Firewall Builder Frequently Asked Questions

  Vadim Kurland

       vadim@fwbuilder.org
     

   Revision History         
   Revision 0.1             2001-11-25             Revised by: vk             
   Converted to SGML        

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   Table of Contents

   1. Introduction

   2. System requirements, using pre-built packages, compiling from source

   3. Problems, troubleshooting and reporting bugs

   4. Building firewall policy

   5. Installing policy on the firewall

   6. Logging

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                                1. Introduction

   Firewall Builder consists of an object-oriented GUI and a set of policy
   compilers for various firewall platforms. In Firewall Builder, a firewall
   policy is a set of rules; each rule consists of abstract objects that
   represent real network objects and services (hosts, routers, firewalls,
   networks, protocols). Firewall Builder helps users maintain a database of
   objects and allows policy editing using simple drag-and-drop operations.

   Preferences and object databases are stored in XML format. The GUI and
   policy compilers are completely independent. The GUI requires only minimal
   changes in order to add support for a new firewall platform even though a
   new policy compiler must be written. This provides for a consistent
   abstract model and the same GUI for different firewall platforms.
   Standardized XML data format opens possibility for many user interfaces
   and policy compiler implementations, all interchangeable.

   We ship a policy compiler for the popular free firewall iptables
   http://netfilter.filewatcher.org/ and are currently working on support for
   ip_filter http://coombs.anu.edu.au/~avalon/. Because of the modular
   architecture, Firewall Builder can be used to manage firewalls built on a
   variety of platforms including, but not limited to, Linux using iptables
   or ipfilter on FreeBSD or Solaris.

   The GUI is written using GTK--. We distribute binary RPM packages for
   RedHat 7.1 / 7.2 and Mandrake 8.1. Binary packages for Debian can be
   downloaded from our "contrib" area.

   An interactive "Druid" facilitates an easy kick-start. Basically, to
   start, one should create objects for the firewall and internal network and
   then use the druid. It will ask a few questions and then build a basic
   skeleton policy, which can be edited manually. The same druid can be used
   to add specific "standard" rules later on.

   We provide a mechanism for automated creation of network objects using
   information either from the /etc/hosts file or by importing DNS zones.

   Solutions to many typical problems and answers to many questions can also
   be found in Firewall Builder Tutorial. Many cases people deal with while
   configuring their firewalls are covered in the Tutorial in great details.
   Some topics can be found both in Tutorial and FAQ, but since FAQ is
   intended just as brief reference document, it provides only short answer
   to the question and refers reader to Tutorial for more detailed
   explanation. Firewall Builder Tutorial can be found online:
   http://www.fwbuilder.org/pages/Tutorial/index.html

     ----------------------------------------------------------------------

    2. System requirements, using pre-built packages, compiling from source

   2.1. What are the system requirements for Firewall Builder ?

   2.2. Where do I get GTK-- packages for RedHat 7.0 and 7.1 ?

   2.3. I want to use pre-built binary package. What do I need to download
   and install?

   2.4. Does Firewall Builder need GNOME?

   2.5. I am trying to compile Firewall Builder v0.9.6 from source, but
   configure complains "libfwbuilder not installed"

   2.6. What firewall platforms are supported ?

   2.1. What are the system requirements for Firewall Builder ?

   These are listed in the file "Requirements" in the docs directory. It is
   /usr/share/doc/fwbuilder/Requirements or online:
   http://www.fwbuilder.org/pages/Requirements.html

   2.2. Where do I get GTK-- packages for RedHat 7.0 and 7.1 ?

   See gtk-- home page at http://gtkmm.sourceforge.net/ and follow link
   "Download" or directly in http://www.hvrlab.org/pub/gtkmm/

   2.3. I want to use pre-built binary package. What do I need to download
   and install?

   We distribute pre-built binary packages for some Linux distributions. You
   would need to download and install the following (actual names of the
   packages vary depending on the naming convention for given distribution):

     * The API: libfwbuilder

     * GUI: fwbuilder

     * Policy compiler for iptables: fwbuilder-iptables

   As policy compilers for other firewall platforms become available, they
   will appear in the download area.

