Adding instructions for adding Pi-hole to a Unifi USG's DHCP stack.

Co-authored-by: yubiuser <ckoenig@posteo.de>

Signed-off-by: John Fox <classicyuppie@mac.com>

docs/routers/ubiquiti-usg.md

@@ -0,0 +1,64 @@
+This guide was developed using a Ubiquiti Cloud Key v2 with UniFi Network v7.1.61. Following the first method below will have you adding your Pi-hole as a DNS server for all devices on your LAN. Following the second method below will have DNS queries route through your USG and then to your Pi-hole. Either option is valid, depending on your specific requirements, but it is recommended to choose one or the other - not both.
+
+> Note:
+While this guide attempts to cover both IPv4 and IPv6, your mileage may vary.
+
+### Grab your IPv4 and IPv6 address from your Raspi
+
+SSH into your Raspi. A quick `ifconfig eth0` (substituting `eth0` for the applicable network interface) will get you the address information:
+
+```
+eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
+        inet 192.168.0.9  netmask 255.255.255.0  broadcast 192.168.0.255
+        inet6 2001:470:5:3::8ed  prefixlen 128  scopeid 0x0<global>
+        inet6 2001:470:5:3:8d70:e92e:7030:6eef  prefixlen 64  scopeid 0x0<global>
+        inet6 fe80::337f:710d:6781:4c85  prefixlen 64  scopeid 0x20<link>
+        ether dc:a6:32:0e:31:2d  txqueuelen 1000  (Ethernet)
+        RX packets 1297459  bytes 1279521260 (1.1 GiB)
+        RX errors 0  dropped 0  overruns 0  frame 0
+        TX packets 2315988  bytes 2766370095 (2.5 GiB)
+        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
+```
+
+Take note of the `inet` address, and the `inet6` address which starts with `fe` (denotes a local link or LAN address). Those are the IPs which you'll use as your DNS servers in the USG. For this example, we'll be using the `192.168.0.9` and `fe80::337f:710d:6781:4c85` IPs for the following directions.
+
+### Method 1: Distribute Pi-hole as DNS server via DHCP
+
+Choosing this option will have DNS queries taking the following path:
+
+```
+(Clients) -> Pi-hole -> Upstream DNS Server
+```
+
+Go to **Settings** --> **Networks** and click on the Network line that you want to modify:
+
+![Screenshot of USG LAN](../images/usg-lan.png)
+
+Under **DHCP**, in the DHCP Server Management section click "Show options" to reveal the **DHCP DNS Server** section. Check the **Enable** box and enter your Raspi's IPv4 address here.
+
+![Screenshot of USG LAN DHCP settings](../images/usg-lan-dhcp.png)
+
+Scroll down to **IPv6**, and under the **DHCPv6/RDNSS DNS Control** section, uncheck **Auto** if it's enabled and enter Raspi's IPv6 address here. Click **Apply Changes** to have the settings persistently saved.
+
+![Screenshot of USG LAN DHCPv6 settings](../images/usg-lan-dhcpv6.png)
+
+All client devices on your network should now automatically be configured with a single IPv4 and single IPv6 address for DNS resolution. If you don't see your client devices update quickly enough, you *can* toggle Wi-Fi off/on or disconnect the Ethernet cable for a couple of seconds and then reconnect it.
+
+### Method 2: Using your Pi-hole as a resolve for your USG
+
+If you'd rather have your USG forward all DNS traffic to Pi-hole, you can complete this *alternative* step. Doing so will have DNS queries taking the following path:
+
+```
+(Clients) -> USG -> Pi-hole -> Upstream DNS Server
+```
+
+!!! warning
+    Keep in mind that if you are using your USG's IP address as an upstream resolver for your Pi-hole together with this configureation, ***this will cause a resolver loop***. Make sure to have another upstream DNS server(s) set in your Pi-hole's configuration, or use Pi-hole as [your own recursive DNS server with Unbound](https://docs.pi-hole.net/guides/dns/unbound/?h=unbound#configure-unbound).
+
+Log into your Unifi Cloud Key. Go to **Settings** -> **Internet**. Click on the WAN line that appears.
+
+![Screenshot of USG WAN](../images/usg-wan.png)
+
+Under **Advanced**, in the DNS Server section uncheck the Auto box and add your Raspi's IPv4 address. This allows your USG to use Pi-hole for all DNS lookups. Click **Apply Changes** to have the settings persistently saved.
+
+![Screenshot of USG WAN Advanced settings](../images/usg-wan-advanced.png)

mkdocs.yml

@@ -177,9 +177,10 @@ nav:
       - 'Caddy': guides/webserver/caddy.md
       - 'Traefik (not in Docker)': guides/webserver/traefik-nodocker.md
   - 'Router setup':
+    - 'ASUS router': routers/asus.md
     - 'Fritz!Box (EN)': routers/fritzbox.md
     - 'Fritz!Box (DE)': routers/fritzbox-de.md
-    - 'ASUS router': routers/asus.md
+    - 'Ubiquiti USG': routers/ubiquiti-usg.md
   - 'FAQ': main/faq.md
   - 'Community Projects': main/projects.md