DNS server for this domain


User readable description, only for informational purposes


Although the default settings should be reasonable for most setups, some need more tuning or require specific options set. Some of these settings are enabled and given a default value by Unbound, refer to unbound.conf(5) for the defaults.

Hide Identity

If enabled, id.server and hostname.bind queries are refused.

Hide Version

If enabled version.server and version.bind queries are refused.

Prefetch Support

Message cache elements are prefetched before they expire to help keep the cache up to date. When enabled, this option can cause an increase of around 10% more DNS traffic and load on the server, but frequently requested items will not expire from the cache.

Prefetch DNS Key Support

DNSKEY’s are fetched earlier in the validation process when a Delegation signer is encountered. This helps lower the latency of requests but does utilize a little more CPU.

Harden DNSSEC data

DNSSEC data is required for trust-anchored zones. If such data is absent, the zone becomes bogus. If this is disabled and no DNSSEC data is received, then the zone is made insecure.

Serve expired responses

Serve expired responses from the cache with a TTL of 0 without waiting for the actual resolution to finish. When checked, multiple options to customize the behaviour regarding expired responses will appear.

Expired Record Reply TTL Value

TTL value to use when replying with expired data. If “Client Expired Response Timeout” is also used then it is recommended to use 30 as the default value as per RFC 8767. Only applicable when “Serve expired responses” is checked.

TTL for Expired Responses

Limits the serving of expired responses to the configured amount of seconds after expiration. A value of 0 disables the limit. A suggested value as per RFC 8767 is between 86400 (1 day) and 259200 (3 days). Only applicable when “Serve expired responses” is checked.

Reset Expired Record TTL

Set the TTL of expired records to the “TTL for Expired Responses” value after a failed attempt to retrieve the record from an upstream server. This makes sure that the expired records will be served as long as there are queries for it. Only applicable when “Serve expired responses” is checked.

Client Expired Response Timeout

Time in milliseconds before replying to the client with expired data. This essentially enables the serve- stable behavior as specified in RFC 8767 that first tries to resolve before immediately responding with expired data. A recommended value per RF 8767 is 1800. Setting this to 0 will disable this behavior. Only applicable when “Serve expired responses” is checked.

Strict QNAME Minimisation

Send minimum amount of information to upstream servers to enhance privacy. 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.

Extended Statistics

If enabled, extended statistics are printed to syslog.

Log Queries

If enabled, prints one line per query to the log, with the log timestamp and IP address, name, type and class. Note that it takes time to print these lines, which makes the server (significantly) slower. Odd (non-printable) characters in names are printed as ‘?’.

Log Replies

If enabled, prints one line per reply to the log, with the log timestamp and IP address, name, type, class, return code, time to resolve, whether the reply is from the cache and the response size. Note that it takes time to print these lines, which makes the server (significantly) slower. Odd (non-printable) characters in names are printed as ‘?’.

Tag Queries and Replies

If enabled, prints the word ‘query: ‘ and ‘reply: ‘ with logged queries and replies. This makes filtering logs easier.

Log level verbosity

Select the log verbosity. 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.

Private Domains

List of domains to mark as private. These domains and all its subdomains are allowed to contain private addresses.

Rebind Protection networks

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. (Only applicable when DNS rebind check is enabled in Administration)

Insecure Domains

List of domains to mark as insecure. DNSSEC chain of trust is ignored towards the domain name.

Message Cache Size

Size of the message cache. The message cache stores DNS rcodes and validation statuses. The RRSet cache (which contains the actual RR data) will automatically be set to twice this amount. Valid input is plain bytes, optionally appended with ‘k’, ‘m’, or ‘g’ for kilobytes, megabytes or gigabytes respectively.

RRset Cache Size

Size of the RRset cache. Contains the actual RR data. Valid input is plain bytes, optionally appended with ‘k’, ‘m’, or ‘g’ for kilobytes, megabytes or gigabytes respectively. Automatically set to twice the amount of the Message Cache Size when empty, but can be manually modified.

Outgoing TCP Buffers

The number of outgoing TCP buffers to allocate per thread. If 0 is selected then no TCP queries to authoritative servers are done.

Incoming TCP Buffers

The number of incoming TCP buffers to allocate per thread. If 0 is selected then no TCP queries from clients are accepted.

Number of queries per thread

The number of queries that every thread will service simultaneously. If more queries arrive that need to be serviced, and no queries can be jostled out (see “Jostle Timeout”), then these queries are dropped. This forces the client to resend after a timeout, allowing the server time to work on the existing queries.

Outgoing Range

The number of ports to open. This number of file descriptors can be opened per thread. Larger numbers need extra resources from the operating system. For performance a very large value is best. For reference, usually double the amount of queries per thread is used.

Jostle Timeout

This timeout is used for when the server is very busy. Set to a value that usually results in one round-trip 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.

