  Ethernet Bridge + netfilter Howto
  Nils Radtke <mailto:Nils.Radtke_@_Think-Future.de>
  v0.8, July 2005

  Setting up an ethernet bridge gives us the chance to integrate a sur-
  veying and/or regulating instance transparently into an existing net-
  work. This setup requires no changes to the logical network topology.
  It is accomplished by plugging the ethernet bridge in the physical
  network topology between the network itself and the routing instance
  (that piece of hardware connected to the Internet).
  ______________________________________________________________________

  Table of Contents


  1. Introduction
  2. Required software
     2.1 Featured Linux kernel
     2.2 Userspace tool: brctl
     2.3 Kernel-Notes

  3. Set Linux up to serve
     3.1 Setting up the bridge
     3.2 Setting up the routing
     3.3 Make it happen again!

  4. Test your new bridged environment!
     4.1 Testing Grounds
     4.2 Ping it, Jim!
     4.3 Actual configuration
        4.3.1 Interface configuration
        4.3.2 Routing configuration
        4.3.3 Iptables configuration
     4.4 Final note (Important!)
     4.5 Bug-Notes

  5. User experiences
     5.1 Fedora Core 3

  6. Links
     6.1 Ethernet-Bridge
     6.2 Related Topics


  ______________________________________________________________________

  This Howto is available in other formats <http://www.think-
  future.de/DOCUMENTATION/Ethernet-Bridge-netfilter-
  HOWTO/other_formats/>.  Preferably downloadable: documentation tarball
  <http://www.think-future.de/DOCUMENTATION/Ethernet-Bridge-netfilter-
  HOWTO/Ethernet-Bridge-netfilter-HOWTO.tar.gz>.  You may find this
  Howto as part of the Linux Documentation Project
  <http://www.tldp.org/docs.html#howto>.


  Looking for other languages? See the German version <http://www.think-
  future.de/DOCUMENTATION/Ethernet-Bridge-netfilter-HOWTO_de/>, then!
  And as of march 2003 there is a french version available with courtesy
  of François Romieu and Guillaume Lelarge: French version
  <http://fr.tldp.org/HOWTO/lecture/Ethernet-Bridge-netfilter-
  HOWTO.html>.  Today, some day in july 2005, I stumbled across an
  italian version of this HOWTO! Unfortunately there's no translator's
  note in the document, courtesy is unbeknownst so far: Italian version
  <http://ftp-ildp.httpdnet.com/Ethernet-Bridge-netfilter-HOWTO>.


     [1m2005-07-12:[0m
        Added link to italian version of this HOWTO (see above).  Plus a
        section about making the changes ``reboot-persistent'', a note
        about ``2.6 kernel not working as expected'' and the ``user
        experiences-section''.  Included the ``Final note-section''. :)


     [1m2005-06-06:[0m
        Unfortunately, the linux documentation project does not respond
        actively to update requests. This results in an outdated version
        of the on www.tldp.org site. Use this site instead, if you want
        to stick with the most actual version of the HOWTO.  Blame the
        tldp people.


     [1m2004-08-03:[0m
        Carsten (C DOT Lueth AT fielmann DOT com) has found a variant
        for MS Windows (TM) systems
        <http://www.tecchannel.de/software/1387/0.html>.


     [1m2004-06-13:[0m
        Update on used kernel versions, warning about ``remote
        administering'', ``netfilter debugging'' code.  New translation
        available: French (link c. f. above).  Discontinued german
        version.


     [1m2002-09-19:[0m
        links about ebtables have been updated in the "Related Topics"
        Section. Added note about ``"false positive" br-nf debugging
        output''.


     [1m2002-10-08:[0m
        Added section ``Actual configuration'' and hints about routing
        in ``Setting up the routing'', ``Ping it, Jim!''  , resp.



  [1m1.  Introduction[0m

  Ethernet bridges connect two or more distinct ethernet segments
  transparently.
  An ethernet bridge distributes ethernet frames coming in on one port
  to other ports associated to the bridge interface. This is
  accomplished with brain: Whenever the bridge knows on which port the
  MAC address to which the frame is to be delivered is located it
  forwards this frame only to this only port instead of polluting all
  ports together.

  Ethernet interfaces can be added to an existing bridge interface and
  become then (logical) ports of the bridge interface.