   You may also want to check what is available under "Contrib" in the
   download area. There are useful install, boot-time startup and other
   scripts contributed by users and beta-testers. Pre-built binary packages
   for Debian and SuSe are also available in "Contrib" area.

   2.4. Does Firewall Builder need GNOME?

   As of version 0.9.7 Firewall Builder does not need GNOME anymore. All
   widgets which are part of libgnomeui library have been rewritten so
   Firewall Builder now uses only gtk+ and gtk-- libraries. This should
   simplify porting to other OS and should make it possibly to use Firewall
   Builder on Linux systems using KDE.

   2.5. I am trying to compile Firewall Builder v0.9.6 from source, but
   configure complains "libfwbuilder not installed"

   As of version 0.9.6 the code has been split into three major parts: API,
   GUI and policy compilers. You need to download, compile and install API
   for the rest to compile. The API comes in a separate source archive called
   libfwbuilder-0.10.0.tar.gz. Compile and install it as usual, using
   "./configure; make; make install" procedure.

   2.6. What firewall platforms are supported ?

   As of version 0.9.3 we support iptables and are working on ipfilter policy
   compiler. We dropped support for ipchains as obsolete technology and
   because lack of time

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                3. Problems, troubleshooting and reporting bugs

   3.1. fwbuilder binary does not start 1

   3.2. fwbuilder binary does not start 2

   3.3. fwbuilder or one of policy compilers crashes. What to do ?

   3.4. I get "I/O Error" while compiling policy. There is no other
   indication of error though.

   3.5. fwbuilder crashes on my Debian or Mandrake or SuSe system. What do I
   do ?

   3.1. fwbuilder binary does not start 1

   If you get this error:

   fwbuilder: error while loading shared libriaries: libfwbuilder.so.0:
   cannot load shared object file: no such file or directory.

   Then the GUI binary (fwbuilder) can not find API library libfwbuilder. If
   you are using our pre-built binary packages, then make sure you download
   and install package called libfwbuilder. If you compiled from sources,
   then perhaps you installed libfwbuilder with default prefix /usr/local/,
   therefore library went to /usr/local/lib. Dynamic linker ldd can not find
   it there.

   You have the following options:

     * create environment variable LD_LIBRARY_PATH with value /usr/local/lib
       and run fwbuilder from this environment.

     * add /usr/local/lib to the file /etc/ld.so.conf and run ldconfig so it
       will rescan dynamic libraries and add them to its cache.

     * recompile libfwbuilder and fwbuilder with prefix /usr/, this will
       install libfwbuilder.so.0 in /usr/lib. ldd will find it there without
       any changes to environment variables or /etc/ld.so.conf file. To
       change prefix you need to run configure with command line parameter
       "--prefix=/usr". Do this both for libfwbuilder and fwbuilder.

   3.2. fwbuilder binary does not start 2

   If you get this error:

   fwbuilder: error while loading shared libraries: fwbuilder: undefined
   symbol: co nnect__Q23Gtk9ProxyNodePQ23Gtk6ObjectPCcPFv_vPQ24SigC8S
   lotDatab

   Then usually this error happens when old version of libgtkmm or libsigc++
   library is used. Check if you need to upgrade those, you can use our
   Requirements document to find out what versions you need and where can you
   get them from.

   sometimes this error happens even if new rpms have been installed. In this
   case you need to check which library gets picked up by fwbuilder when it
   starts. Sometimes old version gets stuck somewhere on disk after upgrade
   and then ldd loads it instead of newer one. Try to download script called
   "check_libs.sh" from "Contribs" area on Sourceforge site of Firewall
   Builder and then run this script like this:

               check_libs.sh /usr/bin/fwbuilder
            

   it will list all dynamic libraries used by fwbuilder binary and what RPM
   they are part of. Look for libraries which are not part of any installed
   rpm, those are causing of the problem.

   3.3. fwbuilder or one of policy compilers crashes. What to do ?

