[3688] Updated the Kea guide that qualifying-suffix is appended to hostname.

This is for host reservations case.

doc/guide/dhcp4-srv.xml

@@ -2129,17 +2129,60 @@ temporarily override a list of interface names and listen on all interfaces.
       it back in the Client FQDN or Hostname option, depending on which of them
       the client has sent to the server. The reserved hostname always takes
       precedence over the hostname supplied by the client or the autogenerated
-      (from the IPv4 address) hostname. If the reservation for the hostname is
-      specified the server ignores the <command>qualifying-suffix</command>
-      parameter and treats the value specified in the reservation as a fully
-      qualified name.</para>
+      (from the IPv4 address) hostname.</para>
 
-      <note>
-        <para>Future Kea versions may provide additional configuration
-        parameters to specify whether the reserved hostname is a fully qualified
-        name or the suffix should be appended.
-        </para>
-      </note>
+      <para>The server qualifies the reserved hostname with the value
+      of the <command>qualifying-suffix</command> parameter. For example, the
+      following subnet configuration:
+<screen>
+    {
+        "subnet4": [ {
+            "subnet": "10.0.0.0/24",
+            "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
+            "reservations": [
+               {
+                 "hw-address": "aa:bb:cc:dd:ee:ff",
+                 "hostname": "alice-laptop"
+               }
+            ]
+         }],
+        "dhcp-ddns": {
+            "enable-updates": true,
+            "qualifying-suffix": "example.isc.org."
+        }
+    }
+</screen>
+      will result in assigning the "alice-laptop.example.isc.org." hostname to the
+      client using the MAC address "aa:bb:cc:dd:ee:ff". If the <command>qualifying-suffix
+      </command> is not specified, the default (empty) value will be used, and
+      in this case the value specified as a <command>hostname</command> will
+      be treated as fully qualified name. Thus, by leaving the
+      <command>qualifying-suffix</command> empty it is possible to qualify
+      hostnames for the different clients with different domain names:
+<screen>
+    {
+        "subnet4": [ {
+            "subnet": "10.0.0.0/24",
+            "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
+            "reservations": [
+               {
+                 "hw-address": "aa:bb:cc:dd:ee:ff",
+                 "hostname": "alice-laptop.isc.org."
+               },
+               {
+                 "hw-address": "12:34:56:78:99:AA",
+                 "hostname": "mark-desktop.example.org."
+               }
+
+            ]
+         }],
+        "dhcp-ddns": {
+            "enable-updates": true,
+        }
+    }
+</screen>
+
+      </para>
     </section>
 
     <section id="reservation4-options">