diff --git a/pi-hole/unbound/readme.md b/pi-hole/unbound/readme.md new file mode 100644 index 0000000..30465a0 --- /dev/null +++ b/pi-hole/unbound/readme.md @@ -0,0 +1,270 @@ +

unbound

+ +

Pi-hole as All-Around DNS Solution

+

The problem: Whom can you trust?

+

Pi-hole includes a caching and forwarding DNS server, now known as FTLDNS. After applying the blocking lists, it forwards requests made by the clients to configured upstream DNS server(s). However, as has been mentioned by several users in the past, this leads to some privacy concerns as it ultimately raises the question: Whom can you trust? Recently, more and more small (and not so small) DNS upstream providers have appeared on the market, advertising free and private DNS service, but how can you know that they keep their promises? Right, you can't.

+

Furthermore, from the point of an attacker, the DNS servers of larger providers are very worthwhile targets, as they only need to poison one DNS server, but millions of users might be affected. Instead of your bank's actual IP address, you could be sent to a phishing site hosted on some island. This scenario has already happened and it is likely to happen again...

+

When you operate your own (tiny) recursive DNS server, then the likeliness of getting affected by such an attack is greatly reduced.

+

What is a recursive DNS server?

+

The first distinction we have to be aware of is whether a DNS server is authoritative or not. If I'm the authoritative server for, e.g., pi-hole.net, then I know which IP is the correct answer for a query. Recursive name servers, in contrast, resolve any query they receive by consulting the servers authoritative for this query by traversing the domain. +Example: We want to resolve pi-hole.net. On behalf of the client, the recursive DNS server will traverse the path of the domain across the Internet to deliver the answer to the question.

+

What does this guide provide?

+

In only a few simple steps, we will describe how to set up your own recursive DNS server. It will run on the same device you're already using for your Pi-hole. There are no additional hardware requirements.

+

This guide assumes a fairly recent Debian/Ubuntu-based system and will use the maintainer provided packages for installation to make it an incredibly simple process. It assumes only a very basic knowledge of how DNS works.

+

A standard Pi-hole installation will do it as follows:

+
    +
  1. Your client asks the Pi-hole Who is pi-hole.net?
    2. +
  2. Your Pi-hole will check its cache and reply if the answer is already known.
    3. +
  3. Your Pi-hole will check the blocking lists and reply if the domain is blocked.
    4. +
  4. Since neither 2. nor 3. is true in our example, the Pi-hole forwards the request to the configured external upstream DNS server(s).
    5. +
  5. Upon receiving the answer, your Pi-hole will reply to your client and tell it the answer to its request.
    6. +
  6. Lastly, your Pi-hole will save the answer in its cache to be able to respond faster if any of your clients queries the same domain again.
    7. +
+

After you set up your Pi-hole as described in this guide, this procedure changes notably:

+
    +
  1. Your client asks the Pi-hole Who is pi-hole.net?
    2. +
  2. Your Pi-hole will check its cache and reply if the answer is already known.
    3. +
  3. Your Pi-hole will check the blocking lists and reply if the domain is blocked.
    4. +
  4. Since neither 2. nor 3. is true in our example, the Pi-hole delegates the request to the (local) recursive DNS resolver.
    5. +
  5. Your recursive server will send a query to the DNS root servers: "Who is handling .net?"
    6. +
  6. The root server answers with a referral to the TLD servers for .net.
    7. +
  7. Your recursive server will send a query to one of the TLD DNS servers for .net: "Who is handling pi-hole.net?"
    8. +
  8. The TLD server answers with a referral to the authoritative name servers for pi-hole.net.
    9. +
  9. Your recursive server will send a query to the authoritative name servers: "What is the IP of pi-hole.net?"
    10. +
  10. The authoritative server will answer with the IP address of the domain pi-hole.net.
    11. +
  11. Your recursive server will send the reply to your Pi-hole which will, in turn, reply to your client and tell it the answer to its request.
    12. +
  12. Lastly, your Pi-hole will save the answer in its cache to be able to respond faster if any of your clients queries the same domain again.
    13. +
+