  Putting a netfilter structure on top of a bridge interface renders the
  bridge capable of servicing filtering mechanisms. This way, a
  transparent filtering instance can be created. It even needs no IP
  address assigned to work. Of course, you can assign an IP address to
  the bridge interface for maintenance purposes ( certainly, with ssh
  only ;-).

  The advantage of this system is evident. Transparency alleviates the
  network administrator of the pain of restructuring the network
  topology. And users may not notice the existence of the bridge but
  their connection beeing blocked. Also, users are not disturbed while
  working (think of a company where network connection loss pays alot).

  The other common case is a client beeing connected to the global web
  via a leased router. As the providers seldomly grant administration
  privileges on their leasing hardware, the client cannot change the
  interconnecting configuration. But, of course, the client has a
  network running, and wants to spend at least as possible, he does not
  want to reconfigure his entire network. And he does not need to if he
  uses a bridging device.



  [1m2.  Required software[0m

  This software setup is needed on the ethernet bridge computer.
  According to our ``Testing grounds''.


  [1m2.1.  Featured Linux kernel[0m


  Use of kernel 2.6 is not yet a good idea. Yes, it's astonishing. The
  why the bridging code breaks and where it does so has not yet come to
  my and others attention, I cannot recommend kernels of the 2.6 series.
  You have the clou? Assure yourself the credit, mail the solution to me
  (e-mail address at entry page).  See also  ``Kernel-Notes'' for
  additional information on this. So far, use kernel 2.4 series.
  As of kernel version [4m2.4.18[24m  there's already support for the Ethernet
  Bridge capability built-in. No patches needed so far.  Regarding later
  kernel versions, it must be stated that [4m2.4.23[24m  might be less
  recommendable, especially in conjunction with ebtables and netfilter-
  bridging. Later versions seem advisable.
  The following paragraph is outdated now (2005-07-12) as all we need is
  present in kernel. You may skip this paragraph, it is only retained
  for legacy:
  But if we intend to use netfilter capabilities, because we want to run
  iptables on our new Linux router/fw box, we still need to apply a
  patch.  Any patches needed can be found and downloaded on the
  ``sourceforge Ethernet Bridge homepage''.


       root@bridge:~> cd /usr/src/
       root@bridge:~> wget -c http://bridge.sourceforge.net/devel/bridge-nf/bridge-nf-0.0.7-against-2.4.18.diff
       root@bridge:~> cd /usr/src/linux/
       root@bridge:~> patch -p1 -i ../bridge-nf/bridge-nf-0.0.7-against-2.4.18.diff



  Supposedly we want netfilter support on our bridge interface and we
  have already patched the vanillal kernel we may now activate some
  necessary kernel configuration items. On how to build a private kernel
  image see the CD-Net-Install-HOWTO, Toolbox <http://www.think-
  future.de/DOCUMENTATION/CD-Net-Install-HOWTO/CD-Net-Install-
  HOWTO-4.html#Kernel_Configuration>.  Oh, yeah, it's still in German
  only. Hm, I should fix this some time, but time lacks... Any
  volunteers? (deadly silence is cracking.. ;)

  Nevertheless, we start by now: In


               Code maturity level options


  we activate


               [*] Prompt for development and/or incomplete code/drivers



  and in


               Loadable module support



               [*] Enable loadable module support
               [*]   Set version information on all module symbols
               [*]   Kernel module loader



  Ok, so far so good.  Now, we go to


               Networking options



  and mark


               [*] Network packet filtering (replaces ipchains)
               [ ]   Network packet filtering debugging



     [1mNote:[0m
        Previously, the above debugging option had been selected. For
        now, unless you want your /var/log/-partition being filled up in
        short-time distance, deactivate this option.
        If this options is activated, messages similar to the following
        appear in counts of thousands in dmesg and
        /var/log/{kern.log,debug,syslog,messages}:



     skb: pf=2 (unowned) dev=br0 len=52
     PROTO=6 156.136.32.121:3709 192.168.101.2:112 L=52 S=0x00 I=35470 F=0x4000 T=51
     nf_hook: hook 1 already set.
     skb: pf=2 (unowned) dev=br0 len=52
     PROTO=6 156.136.32.121:3709 192.168.101.2:112 L=52 S=0x00 I=35470 F=0x4000 T=51
     nf_hook: hook 0 already set.
     skb: pf=2 (unowned) dev=br0 len=52
     PROTO=6 192.168.101.11:2828 192.168.101.2:202 L=52 S=0x10 I=63 F=0x4000 T=64
     nf_hook: hook 1 already set.
     skb: pf=2 (unowned) dev=br0 len=52
     PROTO=6 192.168.101.11:2828 192.168.101.2:202 L=52 S=0x10 I=63 F=0x4000 T=64
     nf_hook: hook 3 already set.
     skb: pf=7 (owned) dev=eth1 len=1500