Maximum TTL for RRsets and messages

Configure a maximum Time to live in seconds for RRsets and messages in the cache. When the internal TTL expires the cache item is expired. This can be configured to force the resolver to query for data more often and not trust (very large) TTL values.

Minimum TTL for RRsets and messages

Configure a minimum Time to live in seconds for RRsets and messages in the cache. If the minimum value kicks in, the data is cached for longer than the domain owner intended, and thus fewer queries are made to look up the data. The 0 value ensures the data in the cache is as the domain owner intended. High values can lead to trouble as the data in the cache might not match up with the actual data anymore.

TTL for Host cache entries

Time to live in seconds for entries in the host cache. The host cache contains round-trip timing, lameness and EDNS support information.

Keep probing down hosts

Keep probing hosts that are down in the infrastructure host cache. Hosts that are down are probed about every 120 seconds with an exponential backoff. If hosts do not respond within this time period, they are marked as down for the duration of the host cache TTL. This setting can be used in conjunction with “TTL for Host cache entries” to increase responsiveness if internet connectivity bounces happen frequently.

Number of Hosts to cache

Number of hosts for which information is cached.

Unwanted Reply Threshold

If enabled, 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 file. This defensive action is to clear the RRSet and message caches, hopefully flushing away any poison.

Access Lists

Access lists define which clients may query our dns resolver. Records for the assigned interfaces will be automatically created and are shown in the overview. You can also define custom policies, which apply an action to predefined networks.


The action can be as defined in the list below. The most specific netblock match is used, if none match deny is used. The order of the access-control statements therefore does not matter.



This action stops queries from hosts within the defined networks.


This action also stops queries from hosts within the defined networks, but sends a DNS rcode REFUSED error message back to the client.


This action allows queries from hosts within the defined networks.

Allow Snoop

This action allows recursive and nonrecursive access from hosts within the defined networks. Used for cache snooping and ideally should only be configured for your administrative host.

Deny Non-local

Allow only authoritative local-data queries from hosts within the defined networks. Messages that are disallowed are dropped.

Refuse Non-local

Allow only authoritative local-data queries from hosts within the defined networks. Sends a DNS rcode REFUSED error message back to the client for messages that are disallowed.


Enable integrated dns blacklisting using one of the predefined sources or custom locations.


Enable blacklists

Enable SafeSearch

Force the usage of SafeSearch on Google, DuckDuckGo, Bing, Qwant, PixaBay and YouTube.

Type of DNSBL

Predefined external sources

URLs of Blacklists

Additional http[s] location to download blacklists from, only plain text files containing a list of fqdn’s (e.g. my.evil.domain.com) OR wildcard domains (e.g. *.my.evil.domain.com) are supported.

Whitelist Domains

When a blacklist item contains a pattern defined in this list it will be ommitted from the results. e.g. .*.nl would exclude all .nl domains. Blocked domains explicitly whitelisted using the Reporting: Unbound DNS page will show up in this list.

Blocklist Domains

List of domains to explicitly block. Regular expressions are not supported. Passed domains explicitly blocked using the Reporting: Unbound DNS page will show up in this list.

Wildcard Domains

List of wildcard domains to blocklist. All subdomains of the given domain will be blocked. Blocking first-level domains (e.g. ‘com’) is not supported.

Destination Address

Specify an IP address to return when DNS records are blocked. Can be used to redirect such domains to a separate webserver informing the user that the content has been blocked. The default is Any value in this field is skipped if “Return NXDOMAIN” is checked.


Instead of returning the “Destination Address”, return the DNS return code “NXDOMAIN”. This is useful in cases where devices cannot cope with the destination address, such as certain Apple devices.


Applying the blocklist settings will not restart Unbound, rather it will signal to Unbound to dynamically process the blocklists as soon as they’re downloaded. There may be up to a minute of delay before Unbound has loaded everything. During this time Unbound will still be just as responsive.

When any of the DNSBL types are used, the content will be fetched directly from its original source, to get a better understanding of the source of the lists we compiled the list below containing references to the list maintainers.

Predefined sources

Abuse.ch - ThreatFox IOC database


AdAway List


AdGuard List


OISD - Domain Blocklist Ads*


OISD - Domain Blocklist Big*


OISD - Domain Blocklist NSFW*








NoCoin List


PornTop1M List


Simple Ad List


Simple Tracker List






YoYo List



The OISD lists are wildcard lists. Meaning that they will block all subdomains of the listed domains. For more information, refer to OISD. This keeps the list small and manageable, but are more effective than regular lists.


In order to automatically update the lists on timed intervals you need to add a cron task, just go to System -> Settings ->Cron and a new task for a command called “Update Unbound DNSBLs”.

Usually once a day is a good enough interval for these type of tasks.

