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       ufw-framework - using the ufw framework


       ufw provides both a command line interface and a framework for managing
       a netfilter firewall. While the ufw command provides  an  easy  to  use
       interface  for  managing  a  firewall,  the  ufw framework provides the
       administrator methods to customize default behavior and add  rules  not
       supported  by  the  command  line  tool. In this way, ufw can take full
       advantage of Linux netfilter's power and flexibility.


       The framework provides boot time initialization, rules files for adding
       custom  rules, a method for loading netfilter modules, configuration of
       kernel parameters and configuration of IPv6. The framework consists  of
       the following files:

              initialization script

              rules file containing rules evaluated before UI added rules

              rules  file  containing  UI  added  rules  (managed with the ufw

              rules file containing rules evaluated after UI added rules

              high level configuration

              kernel network tunables

              additional high level configuration


       ufw is started  on  boot  with  /lib/ufw/ufw-init.  This  script  is  a
       standard  SysV  style initscript used by the ufw command and should not
       be modified. It supports the following arguments:

       start: loads the firewall

       stop:  unloads the firewall

              reloads the firewall

              same as restart

              basic status of the firewall

              same as stop, except does not check if the firewall  is  already

              flushes the built-in chains, deletes all non-built-in chains and
              resets the policy to ACCEPT

       ufw uses many user-defined chains in addition to the built-in  iptables
       chains.  If  MANAGE_BUILTINS  in  /etc/defaults/ufw is set to 'yes', on
       stop and reload the built-in chains are flushed. If it is set to  'no',
       on  stop  and  reload  the ufw secondary chains are removed and the ufw
       primary chains are flushed. In addition to flushing  the  ufw  specific
       chains,  it  keeps the primary chains in the same order with respect to
       any other user-defined chains that may have been added. This allows for
       ufw  to  interoperate  with  other  software  that may manage their own
       firewall rules.

       To ensure your firewall is loading on boot,  you  must  integrate  this
       script into the boot process. Consult your distribution's documentation
       for the proper way to modify your boot process if ufw  is  not  already


       ufw  is  in part a front-end for iptables-restore, with its rules saved
       in /etc/ufw/before.rules, /etc/ufw/after.rules and /lib/ufw/user.rules.
       Administrators  can  customize  before.rules and after.rules as desired
       using the standard iptables-restore syntax.   Rules  are  evaluated  as
       follows:  before.rules  first,  user.rules  next, and after.rules last.
       IPv6 rules are evaluated in the same way, with the  rules  files  named
       before6.rules,  user6.rules  and  after6.rules.  Please  note  that ufw
       status only shows rules added with ufw and not the rules found  in  the
       /etc/ufw rules files.

       Important:  ufw only uses the *filter table by default. You may add any
       other tables such as *nat, *raw and *mangle as desired. For each  table
       a corresponding COMMIT statement is required.

       After  modifying  any of these files, you must reload ufw for the rules
       to take effect.  See the EXAMPLES section  for  common  uses  of  these
       rules files.


       Netfilter has many different connection tracking modules. These modules
       are aware of the underlying protocol and  allow  the  administrator  to
       simplify  his  or her rule sets. You can adjust which netfilter modules
       to load by adjusting IPT_MODULES  in  /etc/defaults/ufw.  Some  popular
       modules to load are:



       ufw  will  read  in  /etc/ufw/sysctl.conf on boot when enabled.  Please
       note  that  /etc/ufw/sysctl.conf  overrides  values   in   the   system
       systcl.conf  (usually  /etc/sysctl.conf). Administrators can change the
       file used by modifying /etc/default/ufw.


       IPv6 is disabled by default and all  incoming,  outging  and  forwarded
       packets  are  dropped,  with  the  exception of traffic on the loopback
       interface.  To  change  this   behavior,   set   IPV6   to   'yes'   in
       /etc/defaults/ufw. See the ufw manual page for details.