  Furthermore, in


                 IP: Netfilter Configuration  --->



  we mark any item we need as module.  Now the long awaited item: acti-
  vate


               <M> 802.1d Ethernet Bridging



  as well as


               [*]   netfilter (firewalling) support



     [1mNote:[0m
        The above entry is available only if we successfully patched our
        kernel!

  Finally, we just need a successful


       root@bridge:~> make dep clean bzImage modules modules_install



  cycle and we're done.  Don't forget to edit /etc/lilo.conf and do



  root@bridge:~> lilo -t
  root@bridge:~> lilo
  root@bridge:~> reboot



  , though.


     [1mHint:[0m
        Perhaps we might mark our new kernel as the bridge kernel? We vi
        the toplevel Makefile in our kernel sources and edit the head
        line called EXTRAVERSION =.  We may actually set it to, say
        [4mbridge[24m? ;-)
        After the modules_install we find the fresh modules in
        /lib/modules/2.4.18bridge
        For debian users (eventually use export PATCH_THE_KERNEL=YES
        before and --added_patches your_patches with make-kpkg):


          root@bridge:~> make-kpkg --revision=tf.1.0 kernel_image



  [1m2.2.  Userspace tool: brctl[0m

  Once our kernel has the capabilities needed to perform Ethernet Bridge
  and netfilter actions, we prepare the user space tool brctl. brctl is
  the configuration tool we use to ``set up'' anything to suit our
  needs.

  We ``download the source tarball'', unpack it and change directory
  into it.


       root@bridge:~> wget -c http://bridge.sourceforge.net/bridge-utils/bridge-utils-0.9.5.tar.gz
       root@bridge:~> tar xvzf bridge-utils-0.9.5.tar.gz
       root@bridge:~> cd bridge-utils-0.9.5



  At this time, read the README and the files in the doc/ subdirectory.
  Then do a simple make and copy the resulting brctl/brctl executable to
  /sbin/.


       root@bridge:~> make
       root@bridge:~> cp -vi brctl/brctl /sbin/



  This is it. Go for ``Setup'' now.



  [1m2.3.  Kernel-Notes[0m

  Symptom: Anything during setup works but packets do no longer traverse
  as they did in 2.4 the bridge interfaces.
  ipuk s (qasuari_ @ _yahoo.com) wrote (about june 2005):


       [...]
       I have to compile my kernel from 2.4.18-14 to 2.6.0 and activate
       bridge-netfilter&ebtables.
       After compiling, i can't ping from a host to interface of linux box.
       Linux box just have 1 interface.whats wrong with my compilation ???
       [...]



  [1m3.  Set Linux up to serve[0m



  [1m3.1.  Setting up the bridge[0m

  We need Linux to know about the bridge. First tell it that we want one
  virtual ethernet bridge interface: (this is to be executed on host
  bridge, of course.  See ``Testing grounds'')


       root@bridge:~> brctl addbr br0



  Second, we do not need the STP (Spanning Tree Protocol). I.e. we do
  only have one single router, so a loop is highly improbable. We may
  then deactivate this feature.  (Results in less polluted networking
  environment, too):


       root@bridge:~> brctl stp br0 off



  After these preparations, we now do finally some effective commands.
  We add our two (or even more) physical ethernet interfaces. That
  means, we attach them to the just born logical (virtual) bridge inter-
  face br0.


       root@bridge:~> brctl addif br0 eth0
       root@bridge:~> brctl addif br0 eth1



     [1mImportant Note:[0m
        People sent me emails that it would have helped them if I
        stressed more clearly the risk of being cut off. So listen at
        this point to my warnings:
        If you read this, you are one (small) step before you _might_
        cut yourself off your box you are going to subverse to a
        bridging device.
        If you love living on bleeding edges, it is now the instant to
        prepare your first aid material. You will likely need it.
        If you do not have physical access, nor does another person
        within your range:
        DO NOT PROCEED UNLESS YOUR FINGERS LEFT THE KEYBOARD IN FRONT OF
        YOU AND YOUR EYES FIXED REFLECTIVELY SOMETHING OTHER THAN YOUR
        CONSOLE.
        You have been warned, now. No responsability is assumed for
        anything at all.