   Please file a bug on Sourceforge. Provide information we might need to fix
   the problem (in the form of the output of the following commands):

               cat /etc/issue

               rpm -qa | grep gnome
               rpm -qa | grep gtk
               rpm -qa | grep libxml
               rpm -qa | grep libsigc++

               ls -la /usr/share/fwbuilder
               ls -la /usr/share/pixmaps/fwbuilder

               ldd /usr/bin/fwbuilder
               ldd /usr/bin/fwb_ipfilter
               ldd /usr/bin/fwb_iptables
            

   Also send us core file and .xml file with your objects. If program crashes
   but does not generate core file (it shows "crash" dialog instead), run it
   as follows:

               fwbuilder --disable-crash-dialog
            

   It will dump core then.

   3.4. I get "I/O Error" while compiling policy. There is no other
   indication of error though.

   Did you install package with corresponding compiler ? We ship compilers in
   a separate RPMs named like this: fwbuilder-ipchains-0.8.7-2-rh7.i386.rpm

   Check if compiler dumped core. If you can't find it, you may try to run
   compiler manually, providing the following command line parameters:

               $ fwb_iptables  -f path_to_objects.xml   firewall_object_name
            

   All policy compilers have the same command line format.

   3.5. fwbuilder crashes on my Debian or Mandrake or SuSe system. What do I
   do ?

   We can not guarantee that Firewall Builder would work flawlessly on Debian
   or Mandrake or SuSe since we do not have access to these distributions for
   testing.

   Sometimes we recieve packages built for these distributions by volunteers.
   In this case we post these packages in "Contribs" area on the project's
   page on Sourceforge. We do not verify or even try these packages and
   completely rely on people who submit them. We usually post information
   about authors, so if you have questions you can contact them directly.

   We welcome help from anyone who can test Firewall Builder on these
   distributions and provide feedback

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                          4. Building firewall policy

   4.1. Do I need to add rules for "ACK" packets?

   4.2. Druid seems to multiply rules in the policy

   4.3. I use iptables (or other) to protect local host. How do I use
   Firewall Builder to build policy?

   4.4. How can I configure NAT to provide access from the Internet to my
   server behind the firewall ?

   4.5. I see the firewall objects has multiple policies associated with it.
   How do these policies relate to each other and in what order does policy
   compiler scan them to generate firewall code?

   4.1. Do I need to add rules for "ACK" packets?

   Firewall Builder uses "stateful inspection" feature of underlying firewall
   platform. In case of iptables it loads module ip_conntrack which is
   tracking connections opened through the firewall and by the firewall
   itself. Since this module "remembers" each connection, there is no need in
   additional rule for "ACK" or "reply" packets. In fact, this module does
   lot more than keeping track of opened TCP sessions as it does similar
   thing to other protocols as well, where possible. Firewall Builder also
   loads some other modules to keep track of complex protocols, e.g. it loads
   module ip_nat_ftp to support FTP.

   4.2. Druid seems to multiply rules in the policy

   This is how it works now. Interactive Druid does not check for rules in
   existing policy and simply adds new ones. If you run Druid twice and ask
   it to generate the same set of rules, you'll get the same rules many times
   in your policy. This will be improved in subsequent releases.

   4.3. I use iptables (or other) to protect local host. How do I use
   Firewall Builder to build policy?

   Your host may or may not have its IP address assigned dynamically via
   PPPoE or DHCP.

     * 

       If address is static:

          * create firewall object, enter its IP address

          * create interface for it in "Interfaces" tab, mark it as
            "external"

          * add loopback interface named "lo", address 127.0.0.1/255.0.0.0

          * call Druid, chose "Firewall protects local host" and then pick
            rules you want.

       See what Druid have created for you. You can edit and add rules now.

     * 

       If address is dynamic:

          * create firewall object, mark its address as "dynamic"

          * create interface for it in "Interfaces" tab, mark it as
            "external" and "dynamic"

          * add loopback interface named "lo", address 127.0.0.1/255.0.0.0

          * call Druid, chose "Firewall protects local host" and then pick
            rules you want.

