Advanced Pi-hole Config: Recursive DNS With Unbound

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This is an advanced configuration not because it’s particularly difficult to implement, but because it’s not necessary for your Pi-hole system to function properly. For those who would prefer to not rely on third party DNS providers – whether for privacy reasons or just because you can – configuring your Pi-hole system with Unbound for recursive DNS takes only a few minutes to setup and configure.

Before We Begin

A few things we need to address before we begin.

Assumptions

This tutorial assumes that you’ve already got a working Pi-hole installation on either a Debian or Ubuntu based server and that you know how to access the terminal on that server. If you need instructions on installing Pi-hole, please refer to the series index at the top of the page.

Installing Packages

Let’s begin with ensuring our server’s packages are up to date.

sudo apt update && sudo apt upgrade -y

Next, let’s install our recursive DNS resolver, Unbound.

sudo apt install unbound -y

Once the software has completed installing, next up is configuring Unbound.

Configure Unbound

To configure Unbound, we need to create it’s config file. Start by copying the contents we need to put into the file into your clipboard. I’ve provided the config file contents below – I obtained it from the Pi-hole website.

server:
    # If no logfile is specified, syslog is used
    # logfile: "/var/log/unbound/unbound.log"
    verbosity: 0

    interface: 127.0.0.1
    port: 5335
    do-ip4: yes
    do-udp: yes
    do-tcp: yes

    # May be set to yes if you have IPv6 connectivity
    do-ip6: no

    # You want to leave this to no unless you have *native* IPv6. With 6to4 and
    # Terredo tunnels your web browser should favor IPv4 for the same reasons
    prefer-ip6: no

    # Use this only when you downloaded the list of primary root servers!
    # If you use the default dns-root-data package, unbound will find it automatically
    #root-hints: "/var/lib/unbound/root.hints"

    # Trust glue only if it is within the server's authority
    harden-glue: yes

    # Require DNSSEC data for trust-anchored zones, if such data is absent, the zone becomes BOGUS
    harden-dnssec-stripped: yes

    # Don't use Capitalization randomization as it known to cause DNSSEC issues sometimes
    # see https://discourse.pi-hole.net/t/unbound-stubby-or-dnscrypt-proxy/9378 for further details
    use-caps-for-id: no

    # Reduce EDNS reassembly buffer size.
    # IP fragmentation is unreliable on the Internet today, and can cause
    # transmission failures when large DNS messages are sent via UDP. Even
    # when fragmentation does work, it may not be secure; it is theoretically
    # possible to spoof parts of a fragmented DNS message, without easy
    # detection at the receiving end. Recently, there was an excellent study
    # >>> Defragmenting DNS - Determining the optimal maximum UDP response size for DNS <<<
    # by Axel Koolhaas, and Tjeerd Slokker (https://indico.dns-oarc.net/event/36/contributions/776/)
    # in collaboration with NLnet Labs explored DNS using real world data from the
    # the RIPE Atlas probes and the researchers suggested different values for
    # IPv4 and IPv6 and in different scenarios. They advise that servers should
    # be configured to limit DNS messages sent over UDP to a size that will not
    # trigger fragmentation on typical network links. DNS servers can switch
    # from UDP to TCP when a DNS response is too big to fit in this limited
    # buffer size. This value has also been suggested in DNS Flag Day 2020.
    edns-buffer-size: 1232

    # Perform prefetching of close to expired message cache entries
    # This only applies to domains that have been frequently queried
    prefetch: yes

    # One thread should be sufficient, can be increased on beefy machines. In reality for most users running on small networks or on a single machine, it should be unnecessary to seek performance enhancement by increasing num-threads above 1.
    num-threads: 1

    # Ensure kernel buffer is large enough to not lose messages in traffic spikes
    so-rcvbuf: 1m

    # Ensure privacy of local IP ranges
    private-address: 192.168.0.0/16
    private-address: 169.254.0.0/16
    private-address: 172.16.0.0/12
    private-address: 10.0.0.0/8
    private-address: fd00::/8
    private-address: fe80::/10

This config has Unbound operating using port 5335. We’ll need this information later.

Next up, let’s create the config file using the nano editor.

sudo nano /etc/unbound/unbound.conf.d/pi-hole.conf

With nano open, paste the config file contents then press CTRL + X and then enter when prompted to save the file and exit nano.

Now we need to restart unbound for the new configuration to take effect.

sudo systemctl restart unbound

You can check the status of Unbound to ensure it’s working properly with this command.

sudo systemctl status unbound

We have one step left now – updating our Pi-hole upstream DNS settings.

Update Pi-hole DNS Settings

Log into your Pi-hole and go to the DNS tab on the Settings page. Uncheck all Upstream DNS Servers in the left column and enter 127.0.0.1#5335 under Custom 1 in the right column. Remember earlier I mentioned we’d need to know that Unbound was using port 5335?

Once you’ve made the changes, scroll down and click Save.

Pi-hole Recursive DNS with Unbound - Upstream DNS Settings
Pi-hole Recursive DNS with Unbound – Upstream DNS Settings

Conclusion

And that’s all there is to it! Your Pi-hole setup will now make it’s own recursive DNS queries instead of relying upon a 3rd party DNS provider. If you found this article helpful or have any questions, I encourage you to please share this article with others and/or leave a comment below. Thanks for reading and I hope you visit again soon!

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