  Now, our two previously physical ethernet interfaces became a logical
  bridge port each.  Erm, ok, there were and will be the physical
  devices. They are still there, go have a look ;-) But now they became
  part of the logical bridge device and therefore need no IP configura-
  tion any longer. So release the IPs:


       root@bridge:~> ifconfig eth0 down
       root@bridge:~> ifconfig eth1 down
       root@bridge:~> ifconfig eth0 0.0.0.0 up
       root@bridge:~> ifconfig eth1 0.0.0.0 up



  Great! We now have a box w/o any IP attached. So if you were configur-
  ing your future fw/router via TP, go for your local console now ;-))
  You have a serial console? Happy one :-)

     [1mOptional:[0m
        We tell Linux the new (logical) interface and associate one
        single IP with it:


          root@bridge:~> ifconfig br0 10.0.3.129 up



  And we're done.
  Read the ``Important Note''!


  [1m3.2.  Setting up the routing[0m


  In case we are configuring a gateway we enable the forwarding in the
  linux kernel.


       root@bridge:~> echo "1" > /proc/sys/net/ipv4/ip_forward



  Our box already has an IP assigned but no default route. We solve this
  now:

  root@bridge:~> route add default gw 10.0.3.129



  Finally, we should have a working net from, to and through the gate-
  way.


  [1m3.3.  Make it happen again![0m

  Aka: We need the changes to persist reboots.
  To do so, you need some sh-style script and put this in the
  appropriate system boot-up directory: /etc/init.d/
  Secondly, you create the link in your runlevel directory.  The correct
  directory depends on your gusto and of course on your linux
  distribution.  Common runlevel values on workstations are 2, 3 and 5.
  Examples are: /etc/rc?.d/ (replace the ? with the right runlevel)
  Also, you need an idea as when your network interfaces are torn up.
  For now, we assume, your network interfaces are activated at system
  priority S so we need not to care of.  If you ever should feel the
  need to know exactly, look in /etc/rcS.d/.  We just want the bridge to
  be up and operable as soon as possible and so chose our priority to be
  10. (Make sure, no service requiring bridging devices is started
  before, read: with priority-values less than 10)
  For now, we assume, your runlevel is 5:


       root@bridge:~> mv -i bridge.sh /etc/init.d/
       root@bridge:~> cd /etc/rc5.d/
       root@bridge:~> ln -s ../init.d/bridge.sh S10bridge.sh



  Virtually any distribution provides you with some runlevel-checker or
  equivalent tool that assists you in the tedious job of administering
  runlevel links. Consult your distro-documentation on this.
  Hint: debian has update-rc.d, redhat and successors have chkconfig.
  Finally, SuSE evidentally has also it's own tool, too (of which I
  don't recall the name easily..).
  Wondering about the contents of bridge.sh? ;-)



  #!/bin/bash
  PATH="/sbin:/usr/sbin:/usr/local/sbin";
  slaveIfs="1 2 3 4 6 7 8 9 10";
  cmd="$1";
  [ -z "$cmd" ] && cmd="start";
  case "$cmd" in
    start)
      brctl addbr br0;
      brctl stp br0 on;
      brctl addif br0 eth0;
      brctl addif br0 eth1;
      (ifdown eth0 1>/dev/null 2>&1;);
      (ifdown eth1 1>/dev/null 2>&1;);
      ifconfig eth0 0.0.0.0 up;
      ifconfig eth1 0.0.0.0 up;
      ifconfig br0 10.0.3.129 broadcast 10.0.3.255 netmask 255.255.255.0 up ### Adapt to your needs.
      route add default gw 10.0.3.129; ### Adapt to your needs.
      for file in br0 eth0 eth1;
      do
        echo "1" > /proc/sys/net/ipv4/conf/${file}/proxy_arp;
        echo "1" > /proc/sys/net/ipv4/conf/${file}/forwarding;
      done;
      echo "1" > /proc/sys/net/ipv4/ip_forward;
      ;;
    stop)
      brctl delif br0 eth0;
      brctl delif br0 eth1;
      ifconfig br0 down;
      brctl delbr br0;
      #ifup eth0; ### Adapt to your needs.
      #ifup eth1; ### Adapt to your needs.
      ;;
    restart,reload)
      $0 stop;
      sleep 3;
      $0 start;
      ;;
  esac;



  And, yes, make it executable..


       root@bridge:~> chmod 700 /etc/init.d/bridge.sh



  After all, make sure your bridge survives unattended reboots. It's the
  same story as with backups: you should test it before you need it.