You can easily imagine even longer chains for subdomains as the query process continues until your recursive resolver reaches the authoritative server for the zone that contains the queried domain name. It is obvious that the methods are very different and the own recursion is more involved than "just" asking some upstream server. This has benefits and drawbacks:

+ +

Setting up Pi-hole as a recursive DNS server solution

+

We will use unbound, a secure open-source recursive DNS server primarily developed by NLnet Labs, VeriSign Inc., Nominet, and Kirei. +The first thing you need to do is to install the recursive DNS resolver:

+
sudo apt install unbound
+
+

If you are installing unbound from a package manager, it should install the root.hints file automatically with the dependency dns-root-data. The root hints will then be automatically updated by your package manager.

+

Optional: Download the current root hints file (the list of primary root servers which are serving the domain "." - the root domain). Update it roughly every six months. Note that this file changes infrequently. This is only necessary if you are not installing unbound from a package manager. If you do this optional step, you will need to uncomment the root-hints: configuration line in the suggested config file.

+
wget https://www.internic.net/domain/named.root -qO- | sudo tee /var/lib/unbound/root.hints
+
+

Configure unbound

+

Highlights:

+ +

(Note that for some Red Hat based distros including CentOS up to v10, the path for the pi-hole.conf file may be /etc/unbound/conf.d/pi-hole.conf)

+
/etc/unbound/unbound.conf.d/pi-hole.conf
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 no if you don't have IPv6 connectivity
+    do-ip6: yes
+
+    # 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
+
+    # Ensure no reverse queries to non-public IP ranges (RFC6303 4.2)
+    private-address: 192.0.2.0/24
+    private-address: 198.51.100.0/24
+    private-address: 203.0.113.0/24
+    private-address: 255.255.255.255/32
+    private-address: 2001:db8::/32
+
+

Start your local recursive server and test that it's operational:

+
sudo service unbound restart
+dig pi-hole.net @127.0.0.1 -p 5335
+
+

The first query may be quite slow, but subsequent queries, also to other domains under the same TLD, should be fairly quick.

+

Test validation

+

You can test DNSSEC validation using

+
dig fail01.dnssec.works @127.0.0.1 -p 5335
+dig +ad dnssec.works @127.0.0.1 -p 5335
+
+

The first command should give a status report of SERVFAIL and no IP address. The second should give NOERROR plus an IP address in addition to a ad in the flags: section. The ad signifies (Authentic Data), indicating the DNS response has been authenticated and validated using DNSSEC.

+

Configure Pi-hole

+

Finally, configure Pi-hole to use your recursive DNS server by specifying 127.0.0.1#5335 in the Settings > DNS > Custom DNS servers section and ensuring that all the other upstream servers are unticked, as shown below:

+

Upstream DNS Servers Configuration

+

Don't forget to click on the Save & Apply button.

+

Disable resolvconf.conf entry for unbound (Required for Debian Bullseye+ releases)

+

Debian Bullseye+ releases auto-install a package called openresolv with a certain configuration that will cause unexpected behaviour for pihole and unbound. The effect is that the unbound-resolvconf.service instructs resolvconf to write unbound's own DNS service at nameserver 127.0.0.1 , but without the 5335 port, into the file /etc/resolv.conf. That /etc/resolv.conf file is used by local services/processes to determine DNS servers configured. You need to edit the configuration file and disable the service to work-around the misconfiguration.

+

Step 1 - Disable the Service

+

To check if this service is enabled for your distribution, run below one. It will show either active or inactive or it might not even be installed resulting in a could not be found message:

+
systemctl is-active unbound-resolvconf.service
+
+

To disable the service, run the statement below:

+
sudo systemctl disable --now unbound-resolvconf.service
+
+

Step 2 - Disable the file resolvconf_resolvers.conf

+

Disable the file resolvconf_resolvers.conf from being generated when resolvconf is invoked elsewhere.

+
sudo sed -Ei 's/^unbound_conf=/#unbound_conf=/' /etc/resolvconf.conf
+sudo rm /etc/unbound/unbound.conf.d/resolvconf_resolvers.conf
+
+

Restart unbound.

