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Stubby

Stubby is the name given to a mode of using getdns which enables it to act as a local DNS-over-TLS stub resolver. It is recommended to use the latest release of the 1.1 version of getdns to have the most up to date version of Stubby.

In this mode  Stubby (getdns) does several things

  • Runs as a daemon
  • By default obtains its configuration information from the configuration file at /etc/stubby.conf
  • Can be configured to listen on the loopback address and send all outgoing DNS queries received on that address out over TLS to a DNS Privacy server
  • Can be configured with authentication information for DNS Privacy servers and instructed to use either a 'Strict' or an 'Opportunistic' Profile as described in Authentication and (D)TLS Profile for DNS-over-(D)TLS

Building Stubby

1.1. Dependencies

In this mode, the only dependency is OpenSSL (version 1.0.2 or later is required for hostname authentication to be supported). If this is installed in a non-standard location on your system use the --with-ssl option to configure below to specify where it is. 

1.1.1. Linux

It may be necessary to install 1.0.2 from source for most Linux distros.

1.1.2. OS X

It is recommended to install OpenSSL using homebrew, in which case use the following in the configure line in step 1.3 below:

--with-ssl=/usr/local/opt/openssl/

1.2. Download the getdns source

Either clone the code:

> git clone https://github.com/getdnsapi/getdns.git
> cd getdns
> git checkout release/1.1.0-alpha3

or grab a tarball from this page: Latest getdns releases

1.3. Build the code

> git submodule update --init
> libtoolize -ci
> autoreconf -fi
> mkdir build
> cd build
> ../configure --prefix=<install_location> --without-libidn --enable-stub-only
> make
> sudo make install

Logging/debugging

  • --enable-debug-daemon If you just want to see the connection statistics then use the --enable-debug-daemon option instead to the configure line above.
  • --enable-debug-stub If you want to see very detailed debug information as messages are processed (including connection statistics) then add the --enable-debug-stub option to the configure line above.

1.4. Create a config file

Stubby will use the config file at /etc/stubby.conf by default if it exists, or the config file location can be specified on the command line using the '-C' flag. [Note: With no config file stubby will use UDP to the default nameservers for queries).

Changes to the config file require a restart of Stubby.

The config file below is an example that will configure Stubby to:

  • listen on IPv4 and IPv6 on port 53 on the loopback address
  • use TLS over IPv4 to the NLnet labs test DNS Privacy Server for outgoing queries
  • enforce a 'Strict' Usage Profile based authentication of both a domain name and a SPKI pinset (If Opportunistic mode is desired, simply remove the 'tls_authentication: GETDNS_AUTHENTICATION_REQUIRED' field)
  • use an EDNS0 Keepalive timeout of 10s unless overridden by the server
{ resolution_type: GETDNS_RESOLUTION_STUB
, dns_transport_list: [ GETDNS_TRANSPORT_TLS ]
, upstream_recursive_servers:
  [ { address_data: 185.49.141.38
    , tls_auth_name: "getdnsapi.net"
    , tls_pubkey_pinset:
      [ { digest: "sha256"
        , value: 0x7e8c59467221f606695a797ecc488a6b4109dab7421aba0c5a6d3681ac5273d4
      } ]
   } ]
, tls_authentication: GETDNS_AUTHENTICATION_REQUIRED
, listen_addresses: [ 127.0.0.1, 0::1 ]
, idle_timeout: 10000
}

Additional privacy servers can be specified by adding more entries to the upstream_recursive_servers list above (note a separate entry must be made for the IPv4 and IPv6 addresses of a given server. More DNS Privacy test servers are listed here.

It is recommended to use more than one upstream for increased performance and reliability.

 

1.5. Run Stubby

Simply invoke Stubby on the command line. By default it runs in the foreground, the '-g' flag runs it in the background. The pid file is /var/run/stubby.pid

> sudo stubby

 

1.6. Test Stubby

A quick test can be done by using dig (or your favourite DNS tool) on the loopback address

> dig @127.0.0.1 www.example.com

1.7. Modify your upstream resolvers

Once this change is made your DNS queries will be re-directed to Stubby and sent over TLS! (You may need to restart some applications to have them pick up the network settings).

You can monitor the traffic using Wireshark watching on port 853.

For Stubby to re-send outgoing DNS queries over TLS the recursive resolvers configured on your machine must be changed to send all the local queries to the loopback interface on which Stubby is listening. This depends on the operating system being run. It is useful to note your existing default nameservers before making this change!

Linux/Unix systems

  • Edit the /etc/resolv.conf file
  • Comment out the existing nameserver entries
  • Add the following (only add the IPv4 address if you don't have IPv6)

    nameserver 127.0.0.1
    nameserver ::1

OS X

From the command line you can do the following to set the local DNS servers on, for example, your 'Wi-Fi' interface (first line clears all servers, second line adds localhost):

sudo networksetup -setdnsservers Wi-Fi Empty
sudo networksetup -setdnsservers Wi-Fi 127.0.0.1 ::1

If you want to reset, use something similar to the above to specify your default servers.

 

Or via the GUI:

  • Open System Preferences->Network->Advanced->DNS
  • Use the '-' button to remove the existing nameservers
  • Use the + button to add '127.0.0.1' and '::1' (only add the IPv4 address if you don't have IPv6)
  • Hit 'OK' in the DNS pane and then 'Apply' on the Network pane

Notes:

  • If you are using a DNS Privacy server that does not support concurrent processing of TLS queries, you may experience some issues due to timeouts causing subsequent queries on the same connection to fail.
  • Stubby currently backs-off for 1 hour from using servers that provide poor service - the next version will make this time configurable. Or this can be reset by restarting Stubby.

 

 

 


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