+ Recursive DNS server

Configuration.md

@@ -5,6 +5,7 @@ Most of these settings can be changed via the web-based admin interface. However
 * [Command-line arguments](#command-line)
 * [Configuring upstreams](#upstreams)
   * [Specifying upstreams for domains](#upstreams-for-domains)
+  * [Recursive DNS server](Unbound.md)
 * [Configuring clients friendly names](#friendly-names)
 * [Configuration file](#configuration-file)
 

Unbound.md

@@ -0,0 +1,23 @@
+# Recursive DNS server
+
+A recursive DNS server doesn't require an upstream server to resolve a domain name (e.g. `www.hostname.com`).  Instead, it starts with Root DNS servers and then recursively asks authoritative DNS servers for each part of the domain name (e.g. `com`, then `hostname.com`).  Finally, it reaches the specific authoritative server which is responsible for the target domain name (e.g. `www.hostname.com`).  One such recursive DNS server is `unbound`.  You can read more information about it here: https://nlnetlabs.nl/projects/unbound/about/.
+
+AdGuard Home can work with `unbound` on several system configurations (currently, Linux-amd64 and Linux-arm).
+
+
+## Enable recursive DNS server
+
+To enable recursive DNS server, add `unbound` to the "Upstream DNS servers" list in UI.
+If you want to use it for specific domains only, use `[/hostname/]unbound` setting.
+
+
+## Configure libunbound
+
+libunbound has many configuration settings that you can set in `AdGuardHome.yaml` file.  The list of supported settings is located here: https://nlnetlabs.nl/documentation/unbound/unbound.conf/
+
+For example, to set libunbound cache size equal to 8 megabytes, use this setting:
+
+	dns:
+	...
+	  unbound_settings:
+	  - 'msg-cache-size: 8m'