  [1m4.  Test your new bridged environment![0m



  [1m4.1.  Testing Grounds[0m

  We imagine this scenario or similar:


                                                                 /\
                 Ethernet           Ethernet           ATM    /-/  \
       ---------          ---------          ---------     /-/      |
       |  Box  |----------|Bridge |----------|Router |-----| Inter-  \
       ---------          ---------          ---------     \  net  ---|
                ^        ^         ^        ^               \     /
                |        |         |        |                \---/
               eth0     eth0      eth1     if0                 ^
                |        |         |        |                  |
             10.0.3.2   none/10.0.3.1      195.137.15.7    anything else
                         \         /
                          \       /
          ^                \-br0-/
          |                                      ^             ^
          |                   ^                  |             |
          |                   |                  |             |
         own                 own              foreign        hostile



  Our administrative power includes only machines marked with own, the
  Router is completely off-limits and so is the Internet, of course.
  That means, if we want to control the flying bits'n'bytes on the eth-
  ernet wire we can chose to integrate a common firewall or file in a
  bridge.
  Drawback of the standard way is you have to change the default gateway
  route on every and any single host in your net. And this is really a
  heavy weighting drawback, nobody wants to change more than 5 default
  routes on 5 different hosts more than one time. Keep the time in mind,
  this will consume, also! Not to forget, this is a error-prone way to
  handle the more about security..
  The other way is clean, less time-consuming, more secure and less
  error-prone.  More secure in that we won't have the need to assign any
  IP address. No IP, no danger.  So far the theory, we hope, our stacks
  are safe. (Although this hope should better not relied on..) The over-
  all advantage is, this bridge-setup is completely transparent, no IP,
  MAC, .. changes at all.
  So it's up to you to chose your preferred method. But we will handle
  just the fancy one here ;-)



  [1m4.2.  Ping it, Jim![0m

  We will configure the Box' eth0 as usual. The bridge's interfaces are
  configured as described in ``Setup''.

  If we are to use forwarding we might perhaps do this one: ;-)


       root@bridge:~> echo "1" > /proc/sys/net/ipv4/ip_forward



  Optionally, we set up a default route:


  root@bridge:~> route add default gw 10.0.3.129



  Then we set up some iptables rules on host bridge:



       root@bridge:~> iptables -P FORWARD DROP
       root@bridge:~> iptables -F FORWARD
       root@bridge:~> iptables -I FORWARD -j ACCEPT
       root@bridge:~> iptables -I FORWARD -j LOG
       root@bridge:~> iptables -I FORWARD -j DROP
       root@bridge:~> iptables -A FORWARD -j DROP
       root@bridge:~> iptables -x -v --line-numbers -L FORWARD



  The last line gives us the following output:


       Chain FORWARD (policy DROP 0 packets, 0 bytes)
       num      pkts      bytes target   prot opt in     out     source   destination
       1           0        0 DROP       all  --  any    any     anywhere anywhere
       2           0        0 LOG        all  --  any    any     anywhere anywhere      LOG level warning
       3           0        0 ACCEPT     all  --  any    any     anywhere anywhere
       4           0        0 DROP       all  --  any    any     anywhere anywhere



  The LOG target logs every packet via syslogd. Beware, this is intended
  for testing purposes only, remove in production environment. Else you
  end up either with filled logs and harddisk partitions by you yourself
  or anyone else does this Denial of Service to you. You've been warned.
  Test this ruleset now. Ping the router interface's IP (195.137.15.7)
  on host box:


       root@box:~> ping -c 3 195.137.15.7
       PING router.provider.net (195.137.15.7) from 10.0.3.2 : 56(84) bytes of data.
       --- router.provider.net ping statistics ---
       3 packets transmitted, 0 received, 100% loss, time 2020ms
       ^C
       root@box:~>



