UFW
---
https://wiki.ubuntu.com/UbuntuFirewall


What's in a name?
-----------------
What does it mean?  I like 'Uncomplicated Firewall', but really, it's up to
you. :)  If you like it, you might pick 'Universal Firewall', 'Ultimate
Firewall', or considering its current state, 'Unfinished Firewall'. If you are
not a fan, perhaps 'Unbearable Firewall'.


Install
-------
Users can install with:
# python ./setup.py install
$ python ./setup.py install --home=PREFIX


Distributions which install to a build directory for packaging can install
with:
$ python ./setup.py install --root=PREFIX

Eg:
python ./setup.py install --root=/tmp/ufw


Basic Layout
------------
/usr/sbin/ufw 			is the UI for people (have different backends)
/etc/defaults/ufw 		high level configuration
/etc/ufw/before[6].rules 	rules evaluated before UI added rules
/etc/ufw/after[6].rules 	rules evaluated after UI added rules
/var/lib/ufw/user[6].rules	UI added rules (not to be modified)
/etc/ufw/sysctl.conf 		kernel network tunables
/etc/init.d/ufw			start script


Usage
-----
ufw enable|disable 		turn firewall on and off (including at boot)
ufw default allow|deny		updates default policy
ufw logging on|off		updates backend logging (*.rules)
ufw status			displays firewall status (user.rules only)
ufw allow|deny|limit RULE	add RULE to firewall

See 'man ufw' and also Ubuntu's tutorial at:
http://doc.ubuntu.com/ubuntu/serverguide/C/firewall.html


Chains
------
ufw uses several chains to allow ease of use and flexibility. The chains are
organized as follows:

INPUT -> ufw-before-input -> ufw-user-input -> ufw-after-input
OUTPUT -> ufw-before-output -> ufw-user-output -> ufw-after-output
FORWARD -> ufw-before-forward -> ufw-user-forward -> ufw-after-forward

The 'before' chains are setup in 'before.rules', the 'after' chains in
'after.rules' and the 'user' chains are maintained by ufw. If an administrator
wants to add rules manually, the rules should be added to 'before.rules' and
'after.rules'.

There is some default configuration in both 'before.rules' and 'after.rules',
and this configuration is not displayed with 'ufw status' (but can always
be viewed with 'iptables -L -n' or 'iptables -L [chain] -n'. See the iptables
man page for details.


Advanced Configuration
----------------------
ufw can be thought of two parts, the ufw command-line program and the ufw
framework. The ufw command is intentially kept as simple as possible, so users
can do common tasks more easily. The framework (ie the bootscripts, setup of
the chains (see above), sysctl configuration, etc) is very flexible, and since
ufw is simply a frontend for iptables, anything that can be done with iptables
can be done within the ufw framework.

As an example, to perform port redirection, users can add to the top of
/etc/ufw/before.rules, before the '*filter' section:
*nat
:PREROUTING ACCEPT [0:0]
# redirect all incoming requests to tcp port 80 to tcp port 22
-A PREROUTING -p tcp --dport 80 -j REDIRECT --to-port 22
COMMIT

then run:
# ufw disable
# ufw enable
# ufw allow 80/tcp	(required only if ufw blocks requests to this port)


To add NAT masquerading to the above, change the nat table that was just added
to something like:
*nat
:PREROUTING ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
-A PREROUTING -p tcp --dport 80 -j REDIRECT --to-port 22
# Forward traffic from eth1 through eth0.
-A POSTROUTING -s 192.168.0.0/24 -o eth0 -j MASQUERADE
COMMIT

then adjust /etc/default/ufw to have:
DEFAULT_FORWARD_POLICY="ACCEPT"

and /etc/ufw/sysctl.conf to have:
net.ipv4.ip_forward=1

then run:
# ufw disable
# ufw enable


It's important to remember that ufw will only flush the chains and tables it
manages, so if if you need to flush the nat table to restart anew, please do:
# iptables -F -t nat

Similarly, to see what rules are in the nat table's chains, use:
# iptables -L -n -t nat

See 'man iptables' for details.


Remote Management
-----------------
On /etc/init.d/ufw start and 'ufw enable' the chains are flushed, so ssh may
drop. This is needed so ufw is in a consistent state. Once the ufw is 'enabled'
it will insert rules into the existing chains, and therefore not flush the
chains (but will when modifying a rule or changing the default policy).

You can insert rules before enabling the firewall however, so it is often
a good idea to to:
$ sudo ufw allow proto tcp from any to any port 22
$ sudo ufw enable

In this case, the chains are still flushed, but the ssh port will be open
after enabling the firewall.


IPV6
----
ufw has support for IPv6, but it is disabled by default.  To enable, modify
/etc/default/ufw (or wherever this is installed) to have:

IPV6=yes

Then do:
# ufw disable
# ufw enable


Application Integration
-----------------------
ufw has support for application integration. This allows for administrators
and developers to put profiles in /etc/ufw/applications.d and have users use
these profiles in their rules. Profiles use the .INI syntax, and examples
can be found in the examples/ directory. See 'man ufw' for details.


Upgrading
---------
If upgrading from 0.17 or below to 0.18, new chains to support the 'limit'
command will be added automatically.


Testing
-------
$ mkdir -p /tmp/ufw/usr /tmp/ufw/etc
$ python ./setup.py install --home=/tmp/ufw

The edit /tmp/ufw/lib/python/ufw/backend.py to have (since it's installed in
/tmp):
        self.do_checks = False

Now do:
$ /tmp/ufw/usr/sbin/ufw help

Here is a command to do it all at once:
$ rm -rf /tmp/ufw && mkdir -p /tmp/ufw/usr /tmp/ufw/etc && python ./setup.py install --home=/tmp/ufw && sed -i 's/self.do_checks = True/self.do_checks = False/' /tmp/ufw/lib/python/ufw/backend.py

Then test with:
$ PYTHONPATH=$PYTHONPATH:/tmp/ufw/lib/python /tmp/ufw/usr/sbin/ufw ...

$ sudo sh -c "PYTHONPATH=$PYTHONPATH:/tmp/ufw/lib/python /tmp/ufw/usr/sbin/ufw ..."

Can also just run from the source directory:
$ ./run_tests.sh -s

Or for the root tests (these will modify your existing firewall and insert
kernel modules, so they require root privileges and aren't run by default):
$ sudo ./run_tests.sh -s root



(C) 2008 Canonical Ltd.
