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147 lines
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<meta name="DC.Title" content="Troubleshoot VPN with the communications trace" />
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<title>Troubleshoot VPN with the communications trace</title>
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<body id="rzajacomtrac"><a name="rzajacomtrac"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Troubleshoot VPN with the communications trace</h1>
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<div><p></p>
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<p><span class="keyword">IBM<sup>®</sup> i5/OS™</span> provides
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the capability to trace data on a communications line, such as a local area
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network (LAN) or wide area network (WAN) interface. The average user may not
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understand the entire contents of the trace data. However, you can use the
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trace entries to determine whether a data exchange between the local and the
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remote systems took place.</p>
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<div class="section"><h4 class="sectiontitle">Starting the communications trace</h4><p>Use the Start
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Communications Trace (STRCMNTRC) command to start the communications trace
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on your system. The following is an example of the STRCMNTRC command:</p>
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<pre>STRCMNTRC CFGOBJ(TRNLINE) CFGTYPE(*LIN) MAXSTG(2048) TEXT('VPN Problems')</pre>
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<p>The command parameters are explained in the following list:</p>
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<dl><dt class="dlterm">CFGOBJ (Configuration object)</dt>
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<dd>The name of the configuration object to trace. The object is either a
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line description, a network interface description, or a network server description.</dd>
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<dt class="dlterm">CFGTYPE (Configuration type)</dt>
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<dd>Whether a line (*LIN), a network interface (*NWI), or a network server
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(*NWS) is being traced.</dd>
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<dt class="dlterm">MAXSTG (Buffer size)</dt>
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<dd>The buffer size for the trace. The default value is set to 128 KB. The
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range goes from 128 KB to 64 MB. The actual maximum system-wide buffer size
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is defined within the System Service Tools (SST). Therefore, you may receive
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an error message when using a larger buffer size on the STRCMNTRC command
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than defined in the SST. Keep in mind that the sum of buffer sizes specified
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on all started communications traces must not exceed the maximum buffer size
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defined in the SST.</dd>
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<dt class="dlterm">DTADIR (Data direction )</dt>
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<dd>The direction of data traffic to be traced. The direction can be outbound
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traffic only (*SND), inbound traffic only (*RCV), or both directions (*BOTH).</dd>
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<dt class="dlterm">TRCFULL (Trace full )</dt>
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<dd>What occurs when the trace buffer is full. This parameter has two possible
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values. The default value is *WRAP, which means, when the trace buffer is
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full, the trace wraps to the beginning. The oldest trace records are written
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over by new ones as they are collected.<p>The second value *STOPTRC let the
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trace stop when the trace buffer, specified in the MAXSTG parameter is full
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of trace records. As general rule, always define the buffer size to be large
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enough to store all the trace records. If the trace wraps, you may lose important
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trace information. If you experience a highly intermittent problem, define
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the trace buffer to be large enough that a wrap of the buffer will not discard
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any important information.</p>
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</dd>
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<dt class="dlterm">USRDTA (Number of user bytes to trace)</dt>
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<dd>Defines the number of data to be traced in the user data part of the data
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frames. By default only the first 100 bytes of user data are captured for
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LAN interfaces. For all other interfaces, all user data is captured. Make
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sure you specify *MAX if you suspect problems in the user data of a frame.</dd>
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<dt class="dlterm">TEXT (Trace description)</dt>
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<dd>Provides a meaningful description of the trace.</dd>
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</dl>
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</div>
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<div class="section"><h4 class="sectiontitle">Stopping the communications trace</h4><p>If you do not
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otherwise specify, the trace typically stops as soon as the condition for
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which you are tracing occurs. Use the End Communications Trace (ENDCMNTRC)
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command to stop the trace. The following command is an example of the ENDCMNTRC
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command:</p>
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<pre>ENDCMNTRC CFGOBJ(TRNLINE) CFGTYPE(*LIN)</pre>
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<p>The
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command has two parameters:</p>
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<dl><dt class="dlterm">CFGOBJ (Configuration object)</dt>
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<dd>The name of the configuration object for which the trace is running. The
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object is either a line description, a network interface description, or a
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network server description.</dd>
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<dt class="dlterm">CFGTYPE (Configuration type )</dt>
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<dd>Whether a line (*LIN), a network interface (*NWI), or a network server
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(*NWS) is being traced.</dd>
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</dl>
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</div>
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<div class="section"><h4 class="sectiontitle">Printing the trace data</h4><p>After you stop the communications
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trace, you need to print the trace data. Use the Print Communications Trace
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(PRTCMNTRC) command to perform this task. Since all line traffic is captured
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during the trace period, you have multiple filter options for output generation.
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Try to keep the spooled file as small as possible. This makes the analysis
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faster and more efficient. In the case of a VPN problem, filter on IP traffic
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only and, if possible, on a specific IP address. You also have the option
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of filtering on a specific IP port number. The following is an example of
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the PRTCMNTRC command:</p>
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<pre>PRTCMNTRC CFGOBJ(TRNLINE) CFGTYPE(*LIN) FMTTCP(*YES) TCPIPADR('10.50.21.1)
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SLTPORT(500) FMTBCD(*NO)</pre>
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<p>In this example, the trace is formatted
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for IP traffic and contains only data for the IP address, where the source
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or destination address is 10.50.21.1 and the source or destination IP port
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number is 500.</p>
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<p>Only the most important command parameters for analyzing
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VPN problems, are explained below:</p>
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<dl><dt class="dlterm">CFGOBJ (Configuration object)</dt>
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<dd>The name of the configuration object for which the trace is running. The
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object is either a line description, a network interface description, or a
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network server description.</dd>
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<dt class="dlterm">CFGTYPE (Configuration type)</dt>
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<dd>Whether a line (*LIN), a network interface (*NWI), or a network server
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(*NWS) is being traced.</dd>
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<dt class="dlterm">FMTTCP (Format TCP/IP data)</dt>
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<dd>Whether to format the trace for TCP/IP and UDP/IP data. Specify *YES to
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format the trace for IP data.</dd>
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<dt class="dlterm">TCPIPADR (Format TCP/IP data by address)</dt>
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<dd>This parameter consists of two elements. If you specify IP addresses on
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both elements, only IP traffic between those addresses will print.</dd>
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<dt class="dlterm">SLTPORT (IP port number)</dt>
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<dd>The IP port number to filter.</dd>
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<dt class="dlterm">FMTBCD (Format broadcast data)</dt>
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<dd>Whether all broadcast frames are printed. Yes is the default. If you do
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not want; for example, Address Resolution Protocol (ARP) requests, specify
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*NO; otherwise you may be overwhelmed with broadcast messages.</dd>
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</dl>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzajatroubleshootvpn.htm" title="Refer to this topic when you experience problems with your VPN connections.">Troubleshoot VPN</a></div>
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</div>
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<div class="reltasks"><strong>Related tasks</strong><br />
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<div><a href="rzajagetstartpd.htm" title="Vie this information to begin finding and correcting your VPN connection problems.">Get started with troubleshooting VPN</a></div>
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</div>
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</div>
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</body>
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