+
sudo service unbound restart
+
+

Add logging to unbound

+
+

Warning

+

It's not recommended to increase verbosity for daily use, as unbound logs a lot. But it might be helpful for debugging purposes.

+
+

There are five levels of verbosity:

+ +

First, specify the log file, human-readable timestamps and the verbosity level in the server part of +/etc/unbound/unbound.conf.d/pi-hole.conf:

+
server:
+    # If no logfile is specified, syslog is used
+    logfile: "/var/log/unbound/unbound.log"
+    log-time-ascii: yes
+    verbosity: 1
+
+

Second, create log dir and file, set permissions:

+
sudo mkdir -p /var/log/unbound
+sudo touch /var/log/unbound/unbound.log
+sudo chown unbound /var/log/unbound/unbound.log
+
+

On modern Debian/Ubuntu-based Linux systems, you'll also have to add an AppArmor exception for this new file so unbound can write into it.

+

Create (or edit if existing) the file /etc/apparmor.d/local/usr.sbin.unbound and append

+
/var/log/unbound/unbound.log rw,
+
+

to the end (make sure this value is the same as above). Then reload AppArmor using

+
sudo apparmor_parser -r /etc/apparmor.d/usr.sbin.unbound
+sudo service apparmor restart
+
+

Lastly, restart unbound:

+
sudo service unbound restart
+
+

Verifying that Pi-hole is querying unbound as its upstream

+

Query a dns using dig:

+
dig en.wikipedia.org @127.0.0.1
+
+

Then view Pi-hole's log file, follow a query seeing it sent to and receiving a reply from 127.0.0.1#5335 such as below:

+
sudo tail /var/log/pihole/pihole.log
+
+Nov 24 11:57:47 dnsmasq[973]: query[A] en.wikipedia.org from 127.0.0.1
+Nov 24 11:57:47 dnsmasq[973]: forwarded en.wikipedia.org to 127.0.0.1#5335
+Nov 24 11:57:47 dnsmasq[973]: reply en.wikipedia.org is <CNAME>
+Nov 24 11:57:47 dnsmasq[973]: reply dyna.wikimedia.org is 103.102.166.224
+
+

If you see the reply to queries from 127.0.0.1#5335, then Pi-hole is using unbound as its upstream.

+

Common Issues & Troubleshooting

+

Fix so-rcvbuf warning in unbound

+

The configuration in /etc/unbound/unbound.conf.d/pi-hole.conf sets the socket receive buffer size for incoming DNS queries to a higher-than-default value in order to handle high query rates:

+
so-rcvbuf: 1m
+
+

As a result, you may see this warning in unbound logs:

+
so-rcvbuf 1048576 was not granted. Got 425984. To fix: start with root permissions(linux) or sysctl bigger net.core.rmem_max(linux) or kern.ipc.maxsockbuf(bsd) values.
+
+

To fix it:

+
    +
  1. +

    Check the current limit. This will show something like net.core.rmem_max = 425984:

    +
    sudo sysctl net.core.rmem_max
+
    +
    2. +
  2. +

    Temporarily increase the limit to match unbound's request:

    +
    sudo sysctl -w net.core.rmem_max=1048576
+
    +
    3. +
  3. +

    Make it permanent. Edit /etc/sysctl.d/99-unbound.conf (or on old systems eg Debian ≤ 12 edit /etc/sysctl.conf) and add or edit the line:

    +
    net.core.rmem_max=1048576
+
    +
    4. +
  4. +

    Save and apply:

    +

    On up to date systems (eg Debian 13)

    +
    sudo systemctl restart systemd-sysctl
+
    +

    Older systems (eg Debian ≤ 12)

    +
    sudo sysctl -p
+
    +
    5. +
  5. +

    Restart unbound:

    +
    sudo service unbound restart
+
    +
    6. +
+

Uninstall unbound

+

To remove unbound from your system run

+
sudo apt remove unbound
+
+

Make sure to switch to another upstream DNS server for Pi-hole.

+ + +