       As  mentioned,  ufw  loads its rules files into the kernel by using the
       iptables-restore and ip6tables-restore commands. Users wanting  to  add
       rules  to  the  ufw rules files manually must be familiar with these as
       well as the iptables and ip6tables  commands.  Below  are  some  common
       examples  of  using the ufw rules files.  All examples assume IPv4 only
       and that DEFAULT_FORWARD_POLICY in /etc/defaults/ufw is set to DROP.

   IP Masquerading
       To allow IP masquerading for computers from the  network  to
       share the single IP address on eth0:

       Edit /etc/ufw/sysctl.conf to have:

       Add to the end of /etc/ufw/before.rules, after the *filter section:
               :POSTROUTING ACCEPT [0:0]
               -A POSTROUTING -s -o eth0 -j MASQUERADE

       If  your  firewall is using IPv6 tunnels or 6to4 and is also doing NAT,
       then you should not usually masquerade protocol  '41'  (ipv6)  packets.
       For  example,  instead  of  the  above,  /etc/ufw/before.rules  can  be
       adjusted to have:
               :POSTROUTING ACCEPT [0:0]
               -A  POSTROUTING  -s  --protocol  !  41  -o  eth0 -j

   Port Redirections
       To forward tcp port 80 on eth0 to go to the webserver at

       Edit /etc/ufw/sysctl.conf to have:

       Add to the *filter section of /etc/ufw/before.rules:
               -A ufw-before-forward -m state --state RELATED,ESTABLISHED \
                 -j ACCEPT
               -A ufw-before-forward -m state --state NEW -i eth0 \
                 -d -p tcp --dport 80 -j ACCEPT

       Add to the end of /etc/ufw/before.rules, after the *filter section:
               :PREROUTING ACCEPT [0:0]
               -A PREROUTING -p tcp -i eth0 --dport 80 -j DNAT \

   Egress filtering
       To block RFC1918 addresses going out of eth0:

       Add in the *filter section of /etc/ufw/before.rules:
               -A ufw-before-forward -o eth0 -d -j REJECT
               -A ufw-before-forward -o eth0 -d -j REJECT
               -A ufw-before-forward -o eth0 -d -j REJECT

   Full example
       This example combines the other  examples  and  demonstrates  a  simple
       routing firewall. Warning: this setup is only an example to demonstrate
       the functionality of the ufw framework in a concise and  simple  manner
       and  should  not  be used in production without understanding what each
       part does and does not do. Your firewall will undoubtedly  want  to  be
       less open.

       This  router/firewall  has  two  interfaces: eth0 (Internet facing) and
       eth1 (internal LAN). Internal clients have addresses on the
       network  and  should  be  able  to connect to anywhere on the Internet.
       Connections to port 80 from the Internet should be forward to
       Access  to ssh port 22 from the administrative workstation (
       to this machine should be allowed. Also make sure no  internal  traffic
       goes to the Internet.

       Edit /etc/ufw/sysctl.conf to have:

       Add to the *filter section of /etc/ufw/before.rules:
               -A ufw-before-forward -m state --state RELATED,ESTABLISHED \
                 -j ACCEPT

               -A ufw-before-forward -i eth1 -s -o eth0 -m state \
                 --state NEW -j ACCEPT

               -A ufw-before-forward -m state --state NEW -i eth0 \
                 -d -p tcp --dport 80 -j ACCEPT

               -A ufw-before-forward -o eth0 -d -j REJECT
               -A ufw-before-forward -o eth0 -d -j REJECT
               -A ufw-before-forward -o eth0 -d -j REJECT

       Add to the end of /etc/ufw/before.rules, after the *filter section:
               :PREROUTING ACCEPT [0:0]
               :POSTROUTING ACCEPT [0:0]
               -A PREROUTING -p tcp -i eth0 --dport 80 -j DNAT \
               -A POSTROUTING -s -o eth0 -j MASQUERADE

       For allowing ssh on eth1 from, use the ufw command:
               # ufw allow in on eth1 from to any port 22 proto tcp


       ufw,       iptables(8),       ip6tables(8),        iptables-restore(8),
       ip6tables-restore(8), sysctl(8), sysctl.conf(5)


       ufw is Copyright 2008-2009, Canonical Ltd.

       ufw  and  this  manual  page was originally written by Jamie Strandboge