add ufw doc

docs/sources/installation/ubuntulinux.rst

@@ -19,6 +19,8 @@ Docker has the following dependencies
 * Linux kernel 3.8 (read more about :ref:`kernel`)
 * AUFS file system support (we are working on BTRFS support as an alternative)
 
+Please read :ref:`ufw`, if you plan to use `UFW (Uncomplicated Firewall) <https://help.ubuntu.com/community/UFW>`_
+
 .. _ubuntu_precise:
 
 Ubuntu Precise 12.04 (LTS) (64-bit)
@@ -135,3 +137,35 @@ Verify it worked
 
 
 **Done!**, now continue with the :ref:`hello_world` example.
+
+
+.. _ufw:
+
+Docker and UFW
+^^^^^^^^^^^^^^
+
+Docker uses a bridge to manage containers networking, by default UFW drop all `forwarding`, a first step is to enable forwarding:
+
+.. code-block:: bash
+
+   sudo nano /etc/default/ufw
+   ----
+   # Change:
+   # DEFAULT_FORWARD_POLICY="DROP"
+   # to
+   DEFAULT_FORWARD_POLICY="ACCEPT"
+
+Then reload UFW:
+
+.. code-block:: bash
+
+   sudo ufw reload
+
+
+UFW's default set of rules denied all `incoming`, so if you want to be able to reach your containers from another host,
+you should allow incoming connexions on the docker port (default 4243):
+
+.. code-block:: bash
+
+   sudo ufw allow 4243/tcp
+