  By default, we DROP everything. No response, no logged packet. This
  netfilter setup is designed to DROP all packets unless we delete the
  rule that drops every packet (rule no. 1 above) before the LOG target
  matches:


       root@bridge:~> iptables -D FORWARD 1
       root@bridge:~> iptables -x -v --line-numbers -L FORWARD



  Now, the rules are:


       Chain FORWARD (policy DROP 0 packets, 0 bytes)
       num      pkts      bytes target   prot opt in     out     source   destination
       2           0        0 LOG        all  --  any    any     anywhere anywhere      LOG level warning
       3           0        0 ACCEPT     all  --  any    any     anywhere anywhere
       4           0        0 DROP       all  --  any    any     anywhere anywhere



  And any packet may pass through. Test it with a ping on host box:


       root@box:~> ping -c 3 195.137.15.7
       PING router.provider.net (195.137.15.7) from 10.0.3.2 : 56(84) bytes of data.
       64 bytes from router.provider.net (195.137.15.7): icmp_seq=1 ttl=255 time=0.103 ms
       64 bytes from router.provider.net (195.137.15.7): icmp_seq=2 ttl=255 time=0.082 ms
       64 bytes from router.provider.net (195.137.15.7): icmp_seq=3 ttl=255 time=0.083 ms

       --- router.provider.net ping statistics ---
       3 packets transmitted, 3 received, 0% loss, time 2002ms
       rtt min/avg/max/mdev = 0.082/0.089/0.103/0.012 ms
       root@box:~>



  Yippeah! The router is alive, up and running. (Well it has been all
  day long.. ;-)


     [1mImportant Note:[0m

        When we just fired up the bridge interface it takes about
        roughly 30 seconds until the bridge is fully operational. This
        is due the 30-seconds-learning phase of the bridge interface.
        During this phase, the bridge ports are learning what MAC
        addresses exist on what port. The bridge author, Lennert, tells
        us in his TODO file, the 30-seconds-learning phase is subjected
        to some improvement in a timely manner some time.
        During the test phase, no packet will we forwarded. No ping be
        answered.  Remind this!


  [1m4.3.  Actual configuration[0m


  This section is intended to give you, dear reader, some hints about
  how your system should look and feel after having processed this howto
  successfully.


  [1m4.3.1.  Interface configuration[0m

  The output of your ifconfig command might look similar to this:



  root@bridge:~> ifconfig
  br0       Link encap:Ethernet  HWaddr 00:04:75:81:D2:1D
            inet addr:10.0.3.129  Bcast:195.30.198.255  Mask:255.255.255.128
            UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
            RX packets:826 errors:0 dropped:0 overruns:0 frame:0
            TX packets:737 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:0
            RX bytes:161180 (157.4 Kb)  TX bytes:66708 (65.1 Kb)

  eth0      Link encap:Ethernet  HWaddr 00:04:75:81:ED:B7
            UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
            RX packets:5729 errors:0 dropped:0 overruns:0 frame:0
            TX packets:3115 errors:0 dropped:0 overruns:0 carrier:656
            collisions:0 txqueuelen:100
            RX bytes:1922290 (1.8 Mb)  TX bytes:298837 (291.8 Kb)
            Interrupt:11 Base address:0xe400

  eth1      Link encap:Ethernet  HWaddr 00:04:75:81:D2:1D
            UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
            RX packets:0 errors:0 dropped:0 overruns:1 frame:0
            TX packets:243 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:100
            RX bytes:342 (342.0 b)  TX bytes:48379 (47.2 Kb)
            Interrupt:7 Base address:0xe800

  lo        Link encap:Local Loopback
            inet addr:127.0.0.1  Mask:255.0.0.0
            UP LOOPBACK RUNNING  MTU:16436  Metric:1
            RX packets:1034 errors:0 dropped:0 overruns:0 frame:0
            TX packets:1034 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:0
            RX bytes:82068 (80.1 Kb)  TX bytes:82068 (80.1 Kb)



  [1m4.3.2.  Routing configuration[0m

  The output of your route command might look similar to this:


       root@bridge:~> route -n
       Kernel IP routing table
       Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
       10.0.3.129      0.0.0.0         255.255.255.128 U     0      0        0 br0
       0.0.0.0         10.0.3.129      0.0.0.0         UG    0      0        0 br0
       root@bridge:~>



  [1m4.3.3.  Iptables configuration[0m

  Please have a look at the ``Ping it, Jim!'' section.


