<!DOCTYPE ARTICLE PUBLIC "-//OASIS//DTD DocBook V4.1//EN"[]>

<article>
<title>Bridging mini-HOWTO</title>
<!-- Title information -->
<articleinfo>
    <author>
        <firstname>Christopher </firstname>
        <surname>Cole</surname>
      <affiliation>
          <address>
            <email>cole@coledd.com</email>
          </address>
      </affiliation>
    </author>
<author>
<firstname>Vertaald door: Ellen</firstname>
<surname>Bokhorst</surname>
<affiliation>
<address>
<email>bokkie@nl.linux.org</email>
</address>
</affiliation>
</author>
<pubdate>Maart 2001</pubdate>
<revhistory>
      <revision>
	<revnumber>1.22</revnumber>
	<date>20-05-2002</date>
	<authorinitials>tab</authorinitials>
	<revremark>Naar DocBook 4.1 geconverteerd en GFDL per Christopher
Cole toegevoegd</revremark>
      </revision>
      <revision>
        <revnumber>1.21</revnumber>
        <date>07-03-2001</date>
	<authorinitials>cc</authorinitials>
      </revision>
</revhistory>
<abstract>
<para>In dit document wordt beschreven hoe een ethernet bridge op te zetten.
Wat is een ethernet bridge? Een ethernet bridge is een device dat 
datapackets bestuurt binnen een subnet in een poging de hoeveelheid
verkeer te beperken. Een bridge wordt gewoonlijk tussen twee aparte
groepen computers geplaatst welke binnen die groep communiceren, maar
niet zoveel met de computers in de andere groep.
Een goed voorbeeld hiervan is te zien in een cluster met Macintosh machines
en een cluster unix machines. Beiden groepen machines neigen nogal 
babbelziek onder elkaar te zijn, en het verkeer dat ze op het netwerk
produceren, veroorzaakt aanvaringen met de andere machines die met
elkaar proberen te communiceren. Tussen deze groepen computers zou een
bridge worden geplaatst. De taak van de bridge bestaat uit het &eacute;&eacute;n
voor &eacute;&eacute;n bestuderen van de bestemming van de datapakketjes
en te besluiten of het de pakketjes wel of niet aan de andere kant van
het ethernetsegment zal doorgeven.
Het resultaat is een sneller, stiller netwerk met minder aanvaringen.
</para>
</abstract>
</articleinfo>
<!-- Table of contents -->


<sect1>
  <title>Setup</title>
<para>
 <itemizedlist>
  <listitem>
    <para>Haal Bridge Config op:
    <ulink url="ftp://ftp.tux.org/people/alan-cox/BRCFG.tgz"> BRCFG.tgz</ulink>
    </para>
  </listitem>

  <listitem>
    <para>BRCFG is ook te vinden op:
    <ulink url="http://coledd.com/networking/bridge/"> http://coledd.com/networking/bridge</ulink>
    </para>
  </listitem>

  <listitem>
    <para>Activeer meerdere ethernet devices op je machine door
deze regel toe te voegen aan het bestand <filename>/etc/lilo.conf</filename>,
        en <application>lilo</application> uit te voeren:
        <screen>append = "ether=0,0,eth1"</screen>
    </para>
    <para>Als je drie interfaces op je bridge hebt, gebruik dan in plaats
daarvan deze regel:
        <screen>append = "ether=0,0,eth1 ether=0,0,eth2"</screen>
    </para>
    <para>Er kunnen meer interfaces worden gevonden door meer ether statements
toe te voegen. Standaard detecteert een Linux kernel een enkele ethernetkaart,
en zodra er &eacute;&eacute;n wordt gevonden, stopt de detectie.
De bovenstaande append opdracht vertelt de kernel te blijven zoeken naar
meer ethernet devices nadat de eerste werd gevonden.
Als alternatief kan daarvoor in de plaats een bootparameter worden gebruikt:
        <screen>linux ether=0,0,eth1</screen>
    </para>
    <para>Of, gebruik bij 3 interfaces:
        <screen>linux ether=0,0,eth1 ether=0,0,eth2</screen>
    </para>
  </listitem>