   4.4. How can I configure NAT to provide access from the Internet to my
   server behind the firewall ?

   This question is outlined in Firewall Builder Tutorial in great details,
   what follows is just a brief explanation. You can find Tutorial online:
   http://www.fwbuilder.org/pages/Tutorial/index.html

   There are two possibilities here, depending on what IP address you want to
   use to access your server - that of your firewall or virtual one. If you
   use the same address your firewall has, you can arrange access to your
   internal server from outside, and provide your internal users with access
   to the Internet using only one address. This scheme may become a
   limitation though if you have multiple servers inside your network which
   need to be accessed from outside. In the latter case you may want to use
   different port numbers or virtual ip addresses for access to different
   internal servers.

     * 

       Using IP address of the firewall to access your server inside.

       This is easy. Just add rule to the "NAT":

       Table 1.

       +-----------------------------------------------------------+
       |Orig.Src|Orig.Dst|Orig.Srv|Transl.Src|Transl.Dst|Transl.Srv|
       |--------+--------+--------+----------+----------+----------|
       |Any     |Firewall|Any     |Original  |Server    |Original  |
       +-----------------------------------------------------------+

       where "firewall" is the object for your firewall and "Server" is the
       object for your server behind the firewall. This is it, Firewall
       Builder will generate iptables code for DNAT translation using
       firewall's IP address.

     * 

       Using virtual IP address for translation

       Create a rule in "NAT" in a similar way:

       Table 2.

       +-------------------------------------------------------------+
       |Orig.Src|Orig.Dst  |Orig.Srv|Transl.Src|Transl.Dst|Transl.Srv|
       |--------+----------+--------+----------+----------+----------|
       |Any     |Server-NAT|Any     |Original  |Server    |Original  |
       +-------------------------------------------------------------+

       where "Server-NAT" is special object with address of the translation
       you want to create, and "Server" is an object for your server behind
       the firewall.

       In addition to the firewall rule, you need to set up static ARP entry
       and add routing. Asuming external translated address of the server is
       NN.NN.NN.NN, external firewall's interface is eth1 and its internal
       interface is eth0, the following commands would do the trick:

                     # arp -Ds NN.NN.NN.NN eth1 pub 
                     # route add NN.NN.NN.NN dev eth0
                  

       The first command adds static "published" ARP entry, while the second
       command routes it through internal interface

       As of version 0.9.3 iptables compiler can add these two commands to
       the generated firewall script if checkbox "Create ARP entries for DNAT
       translations" is checked in "iptables" tab in firewall object's dialog

   4.5. I see the firewall objects has multiple policies associated with it.
   How do these policies relate to each other and in what order does policy
   compiler scan them to generate firewall code?

   Global Policy rules apply to packets crossing the firewall, regardless of
   the interface they ingress and egress through. In case of iptables this is
   equivalent to the FORWARD chain, although there may be no such direct
   correspondence in other firewall platforms. Even when such correspondence
   does exist, high level Firewall Bulder policy rule may need to be
   converted into multiple rules going into different groups or chains in the
   target platform code beause of number of reasons. To explain this, let's
   consider a situation when Firewall Builder has to generate code for
   iptables firewall and the rule has "Any" as source. Obviously, if source
   is "any", then it should cover any object, including the firewall itself.
   Therefore policy compiler which generates code for iptables places rule
   into both FORWARD and OUTPUT chains. However, both final iptables rules
   won't have interface specified in them since original fwbuilder rule was
   part of the Global Policy which is not associated with any interface.

   Interface Policy rules are associated with certain network interface of
   the firewall. Unlike Global Policy rules, direction can be specified for
   Interface Policy rules. This provides a mechanism for dealing with
   situations where knowing both interface and direction is neccessary, for
   example setting up anti-spoofing rules. Since situations like this are
   rare, we recommend placing most of the firewall rules in the Global Policy
   and only those rules which can not be implemented in any other way into
   Interface Policy.

   At the same time there are target platforms which require that all rules
   are always associated with interfaces. In this case using Global Policy
   rules may not be practical because writing policy compiler capable of
   guessing correct interface may be too complex. One example of such
   platform is Cisco routers, where access lists (ACL) are always associated
   with interfaces.

   When policy compiler generates code for the target platform, it first
   scans NAT rules, then Interface Policies, then Global Policy. This
   determines the order in which lines of the target code are generated.

     ----------------------------------------------------------------------

                      5. Installing policy on the firewall

   5.1. The XML file I save, is it transformed into iptables script and sent
   to the firewall automatically when I click on "Compile"? Or do I have to
   restart something to see the changes applied?