  [1m4.4.  Final note (Important!)[0m

  I'd like to hear from you! :-)
  Did you enjoy the trip?
  Do you miss anything?
  Need help? (Call you local assistant ;-) or rtfm.
  You are still online? Then drop me a msg via email. I'd be really
  glad.
  Wanna send me a cheque? Pitty, Don't accept these.. (Just kidding;)
  Make it worth my time, just send me some nice words, that's enough.
  Nothing motivates more than happy participants giving you valuable
  feedback.
  So, go on, invest a minute and hack me a mail!
  Thank you!



       Nils



  [1m4.5.  Bug-Notes[0m


  Apparently, there must have been a bug in the br-nf code:


       From: Bart De Schuymer <bart.de.schuymer_@_pandora.be>
       Date: Sun, 1 Sep 2002 21:52:46 +0200
       To: Nils Radtke <Nils.Radtke_@_Think-Future.de>
       Subject: Re: Ethernet-Brigde-netfilter-HOWTO

       Hello Nils,

       [...]
       Also, network packet filtering debugging is generally a bad idea with the
       br-nf patch. It can gives a lot of false warnings (about bugs) in the logs.
       [...]



  Personally, I never had false positives in my log. Maybe, that bug has
  been fixed. This mailed to Bart, he wrote:


       From: Bart De Schuymer <bart.de.schuymer_@_pandora.be>
       Date: Mon, 2 Sep 2002 18:30:25 +0200
       To: Nils Radtke <Nils.Radtke_@_Think-Future.de>
       Subject: Re: Ethernet-Brigde-netfilter-HOWTO

       On Monday 02 September 2002 00:39, Nils Radtke wrote:
       > Will the revision of the nf-debug code in br-nf be subject of improvement?

       I must admit I haven't been running any kernel with netfilter debugging
       lately. It sure used to give false positives a few months ago (the bridge
       mailing list has posts about that), I've been lacking time to see why and if
       it is still the case. It's on my todo list.
       [...]



  But (as of writing this 2002-09-19) I haven't found an official
  announcement, this particular bug has been closed. So have a constant
  look at this topic on the ``ethernet bridge mailinglist'' , if you are
  interested in it's cure.



  [1m5.  User experiences[0m


  [1m5.1.  Fedora Core 3[0m

  James Dinkel (jdinkel_ @ _gmail.com) wrote on Tue, 8 Mar 2005 10:59:22
  -0600:


       [...]
       I am using Fedora Core 3 and all I had to do was "yum install bridge-utils"
       to use the brctl command. I didn't have to do any kernel recompiling or
       configurations or messing with kernel modules.
       It was very easy.
       [...]



  [1m6.  Links[0m

  The Howto's author may be contacted via e-mail <mailto:Ethernet-
  Bridge-netfilter-Howto_@_Think-Future.de>.
  Howto Author's homepage <http://Think-Future.de/>.


  [1m6.1.  Ethernet-Bridge[0m


  ·   Ethernet Bridge Mailinglist
     <http://www.math.leidenuniv.nl/pipermail/bridge/>

  ·   User space utilities, patches, etc.: Home of Linux kernel Ethernet
     Bridge <http://bridge.sourceforge.net>

  ·   Bridge-STP-HOWTO <http://www.tldp.org/HOWTO/BRIDGE-STP-
     HOWTO/index.html>

  ·   Firewalling for Free, Shawn Grimes
     <./additional_docs/Firewalling_for_Free.pdf>



  [1m6.2.  Related Topics[0m


  ·  Filtering on frame level, Ethernet-Bridging-Tables:
     ebtables, sourceforge <http://sourceforge.net/projects/ebtables>
     ebtables, supported features
     <http://users.pandora.be/bart.de.schuymer/ebtables/properties.html>
     ebtables, examples: basic
     <http://users.pandora.be/bart.de.schuymer/ebtables/examples.html>,
     advanced
     <http://users.pandora.be/bart.de.schuymer/ebtables/battlefield_examples.html>

  ·  IP mode, Linux Bridge extension: IP mode, LVS
     <http://www.ssi.bg/~ja/>
  ·  Linux in High-Availability environments: High-Availability Linux
     <http://www.linux-ha.org/>

  ·  Linux Virtual Server: LVS <http://www.linuxvirtualserver.org/>