  <listitem>
    <para>Hercompileer de kernel met <envar>BRIDGING</envar> geactiveerd.
    </para>
  </listitem>

  <listitem>
<para>Een bridge heeft geen IP-adres nodig. Het kan wel, maar
voor een gewone bridge hoeft dat niet. Ga (bij een RedHat systeem) naar
<filename>/etc/sysconfig/network-scripts/</filename> 
en kopieer 
<filename>ifcfg-lo0</filename> naar <filename>ifcfg-eth0</filename> &amp;
        <filename>ifcfg-eth1</filename> om het IP-adres uit je bridge
te verwijderen.
        Wijzig in deze twee nieuwe bestanden de regel met daarin
        <userinput>DEVICE=lo</userinput> in <userinput>DEVICE=eth0</userinput>
        en <userinput>DEVICE=eth1</userinput>.
Aangezien andere distributies hiervan kunnen afwijken, moet je wellicht
aanvullende documentatie raadplegen.
Als er meer dan 2 interfaces naar deze bridge zijn, zorg dan dat je
de corresponderende configuraties ook daarin maakt.
</para>
  </listitem>

  <listitem>
<para>
Reboot zodat je de nieuwe kernel met <envar>BRIDGING</envar> draait,
en zorg er ook voor dat er geen IP-adressen zijn verbonden met de
netwerkinterfaces.
    </para>
  </listitem>

  <listitem>
    <para>Plaats de ethernetkaarten in promiscuous modus zodra een
backup van het systeem is gemaakt, zodat ze elk pakket dat de interfaces
passeert bekijken:
        <screen>ifconfig eth0 promisc ; ifconfig eth1 promisc</screen>
        Alle interfaces die zijn verbonden met netwerksegmenten
aan de bridge worden in promiscuous modus geplaatst.
    </para>
  </listitem>

  <listitem>
    <para>Zet bridging aan met behulp van het programma 
<application>brcfg</application>:
        <screen>brcfg -ena</screen>
    </para>  
  </listitem>

  <listitem>
    <para>Verifieer dat er ander verkeer op elke interface is:
    <screen>
tcpdump -i eth0     (in een venster)
tcpdump -i eth1     (in een ander venster)
    </screen>
    </para>
  </listitem>      

  <listitem>
    <para>Start een sniffer of <application>tcpdump</application> op
een andere machine om te verifi&euml;ren dat de bridge het segment correct
scheidt.
    </para>
  </listitem>
</itemizedlist>
</para>
</sect1>


<sect1>
<title>Algemene Problemen</title>

    <qandaset defaultlabel='qanda'>
      <qandaentry>
      <question>
        <para>Ik krijg de melding <errorname>ioctl(SIOCGIFBR) failed: Package not installed
        </errorname>.  Wat betekent dit?</para>
      </question>
      <answer>
        <para>Je hebt de bridging mogelijkheid niet in je kernel.
        Haal een 2.0 of nieuwere kernel op, en compileer het met
        de optie <envar>BRIDGING</envar> geactiveerd.</para>
      </answer>
      </qandaentry>
  
      <qandaentry>
      <question>
        <para>Machines aan de ene kant kunnen de andere kant niet pingen!</para>
      </question>
      <answer>
        <itemizedlist spacing=compact>
          <listitem><simpara>Heb je bridging met behulp van het programm
<application>brcfg -ena</application> geactiveerd? 
(<application>brcfg</application> zou 
<returnvalue>bridging is ENABLED</returnvalue> aan moeten geven) </simpara>
          </listitem>
          <listitem><simpara>Heb je de interfaces in promiscuous modus
geplaatst?
                (roep de opdracht <application>ifconfig</application> aan.
                 De vlag <property>PROMISC</property> zou aan moeten staan
bij beide interfaces.)</simpara>
          </listitem>
          <listitem><simpara>Als je multiple-media interface-adapters
gebruikt, zorg dan dat de juiste is geactiveerd.
                Wellicht dat je het config/setup programma moet gebruiken
dat met de netwerkinterfacekaart werd meegeleverd.
                </simpara>
          </listitem>
        </itemizedlist>
      </answer>
      </qandaentry>

