Local resolver

Whalebone local resolver brings the advantage of visibility of local IP addresses that send the actual requests. Whalebone resolver is based on the implementation of Knot Resolver developed in the CZ.NIC labs.

System requirements

Local resolver is supported on dedicated (hardware or virtual) machine running a supported operating system.

  • Supported operating system (64-bit, server editions of following distributions):
    • Red Hat Enterprise Linux 7
    • CentOS 7
    • Debian 9
    • Ubuntu 16.04, 18.04
  • Supported filesystems
    • ext4
    • xfs only with d_type support (ftype=1)
  • Recommended hardware sizing for usual traffic (physical or virtual):
    • 2 CPU cores
    • 4 GB RAM
    • 40 GB HDD (at least 30 GB in /var partition)
  • Network setup requirements (local resolver needs the following ports opened):
    • TCP+UDP/53 into the internet destinations if responsible for the resolution
    • TCP/8443 to resolverapi.whalebone.io
    • TCP/443 to logger.whalebone.io, agentapi.whalebone.io, portal.whalebone.io, index.docker.io
    • Reachability of software repositories for the operating system


Without communication on port 8443 and 443 to the domains listed above the resolver won’t be installed at all (the installation script will abort).

With recommended hardware resources the resolver will provide stable and fast DNS resolution and filtering. Resolver can be run with significantly lower resources, but that is recommended just for low volume testing environments.


Should you need sizing estimation for large ISP or Enterprise network contact Whalebone. Whalebone local resolver will need approx. twice the RAM and CPU than usual resolver (BIND, Unbound).

Installation of a new resolver

In menu Resolvers press the button Create new. Choose a name (identifier) for your new resolver. The input is purely informative and won’t affect the functionality. Once you’ve entered the name, click Add resolver button After clicking the button an informative window will pop up with list of supported platforms and the one-line command for the installation. Copy the command and run on the machine dedicated for the local resolver. The command will run the installation script and will pass the one time token used for the resolver activation (the same command can not be used repeatedly).


Once the command is run the operating system is being checked and requirements installed. Script will inform you about the progress and it creates a detailed log named wb_install.log in current directory. Successul run of the installation script is ended with the notification `Final tuning of the OS` with value [ OK ]. Right after the installation also the initialization takes place and it could take several minutes before the resolver starts the services.



Local resolver is configured as an open resolver. It will respond to any request sent. This is quite comfortable in terms of availability of the services, but also could be a risk if the service is available from the outside networks. Please make sure you limit the access to the local resolver on port 53 (UDP and TCP) from the trusted networks only, otherwise it can be misused for various DoS attacks.

Security policies

The behavior of DNS filtering on the resolvers could be defined in the menu item Configuration and tab Security poicies. In the default state there is only the Default policy, which is automatically assigned to any new resolver. In any policy there are several options to be defined:

  • Malicious domains filtering
    • Allows to apply actions Audit (logging) or Block (redirect to blocking page) on resolution of malicious domains
    • Individual actions could be turned off - e.g. turn off the blocking for testing purposes
    • The slider values define the probability that the particular domain is malicious on the scale from 0 to 100 (0 is a safe domain, 100 is malicious)


The default threshold for blocking is set to 80 which is safe even for larger network with liberal policy towards the users. For more restrictive policy we suggest setting threshold for blocking to 70-75, in very restrictive networks even down to 60. Audit is purely informative, however setting the threshold too low can result in too many logged incidents.

  • Lists of blocked domains
    • Lists of domains, that has to be blocked
    • Such domains do not have to be malicious, it could be just domains blokced based on legal requirements
    • These lists are regularly updated by Whalebone
  • Whitelist
    • Domains that won’t be blocked at any time
    • The whitelist is applied to the domain and all of the subdomains, e.g.: whitelisted domain whalebone.io will also whitelist docs.whalebone.io, but not vice versa
  • Blacklist
    • Domains that will be blocked at all times (higher priority has only Whitelist)
    • The blacklist is applied to the domain and all of the subdomains, e.g.: whitelisted domain malware.ninja will also blacklist super.malware.ninja, but not vice versa


Changes will be applied to the resolvers in approx. 30 minutes. Saved configuration is used during preparation of the threat data package for the resolvers that download and apply those packages at regular intervals.

