Service: Add Dynamic DNS chapter

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diff --git a/docs/ch11-services.rst b/docs/ch11-services.rst
index 2812a31a..43397d38 100644
--- a/docs/ch11-services.rst
+++ b/docs/ch11-services.rst
@@ -640,3 +640,154 @@ servers:
   set service dns forwarding name-server 2001:4860:4860::8844
   set service dns forwarding listen-on 'eth1'
 
+Dynamic DNS
+-----------
+
+VyOS is able to update a remote DNS record when an interface gets a new IP
+address. In order to do so, VyOS includes ddclient_, a perl script written for
+this exact purpose.
+
+ddclient_ uses two methods to update a DNS record. The first one will send
+updates directly to the DNS daemon, in compliance with RFC2136_. The second
+one involves a third party service, like DynDNS.com or any other similar
+website. This method uses HTTP requests to transmit the new IP address. You
+can configure both in VyOS.
+
+VyOS CLI and RFC2136
+^^^^^^^^^^^^^^^^^^^^
+
+First, create an RFC2136_ config node :
+
+.. code-block:: sh
+
+  edit service dns dynamic interface eth0 rfc2136 <confignodename>
+
+Present your RNDC key to ddclient :
+
+.. code-block:: sh
+
+  set key /config/dyndns/mydnsserver.rndc.key
+
+Set the DNS server IP/FQDN :
+
+.. code-block:: sh
+
+  set server dns.mydomain.com
+
+Set the NS zone to be updated :
+
+.. code-block:: sh
+
+  set zone mydomain.com
+
+Set the records to be updated :
+
+.. code-block:: sh
+
+  set record dyn
+  set record dyn2
+
+You can optionally set a TTL (note : default value is 600 seconds) :
+
+.. code-block:: sh
+
+  set ttl 600
+
+This will generate the following ddclient config blocks:
+
+.. code-block:: sh
+
+  server=dns.mydomain.com
+  protocol=nsupdate
+  password=/config/dyndns/mydnsserver.rndc.key
+  ttl=600
+  zone=mydomain.com 
+  dyn
+  server=dns.mydomain.com
+  protocol=nsupdate
+  password=/config/dyndns/mydnsserver.rndc.key
+  ttl=600
+  zone=mydomain.com
+  dyn2
+
+You can also keep a different dns zone updated. Just create a new config node:
+
+.. code-block:: sh
+
+  edit service dns dynamic interface eth0 rfc2136 <confignode2>
+
+VyOS CLI and HTTP dynamic DNS services
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+VyOS is also able to use any service relying on protocols supported by ddclient.
+
+To use such a service, you must define a login, a password, one or multiple
+hostnames, a protocol and a server.
+
+.. code-block:: sh
+
+  edit service dns dynamic interface eth0 service HeNet
+  set login my-login # set password my-password
+  set host-name my-tunnel-id
+  set protocol dyndns2
+  set server ipv4.tunnelbroker.net
+
+VyOS is also shipped with a list of known services. You don't need to set the
+protocol and server value as VyOS has defaults provided for those. These are
+the services VyOS knows about:
+
+* afraid
+* changeip
+* dnspark
+* dslreports
+* dyndns
+* easydns
+* namecheap
+* noip
+* zoneedit
+
+To use DynDNS for example:
+
+.. code-block:: sh
+
+  edit service dns dynamic interface eth0 service dyndns
+  set login my-login
+  set password my-password
+  set host-name my-dyndns-hostname
+
+It's possible to use multiple services :
+
+.. code-block:: sh
+
+  edit service dns dynamic interface eth0 service dyndns
+  set login my-login
+  set password my-password
+  set host-name my-dyndns-hostname
+  edit service dns dynamic interface eth0 service HeNet
+  set login my-login
+  set password my-password
+  set host-name my-tunnel-id
+  set protocol dyndns2
+  set server ipv4.tunnelbroker.net
+
+ddclient behind NAT
+^^^^^^^^^^^^^^^^^^^
+
+By default, ddclient will update a dynamic dns record using the IP address
+directly attached to the interface. If your VyOS instance is behind NAT, your
+record will be updated to point to your internal IP.
+
+ddclient_ has another way to determine the WAN IP address. This is controlled
+by these two options:
+
+.. code-block:: sh
+
+  set service dns dynamic interface eth0 use-web url
+  set service dns dynamic interface eth0 use-web skip
+
+ddclient_ will load the webpage at `[url]` and will try to extract an IP
+address for the response. ddclient_ will skip any address located before the
+string set in `[skip]`.
+
+.. _ddclient: http://sourceforge.net/p/ddclient/wiki/Home/
+.. _RFC2136: https://www.ietf.org/rfc/rfc2136.txt