Add router page for OPNsense

docs/routers/opnsense.md

@@ -0,0 +1,26 @@
+This guide was developed using OPNsense 23.7.12, but should work for others too.
+
+!!! note There is no single way to do it right. Choose the one best fitting your needs.
+
+### Using PiHole as a global DNS server
+
+This sets up PiHole as your global DNS server. Unless manually configured otherwise, all devices on your network will use PiHole as their DNS server.
+
+1. In PiHole, navigate to `Settings -> DNS` and ensure you have at least one external upstream DNS server enabled.
+
+   **Do not use your OPNsense IP address as this will cause a circular dependency.**
+
+2. In OPNsense navigate to `Settings -> General -> Networking`.
+3. Under DNS Servers, enter the IPv4 address of your PiHole server, and set the gateway to your WAN interface.
+4. Uncheck `Allow DNS server list to the overridden by DHCP/PPP on WAN`.
+5. Click Save.
+
+### Using PiHole as a DNS server for a single interface
+
+You can set up custom DNS servers to use per local interface. For instance, you might want to use PiHole on your LAN, but not on your Guest Wifi network.
+
+1. In PiHole, navigate to `Settings -> DNS`. You should either have at least one external DNS server configured, or have your OPNsense IP address set as an external DNS server.
+2. In OPNsense, navigate to `Services -> DHCPv4 -> [<YOUR INTERFACE>]`
+3. Under DNS servers, remove any other IP addresses and add your PiHole server's IP address to the list.
+4. Click Save
+5. You will also need to ensure that clients connected to that interface can communicate with PiHole by adding a relevant firewall entry.

mkdocs.yml

@@ -192,6 +192,7 @@ nav:
     - 'Fritz!Box (EN)': routers/fritzbox.md
     - 'Fritz!Box (DE)': routers/fritzbox-de.md
     - 'Nokia G-240W-B': routers/nokia-G240WB.md
+    - 'OPNsense': routers/opnsense.md
     - 'TP-Link': routers/tp-link.md
     - 'Ubiquiti USG': routers/ubiquiti-usg.md
   - 'FAQ': main/faq.md