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diff --git a/docbook/wsug_src/WSUG_chapter_troubleshoot.xml b/docbook/wsug_src/WSUG_chapter_troubleshoot.xml new file mode 100644 index 0000000000..999c960fca --- /dev/null +++ b/docbook/wsug_src/WSUG_chapter_troubleshoot.xml @@ -0,0 +1,129 @@ +<!-- WSUG Chapter Four --> +<!-- $Id$ --> + +<chapter id="Chap04"> + <title>Troubleshooting with <application>Ethereal</application></title> + <section> + <title>An approach to troubleshooting with Ethereal</title> + <para> + Wireshark is a very useful tool for network troubleshooting, since it + contains a number of features that allow you to quickly focus on + problems in your networkfor several reasons: + <itemizedlist> + <listitem> + <para> + It allows you to focus in on specific packets and protocols, + as you can see a large amount of detail associated with + various protocols. + </para> + </listitem> + <listitem> + <para> + It supports a large number of protocols, and the list of + protocols supported is growing as more people contribute + dissectors + </para> + </listitem> + <listitem> + <para> + By giving you a visual view of traffic in parts of your + network, and providing tools to filter and colorize that + information, you can get a better feel for your network + traffic, and can understand your network better. + </para> + </listitem> + </itemizedlist> + </para> + <para> + The following general approach is suggested: + <itemizedlist> + <listitem> + <para> + Determine that the problem looks like a networking problem. + There is no point in capturing packets if the problem is not + networking related. + </para> + </listitem> + <listitem> + <para> + Figure out where to capture packets. You will have to + capture packets from a part of the network where you can + actually get network traffic related to the problem. This is + especially important in the presence of switches and routers. + See <xref linkend="Ch04ROUSWI"/> for more details. + </para> + <para> + Because Ethereal can read many capture file formats, you can + capture using any conventient tool. One useful approach is + to use <command>tcpdump</command> to capture on remote + systems and then copy the capture file to your system for + later analysis. For more details on capturing with + <command>tcpdump</command>, see <xref linkend="Ch05tcpdump"/>. + </para> + </listitem> + <listitem> + <para> + Once you have captured packets that you think relate to + the problem, load them into Ethereal and look for your + problem. Using Ethereal's filtering and colorization + capabilities, you can quickly narrow down the capture to the + area of interest. + </para> + </listitem> + <listitem> + <para> + Examine the appropriate fields within the packets where + the problem appears to be. These can often help to reveal + the problem. + </para> + </listitem> + </itemizedlist> + </para> + </section> + <section id="Ch04ROUSWI"> + <title>Capturing in the presence of switches and routers</title> + <para> + In the old days of Ethernet, all network traffic was spreaded over one + "yellow" cable through the whole network. Capturing data was easy, + as all packets from the network could be captured using the + "promiscuous mode" at any place in the network. The only devices blocking + network traffic, were routers. But as routers were extremely expensive, + they were not widely used. + </para> + <para> + Then Ethernet wiring using hubs become the state of the art. As the hubs + still spreaded the packets all over the network, things regarding + capturing didn't changed. + </para> + <para> + At the next stage, Ethernet switches became widely available. This + complicated things a lot. When capturing traffic on a computer connected + to a switch, usually the switch will only forward packets to the computer, + which are directed to it, or to all computers (broadcast's). It's much the + same like deactivating the promiscuous mode of the capturing network card. + </para> + <para> + There are some ways to circumvent this. + </para> + <para> + Many vendor's switches support a feature known as "port spanning" + or "port mirroring" in which all of the traffic to and from port A + are also sent out port B. An excellent reference on the + "port spanning" feature of Cisco switches can be found at + <ulink url="http://www.cisco.com/warp/public/473/41.html"> + Configuring the Catalyst Switched Port Analyzer (SPAN) Feature + </ulink> + </para> + </section> + <section> + <title>Examples of troubleshooting</title> + <para> + Troubleshooting often requires a reasonable knowledge of the + protocols in question. However, as Ethereal will often give you some + good hints, you might get an idea of what is going wrong simply by + looking in the packets being exchanged. + </para> + </section> +</chapter> +<!-- End of WSUG Chapter 4 --> + |