      <qandaentry>
      <question>
        <para>Ik kan niet <application>telnetten</application>/<application>ftp'en</application> vanaf de bridge! Waarom niet?</para>
      </question> 
      <answer>
        <para>Dit komt doordat er geen IP-adres is verbonden met een van
de bridge interfaces. Een bridge dient een transparant deel van een netwerk
te zijn.
        </para>
     </answer>
     </qandaentry>

     <qandaentry>
     <question>
	<para>Wat heb ik nodig om de wijze van routing op te zetten?</para>
     </question>	
     <answer>
        <para>Niets!
        Alle routing intelligentie wordt afgehandeld door de bridging code
in de kernel. Gebruik het programma <application>brcfg</application>
in debug modus om de ethernetadressen te zien zoals ze door de bridge worden
geleerd:
        </para>
        <screen>
brcfg -deb
        </screen>
     </answer>
     </qandaentry>

     <qandaentry>
     <question>
        <para>De bridge schijnt te werken, maar waarom toont 
<application>traceroute</application> de bridge niet als onderdeel van het pad?</para>
     </question>
     <answer>
        <para>Vanwege de aard van een bridge hoort <application>traceroute</application> de bridge niet als onderdeel van het pad te tonen. Een bridge
dient als een transparante component van het netwerk.</para>
     </answer>
     </qandaentry>

     <qandaentry>
     <question>
        <para>Is het noodzakelijk <envar>IP_FORWARD</envar> in de kernel te
compileren?</para>
     </question>
     <answer>
        <para>Nee. De bridging code in de kernel zorgt voor het transport
van pakketjes.
        <envar>IP_FORWARD</envar> is voor een gateway die IP-adressen
aan zijn interfaces heeft verbonden.
        </para>
     </answer>
     </qandaentry>

     <qandaentry>
     <question>
        <para>Waarom zijn de fysieke ethernetadressen voor poort 1 en
poort 2 hetzelfde volgens het programma
        <application>brcfg</application>?
        Zouden ze niet verschillend moeten zijn?</para>
     </question> 
     <answer>
        <para>Nee. Aan elke poort van een bridge wordt door de bridging 
code expres hetzelfde fysieke ethernetadres toegekend.
        </para>
     </answer>
     </qandaentry>

     <qandaentry>
     <question>
        <para>Bridging verschijnt niet als optie wanneer een make config
op de kernel uitvoert.
        Hoe activeert men dit?</para>
     </question>
     <answer>
        <para>Antwoord tijdens de kernelconfig <quote>Y</quote> op de vraag
<prompt>Prompt for development and/or incomplete code/drivers (CONFIG_EXPERIMENTAL) [Y/n/?]</prompt>.</para>
     </answer>
     </qandaentry>

     <qandaentry>
     <question>
        <para>Te veel hubs (4 of meer) zijn na elkaar in serie geketend,
wat op een ethernet voor timing problemen zorgt. Welk effect heeft een
bridge in een subnet dat met hubs in lagen werkt?</para>
     </question>
     <answer>
        <para>Een bridge reset de 3/4/5 hubs rule. Een bridge gaat niet
zo om met pakketjes zoals een hub dat doet,  en draagt daarom niet bij
aan timing problemen op een netwerk.
        </para>
     </answer>
     </qandaentry>

     <qandaentry>
     <question>
        <para>Kan een bridge interface naar zowel 10Mb als 100Mb 
ethernetsegmenten? Zal een dergelijke configuratie de rest van het
verkeer op de hoge snelheidslijn vertragen?
        </para>
     </question>
     <answer>
        <para>Je, een bridge kan een 10Mb segment aan een 100Mb segment
verbinden. Zolang als de netwerkkaart op het snelle netwerk  100Mb capabel
is, zorgt TCP voor de rest. Ondanks dat het klopt dat de pakketjes van
een host in het 100Mb netwerk die communiceert met een host in het
10Mb netwerk slechts met een snelheid van 10Mb's worden verplaatst, wordt
de rest van het verkeer op het snelle ethernet niet vertraagd.
        </para>
     </answer>
     </qandaentry>
    </qandaset>

</sect1>

<sect1>
<title>Copyright</title>
<para>Copyright &copy; 2002 Christopher Cole</para>
<para>Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts.  A copy of the license is included in the section entitled "GNU Free Documentation License".</para>