   5.2. I have ipchains installed on my RedHat 7.1 system. How do I switch to
   iptables and start using firewall script generated by Firewall Builder?

   5.1. The XML file I save, is it transformed into iptables script and sent
   to the firewall automatically when I click on "Compile"? Or do I have to
   restart something to see the changes applied?

   "Compile" only calls compiler, which produces a file called after the name
   of the firewall object, with ".fw" extension. This file contains iptables
   sript which needs to be activated. There are two ways to activate it: 1)
   you can simply run it by hand. 2) you can use custom shell script to copy
   this file to where it should be and then run it. If you put this script in
   the "Policy Install Script" field in "Compile/Install" tab of the
   firewall's object dialog, then menu item "Rules/Install" will be
   activated. We have examples of the install script in the "Contrib" area on
   Sourceforge. We do not ship this script with the product because the
   installation and activation procedure is too different on different
   installations. We might standardise on one or another version in the
   future, but for now it is add-on feature and we rely on contributors to
   send us examples of their install scripts. You do not need to reboot your
   firewall to activate the new policy. Iptables script generated by Firewall
   Builder has a code to do a "clean up" job by removing all previous
   iptables settings, before it loads new ones.

   5.2. I have ipchains installed on my RedHat 7.1 system. How do I switch to
   iptables and start using firewall script generated by Firewall Builder?

   You do not need to uninstall ipchains, but you need to deactivate it.

   As root, run the following command:

               # chkconfig --level 2345 ipchains off
            

   if you do not want to reboot at this point, run the following to stop and
   remove ipchains from the memory:

               # /etc/rc.d/init.d/ipchains stop
               # rmmod ipchains
            

   Now simply run iptables script created by fwbuilder to activate your
   firewall.

   RedHat's standard iptables setup depends on their scripts iptables-save
   and iptables-restore. If you wish to stick with RedHat's standard scripts,
   simply run these commands:

               # /etc/rc.d/init.d/iptables save
               # chkconfig --level 2345 iptables on
            

   This will save your configuration to RedHat's standard file
   /etc/sysconfig/iptables in iptables-save format (which is different!) and
   then will restart it every time you reboot your firewall.

   If you do not want to use their scripts, you can use script
   "firewall-install" available in our Contrib area on SourceForge. This
   script comes with a README file which describes its usage.

     ----------------------------------------------------------------------

                                   6. Logging

   6.1. I do not see log records in /var/log/messages, what's wrong?

   6.2. I've got logging working, but I think it sends too much information
   to the log so I can not really find what I am interested in. Is there a
   way to make it more readable?

   6.3. How can I get a list of connections opened through the firewall at
   any given moment of time ?

   6.1. I do not see log records in /var/log/messages, what's wrong?

   RedHat Linux comes with syslog preconfigured to write all log messages
   with level "info" and higher to /var/log/messages, while iptables script
   generated by Firewall Builder by default logs everything as "debug". You
   need either to edit /etc/syslog.conf to make all "debug" messages to be
   logged, or change log level to "info" in iptables tab in firewall dialog

   6.2. I've got logging working, but I think it sends too much information
   to the log so I can not really find what I am interested in. Is there a
   way to make it more readable?

   You can use our script logwatcher.pl available in Contrib area. It reads
   log file /var/log/messages and shows only the following fields from each
   log line:

     * Date and time

     * rule number (assuming you use default setting for the rule prefix
       which looks like this: "RULE %N -- %A")

     * rule action (Deny/Reject/Accept)

     * interface

     * protocol

     * source address and source port

     * destination address and destination port

     * ICMP type and code for ICMP packets

   Note though that this script drops some data logged by iptables to improve
   readability. You may miss some important information because of this, so
   in case of real problem always look in the original log!

   Another, more elaborate version of the same script is logwatcher2.pl. It
   is also available in Contrib area.

   6.3. How can I get a list of connections opened through the firewall at
   any given moment of time ?

   You can use our script connwatcher.pl available in Contrib area. It prints
   the contents of the connections table every second, sort of like top shows
   processes active in the system.