addded initial documentation

docs/features/client-isolation.rst

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+Client Isolation Support
+========================
+
+Normally every client is a wireless network can communicate
+with any other client in the network.
+Client Isolation is a security feature which prevents
+Client-to-Client communication.
+
+There are two different modes to isolate traffic, which can be
+selected by the ``mesh.isolate`` setting in the site or domain
+configuration.
+
+Full Client Isolation Mode
+--------------------------
+
+In the full isolation mode all traffic between wireless and
+wired clients is prevented. The Clients are only able to access
+the Gateway and the Internet.
+
+This mode may not be very useful in a Freifunk context.
+
+It can be activated by setting ``mesh.isolate`` to ``all`` in the
+site or domain configuration.
+
+::
+
+  {
+    mesh = {
+      isolate = 'all'
+    },
+
+    -- more domain specific config follows below
+  }
+
+Wireless Client Isolation Mode
+------------------------------
+
+In the wireless isolation mode only wireless clients are isolated
+from other wireless clients. Communication where a wired client is
+involved is not prevented. So every client can access any wired
+client and every wired client can access all of the clients, only
+wireless clients can not access other wireless clients.
+
+This mode may be more useful in a Freifunk context, but is still
+not as ``frei`` as without any isolation.
+
+It can be activated by setting ``mesh.isolate`` to ``wireless``
+in the site or domain configuration.
+
+::
+
+  {
+    mesh = {
+      isolate = 'wireless'
+    },
+
+    -- more domain specific config follows below
+  }