Unbound DNS Resolver

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Overview

Unbound is a validating, recursive and caching DNS resolver. It provides various modules so that DNSSEC (secure DNS) validation and stub-resolvers are possible.

On pfSense 2.2, Unbound has been integrated into the base system. Unbound is also the default DNS Resolver for new installations.

This page covers usage of Unbound in the base system of pfSense 2.2 and later. For its use as a package on pfSense 2.1.x, see Unbound package.

Configuration

To configure Unbound on pfSense 2.2, visit Services > DNS Resolver. By default the service is enabled for new installations. Systems upgraded from earlier versions of pfSense would have upgraded with the DNS Forwarder enabled.

Unbound requires that the DNS Forwarder be disabled or be moved to a different port. They provide the same functionality on the same port, so they cannot both bind to port 53 to provide DNS services.

  • Enable DNS Resolver: Enable or Disable the Unbound DNS Resolver daemon.
  • Network Interfaces: Interfaces used by Unbound for listening/binding. Default is to listen and respond to queries on all interfaces. The networks associated with the selected interfaces will automatically be added to an allowed list that can use Unbound for DNS queries. To allow other networks to query Unbound, use the Access Lists tab.
  • Outgoing Network Interfaces: Specific interface(s) to use for sourcing outbound queries. By default any interface may be used. Can be useful for selecting a specific WAN or local interface for VPN queries.
  • Enable DNSSEC Support: Uses DNSSEC to validate DNS queries. Be aware that it is recommended to disable forwarding and allow Unbound to handle all DNS resolution via root servers, which is the default behavior.
  • Enable Forwarding Mode: Controls whether Unbound will query root servers directly (unchecked, disabled) or if queries will be forwarded to the upstream DNS servers defined under System > General or those obtained by DHCP/PPPoE/etc (checked, enabled). Forwarding mode may be enabled if the upstream DNS servers are trusted and also provide DNSSEC support. Forwarding mode is necessary for Multi-WAN configurations unless default gateway switching is enabled.
  • Register DHCP leases in the DNS Resolver: DHCP static mappings can be registered in Unbound which enables the resolving of hostnames that have been assigned addresses by the DHCP server in pfSense. This should only be enabled on networks where the client hostnames can be trusted or controlled.
  • Register DHCP static mappings in the DNS Resolver: As above, but for static mappings.
  • TXT Comment support: Provides the ability to view comments associated with static host entries using DNS. To view these comments one would simply execute the following command:
host -t TXT host_entry <pfSense_ip>
  • Advanced: Text entry for advanced directives to be passed directly to Unbound.
If there are problems adding parameters such as
local-data: "click01.example.com A 10.10.10.1"

Place server: in line before that like this
server:
local-data: "click01.example.com A 10.10.10.1"

Unbound also supports DNS Rebinding Protections. To override these protections, Advanced options may be added to whitelist specific domains. See DNS Rebinding Protections for details.

Host Overrides allows creation of custom DNS responses/records to create new entries that do not exist in DNS outside the firewall, or to override DNS responses for other hosts.

Domain Overrides are for domains that should be queried by a specific remote server. For example, if all records for mysite.example.com exist on a private DNS server at 192.0.2.5, then a domain override can be set to forward all queries for that domain to that server.

Advanced Settings Tab

The Advanced option tab has additional useful settings, such as:

  • Configure the size of the message cache. The Message cache is used to store DNS Return Codes and validation statuses. The Resource Record Set cache size selected will automatically be set to twice the amount, which is used to store Resource Records data.

Access Lists Tab

When using specific interface bindings on the main tab, or when allowing queries across VPNs, Access Lists are needed to allow the clients to reach the DNS Resolver. Specific known-bad clients or networks could also be denied.

When editing an Access List entry, the following options are available:

  • Access List name: A name for reference.
  • Action: What to do with the queries that match this access list. Possible actions include:
    • Deny: Stops queries from hosts.
    • Refuse: Stops queries from hosts and sends a DNS rcode REFUSED error message back to the client. This is nicer to clients than Deny, but less secure since clients will know that a DNS server is present.
    • Allow: Allows queries from hosts within defined network.
    • Allow Snoop: Allows recursive and non-recursive access from hosts within the defined network. Used for cache snooping and ideally should only be configured for an administrative host for troubleshooting.
  • Networks: A list of Networks / CIDR masks, with a Description. These are the actual networks to use for matching this access list. Hosts that match these Networks will have the selected Action applied.
  • Description: A longer description of the access list for reference.

Additional Notes

Unbound provides various command line utilities to manage the DNS Cache server. The following control commands are currently not available in the webGUI but can be executed from the command line on a pfSense system.

To remove items from the cache:

  • unbound-control flush name - removes "name" from the cache all record types which include A, AAAA, NS< SOA, CNAME, DNAME, MX, PTR, SRV and NAPTR records.
  • unbound-control flush_type "name" "type" - removes the "name" and "type" from the cache where "type" is a particular record type.
  • unbound-control flush_zone "name" - removes all information at or below the name from cache. For example if .com is specified, all entries below .com will be removed. Note this process is slow as the entire cache needs to be inspected.

To determine the name servers that will be queried to lookup a zone:

  • unbound-control lookup "name"

Note: unbound in pfsense does not use the default conf file location, so will need tell it where it is.

  • unbound-control -c /var/unbound/unbound.conf command