DNS resolution configuration

You can find the options to configure the resolver in the menu Configuration and tab DNS resolution. This page allows you to do the basic configuration without the knowledge of configuration syntax. Furthermore there is a text area allowing you to define any configuration to the underlying Knot Resolver.

Available configuration options:

  • Enable IPv6
    • Should the system has the IPv6 properly configured and working, it is possible to enable it. Otherwise the activation of IPv6 could have negative effects on the performance and latency of the resolver.
  • Forward queries to
    • This option allows to redirect all or chosen queries to upstream resolvers or authoritative DNS servers (suitable e.g. for forwarding to domain controllers of Active Directory)
    • Disable DNSSEC
      • If checked, the answers from the forwarded queries won’t be DNSSEC validated. We recommend to check this option should the upstream server have not DNSSEC configured properly.
    • All queries to
      • Option to forward all queries to one or more resolver
    • Following domains
      • Option to choose particular domains that should be forwarded to on more resolvers
      • Different resolvers could be defined for different domains
  • Static records
    • Predefined answers that should be returned for particular domains
    • Could serve for special purposes such as monitoring or very simple substition of records on authoritative server
  • Advanced DNS configuration

Resolver management

On the Resolvers page there is an overview of created resolvers. Administrator can adjust the configuration, deploy updates and install new resolvers.

Resolvers overview

In the main resolver overview there are tiles with resolver details and configuration options. The overview includes information about operating system and resources as CPU, Memory and HDD usage. Therre is also the state of services running on the resolvers (should state “Running” if everything is OK) and the status of the communication channel between the resolver and the cloud (it is expected to be “Active”).

Deploy configuration

Should you change any configuration related to the DNS resolution, you have to deploy the configuration afterwards. If there are any configuration changes available to be deployed, there will be a red icon with down right arrow visible on the resolver card. Once clicked, the webpage will ask for confirmation and the successful deployment will be notified in the top right corner.


If the result is an deployment error, try to repeat the action. The reason for the error could be a short term communication outage between the cloud and the resolver.


Knot Resolver - Tips & Tricks

Advanced configuration of Whalebone resolver allows to apply any Knot Resolver configuration. In this section we are going to describe the most frequent use cases and examples of such configuration snippets. Views, policies and their actions are evaluated in the sequence as they are defined (except special chain actions that are described in the official Knot Resolver documentation). First match will execute the action, the rest of the policy rules is not evaluated. If you are going to combine different configuration snnippets, you can load the same module just once at the beginning of the configuration.

Allow particular IP ranges

Define a list of IP ranges that will be allowed to use this DNS resolver. Queries from all other ranges will be refused.

-- load modules
modules = {'policy', 'view'}

--define list of ranges to allow
allowed = {

-- allow list of ranges
for i,subnet in ipairs(allowed) do
  view:addr(subnet, policy.all(policy.PASS))

-- block all other ranges
view:addr('', policy.all(policy.DENY))

Refuse particular IP ranges

Define a list of IP ranges that will be blocked to use this DNS resolver. Queries from all other ranges will be allowed.

-- load modules
modules = {'policy', 'view'}

--define list of ranges to block
blocked = {

-- block list of ranges
for i,subnet in ipairs(blocked) do
  view:addr(subnet, policy.all(policy.REFUSE))

Allow list of domains

-- load modules
modules = {'policy'}

--define list of allowed domains
domains = {

-- allow list of domains
for i,domain in ipairs(domains) do
  policy.suffix(policy.PASS, {todname(domain)})

Disable DNSSEC globally

trust_anchors.negative = { '.' }

Outgoing IP address