fix(pihole): added unbound config

Author: rwxd

Applications/PiHole/add-unbound.md

@@ -0,0 +1,146 @@
+# Add Unbound as a recursive DNS Server to the PiHole setup
+
+## Install
+
+```bash
+sudo apt install unbound
+```
+
+## Configuration
+
+Configure unbound with:
+
+- Listen on port 5335
+- TCP & UDP
+- DNSSEC
+- Enable IPv4 & IPv6
+- Ensure privacy of local IP ranges
+
+```yaml
+cat << EOF > /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 yes if you 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
+    # Needs to be commented out if you have a public dns records (e.g. Cloudflare) resolving to
+    # your local IP. Those records will otherwise be unresolvable.
+    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
+EOF
+```
+
+Signal PiHole to use this limit
+
+```python
+cat << EOF > /etc/dnsmasq.d/99-edns.conf
+edns-packet-max=1232
+EOF
+```
+
+### Restart unbound
+
+```bash
+sudo systemctl restart unbound
+```
+
+### Test unbound
+
+#### Query
+
+```bash
+dig google.com @127.0.0.1 -p 5335
+```
+
+#### DNSSec
+
+Get `Servfail`
+
+```bash
+dig sigfail.verteiltesysteme.net @127.0.0.1 -p 5335
+```
+
+Get `NOERROR`
+
+```bash
+dig sigok.verteiltesysteme.net @127.0.0.1 -p 5335
+```
+
+### Configure PiHole
+
+Now we need to tell PiHole to use unbound as an upstream DNS server.
+
+This is done by editing `/etc/pihole/setupVars.conf` and adding/replacing the following line:
+
+```bash
+PIHOLE_DNS_1=127.0.0.1#5335
+PIHOLE_DNS_2=127.0.0.1#5335
+```
+
+Restart PiHole
+
+```bash
+systemctl restart pihole-FTL.service
+```
+
+The PiHole web interface should now show under `//admin/settings.php?tab=dns` that the upstream DNS server is `127.0.0.1#5335`.
+