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<para>Version 1.1, March 2000</para>

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<para>You may extract a single document from such a collection,
    and distribute it individually under this License, provided you
    insert a copy of this License into the extracted document, and
    follow this License in all other respects regarding verbatim
    copying of that document.</para>
</sect2>

<sect2 id="gfdl-7">
<title>AGGREGATION WITH INDEPENDENT WORKS</title>
<para>A compilation of the Document or its derivatives with other
    separate and independent documents or works, in or on a volume of
    a storage or distribution medium, does not as a whole count as a
    Modified Version of the Document, provided no compilation
    copyright is claimed for the compilation.  Such a compilation is
    called an "aggregate", and this License does not apply to the
    other self-contained works thus compiled with the Document, on
    account of their being thus compiled, if they are not themselves
    derivative works of the Document.</para>

<para>If the Cover Text requirement of section 3 is applicable to
    these copies of the Document, then if the Document is less than
    one quarter of the entire aggregate, the Document's Cover Texts
    may be placed on covers that surround only the Document within the
    aggregate.  Otherwise they must appear on covers around the whole
    aggregate.</para>
</sect2>

<sect2 id="gfdl-8">
<title>TRANSLATION</title>

<para>Translation is considered a kind of modification, so you may
    distribute translations of the Document under the terms of section
    4.  Replacing Invariant Sections with translations requires
    special permission from their copyright holders, but you may
    include translations of some or all Invariant Sections in addition
    to the original versions of these Invariant Sections.  You may
    include a translation of this License provided that you also
    include the original English version of this License.  In case of
    a disagreement between the translation and the original English
    version of this License, the original English version will
    prevail.</para>
</sect2>

<sect2 id="gfdl-9">
<title>TERMINATION</title>
<para>You may not copy, modify, sublicense, or distribute the
    Document except as expressly provided for under this License.  Any
    other attempt to copy, modify, sublicense or distribute the
    Document is void, and will automatically terminate your rights
    under this License.  However, parties who have received copies, or
    rights, from you under this License will not have their licenses
    terminated so long as such parties remain in full
    compliance.</para>
</sect2>

<sect2 id="gfdl-10">
<title>FUTURE REVISIONS OF THIS LICENSE</title>

<para>The Free Software Foundation may publish new, revised
    versions of the GNU Free Documentation License from time to time.
    Such new versions will be similar in spirit to the present
    version, but may differ in detail to address new problems or
    concerns.  See <ulink
    url="http://www.gnu.org/copyleft/">http://www.gnu.org/copyleft/</ulink>.</para>

<para>Each version of the License is given a distinguishing
    version number.  If the Document specifies that a particular
    numbered version of this License "or any later version" applies to
    it, you have the option of following the terms and conditions
    either of that specified version or of any later version that has
    been published (not as a draft) by the Free Software Foundation.
    If the Document does not specify a version number of this License,
    you may choose any version ever published (not as a draft) by the
    Free Software Foundation.</para>
</sect2>

<sect2 id="gfdl-11">
<title>How to use this License for your documents</title>

<para>To use this License in a document you have written, include
    a copy of the License in the document and put the following
    copyright and license notices just after the title page:</para>

<blockquote><para>
Copyright (c)  YEAR  YOUR NAME.
      Permission is granted to copy, distribute and/or modify this document
      under the terms of the GNU Free Documentation License, Version 1.1
      or any later version published by the Free Software Foundation;
      with the Invariant Sections being LIST THEIR TITLES, with the
      Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
      A copy of the license is included in the section entitled "GNU
      Free Documentation License".
</para></blockquote>

<para>If you have no Invariant Sections, write "with no Invariant
    Sections" instead of saying which ones are invariant.  If you have
    no Front-Cover Texts, write "no Front-Cover Texts" instead of
    "Front-Cover Texts being LIST"; likewise for Back-Cover
    Texts.</para>

<para>If your document contains nontrivial examples of program
    code, we recommend releasing these examples in parallel under your
    choice of free software license, such as the GNU General Public
    License, to permit their use in free software.</para>
</sect2>
</sect1>
</article>