Query Forwarding

The Query Forwarding section allows for entering arbitrary nameservers to forward queries to. It is assumed that the nameservers entered here are capable of handling further recursion for any query. In this section you are able to specify nameservers to forward to for specific domains queried by clients, catch all domains and specify nondefault ports.

Use System Nameservers

The configured system nameservers will be used to forward queries to. This will override any entry made in the custom forwarding grid, except for entries targeting a specific domain. If there are no system nameservers, you will be prompted to add one in General. If you expected a DNS server from your WAN and it’s not listed, make sure you set “Allow DNS server list to be overridden by DHCP/PPP on WAN” there as well.


Do not use the system nameservers option if you have a multi-WAN setup and have Unbound running alongside multiple DNS servers configured in General with separate gateways assigned to them. Unbound will use the locally created routes to reach the system nameservers, which will not work when the gateway is down.


Keep in mind that if the “Use System Nameservers” checkbox is checked, the system nameservers will be preferred over any catch-all entry in both Query Forwarding and DNS-over-TLS, this means that entries with a specific domain will still be forwarded to the specified nameserver.


Enable query forwarding for this domain.


Domain of the host. All queries for this domain will be forwarded to the nameserver specified in “Server IP”. Leave empty to catch all queries and forward them to the nameserver.

Server IP

Address of the DNS server to be used for recursive resolution.


Specify the port used by the DNS server. Default is port 53. Useful when configuring e.g. DNSCrypt-Proxy


Be careful enabling “DNS Query Forwarding” in combination with DNSSEC, no DNSSEC validation will be performed for forwards with a specific domain, as the upstream server might be a local controller. If forwarding everything and the upstream server doesn’t support DNSSEC, its answers will not reach the client as no DNSSEC validation could be performed.

DNS over TLS

DNS over TLS uses the same logic as Query Forwarding, except it uses TLS for transport.


Please be aware of interactions between Query Forwarding and DNS over TLS. Since the same principle as Query Forwarding applies, a catch-all entry specified in both sections will be considered a duplicate zone. In our case DNS over TLS will be preferred.


Enable DNS over TLS for this domain.


Domain of the host. All queries for this domain will be forwarded to the nameserver specified in “Server IP”. Leave empty to catch all queries and forward them to the nameserver.

Server IP

Address of the DNS server to be used for recursive resolution.


Specify the port used by the DNS server. Always enter port 853 here unless there is a good reason not to, such as when using an SSH tunnel.

Verify CN

The name to use for certificate verification, e.g. “445b9e.dns.nextdns.io”. Used by Unbound to check the TLS authentication certificates. It is strongly discouraged to omit this field since man-in-the-middle attacks will still be possible.


To ensure a validated environment, it is a good idea to block all outbound DNS traffic on port 53 using a firewall rule when using DNS over TLS. Should clients query other nameservers directly themselves, a NAT redirect rule to (the local Unbound service) can be used to force these requests over TLS.

Public Resolvers

Hosted by

Server IP

Server Port

Verify CN

















The statistics page provides some insights into the running server, such as the number of queries executed, cache usage and uptime.

Advanced Configurations

Some installations require configuration settings that are not accessible in the UI. To support these, individual configuration files with a .conf extension can be put into the /usr/local/etc/unbound.opnsense.d directory. These files will be automatically included by the UI generated configuration. Multiple configuration files can be placed there. But note that

  • As it cannot be predicted in which clause the configuration currently takes place, you must prefix the configuration with the required clause. For the concept of “clause” see the unbound.conf(5) documentation.

  • The wildcard include processing in Unbound is based on glob(7). So the order in which the files are included is in ascending ASCII order.

  • Name collisions with plugin code, which use this extension point e. g. dnsbl.conf, may occur. So be sure to use a unique filename.

  • It is a good idea to check the complete configuration via:

    # check if the resulting configuration is valid
    configctl unbound check

    This will report errors that prevent Unbound from starting and also list warnings that may give hints as to why a particular configuration is not working or how it could be improved.

This is a sample configuration file to add an option in the server clause:

  private-domain: xip.io


As a more permanent solution the template system (“Using Templates”) can be used to automatically generate these files.

To get the same effect as placing the file in the sample above directly in /usr/local/etc/unbound.opnsense.d follow these steps:

  1. Create a +TARGETS file in /usr/local/opnsense/service/templates/sampleuser/Unbound:

  2. Place the template file as sampleuser_additional_options.conf in the same directory:

      private-domain: xip.io
  3. Test the template generation by issuing the following command:

    # generate template
    configctl template reload sampleuser/Unbound
  4. Check the output in the target directory:

    # show generated file
    cat /usr/local/etc/unbound.opnsense.d/sampleuser_additional_options.conf
    # check if configuration is valid
    configctl unbound check


It is the sole responsibility of the administrator which places a file in the extension directory to ensure that the configuration is valid.


This method replaces the Custom options settings in the General page of the Unbound configuration, which was removed in version 21.7.