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<img border="0" src="../../images/transdot.gif" width="2" height="1"></td>
<td bgcolor="#336666"><font face="Arial" size="2" color="#FFFFFF"><b>1.1</b></font></td>
<td bgcolor="#336666"><img border="0" src="../../images/transdot.gif" width="10" height="1"></td>
<td bgcolor="#336666" width="100%">
<b><font face="Arial" size="2" color="#FFFFFF">Scaling Networks with NAT
and PAT</font></b></td>
<td width="9" bgcolor="#336666"> </td>
</tr>
<tr>
<td bgcolor="#669999" height="25" width="18"> </td>
<td bgcolor="#669999" height="25"><b><font face="Arial" size="2" color="#FFFFFF">
1.1.6</font></b></td>
<td bgcolor="#669999"><img border="0" src="../../images/transdot.gif" width="10" height="1"></td>
<td bgcolor="#669999" height="25" width="100%"><b>
<font face="Arial" size="2" color="#FFFFFF">Troubleshooting NAT and PAT
configuration</font></b></td>
<td bgcolor="#669999" height="25" width="9"> </td>
</tr></table>
<table border="0" cellpadding="0" cellspacing="0" width="95%" bordercolor="#111111">
<tr>
<td width="15"></td>
<td>
<font FACE="Arial" SIZE="2">
When IP connectivity problems in a NAT environment exist, it is often
difficult to determine the cause of the problem. Many times NAT is
mistakenly blamed, when in reality there is an underlying problem.</font><p>
<font FACE="Arial" SIZE="2">
When trying to determine the cause of an IP connectivity problem, it
helps to rule out NAT. Use the following steps to determine whether
NAT is operating as expected:</p>
<ol>
<li>Based on the configuration, clearly define what NAT is supposed
to achieve.</li>
<li>Verify that correct translations exist in the translation table. </li>
<li>Verify the translation is occurring by using </font>
<font FACE="Courier New" SIZE="2">
<b>show</b></font><font FACE="Arial" SIZE="2">
and </font>
<font FACE="Courier New" SIZE="2">
<b>debug</b></font><font FACE="Arial" SIZE="2">
commands. </li>
<li>Review in detail what is happening to the packet and verify that
routers have the correct routing information to move the packet
along.</font></li>
</ol>
<p>
<font FACE="Arial" SIZE="2">
Use the </font>
<font FACE="Courier New" SIZE="2">
<b>debug ip nat</b></font><font FACE="Arial" SIZE="2">
command to verify the operation of the NAT
feature by displaying information about every packet that is
translated by the router. The </font><font FACE="Courier New" SIZE="2"><b>debug ip nat
<i>detailed</i></b></font><font FACE="Arial" SIZE="2">
command generates
a description of each packet considered for translation. This command
also outputs information about certain errors or exception conditions,
such as the failure to allocate a global address.</font></p>
<p>
<font FACE="Arial" SIZE="2">
Figure <img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12"> shows
a sample
</font>
<font FACE="Courier New" SIZE="2">
<b>debug ip nat</b></font><font FACE="Arial" SIZE="2">
output. In this example, the
first two lines of the debugging output show that a Domain Name System
(DNS) request and reply were produced. The remaining lines show the
debugging output of a Telnet connection from a host on the inside of
the network to a host on the outside of the network.
</font>
</p>
<p>
<font FACE="Arial" SIZE="2">
Decode the
</font>
<font FACE="Courier New" SIZE="2">
<b>debug</b></font><font FACE="Arial" SIZE="2">
output by using the following key points:
</font>
</p>
<ul>
<li>
<font FACE="Arial" SIZE="2">
The asterisk next to NAT indicates that the translation is occurring
in the fast-switched path. The first packet in a conversation will
always go through the slow path, which means this first packet is
process-switched. The remaining packets will go through the
fast-switched path if a cache entry exists.
</font>
</li>
<li>
<font FACE="Arial" SIZE="2">
s = a.b.c.d<b> </b> is the source address.
</font>
</li>
<li>
<font face="Arial" size="2">Source address a.b.c.d is translated to
w.x.y.z. </font>
</li>
<li>
<font face="Arial" size="2">d = e.f.g.h is the destination address.
</font>
</li>
<li>
<font FACE="Arial" SIZE="2">
The value in brackets is the IP identification number. This
information may be useful for debugging. This is useful, for
example, because it enables correlation with other packet traces
from protocol analyzers.
</font>
</li>
</ul>
<p>
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<TR>
<TD valign="top">
<TABLE bgcolor="#669999" width="100%" cellspacing="0" cellpadding="0" border="0">
<TR>
<TD width="5">
<img border="0" src="../../images/lab_toplft.gif" width="116" height="23"></TD>
<TD>
<IMG alt="" height="1" width="3" src="../../images/s.gif"></TD><TD align="right" valign="top">
<IMG alt="" src="../../images/corner_ur_7.gif" width="7" height="7"></TD>
</TR>
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<TR>
<TD>
<TABLE width="100%" cellpadding="2" cellspacing="0" border="0" bordercolor="#111111">
<TR>
<TD bgcolor="#ffffff" width="15"> </TD>
<TD bgcolor="#ffffff"><font FACE="Arial" SIZE="2" COLOR="#000000">
<p><font color="#808080">
<a target="main" href="../lab1_1_6/index.html">
<img border="0" src="../../images/lab_icon.gif" width="25" height="25"> <b>
Lab Activity</b></a></font></p>
</font><font FACE="Arial" SIZE="2" COLOR="#808080">
<p>Lab Exercise: Troubleshooting NAT and PAT</p>
</font><font FACE="Arial" SIZE="2" COLOR="#000000">
<p><font color="#808080">In this lab, the student will configure
a router for Network Address Translation (NAT) and Port Address
Translation (PAT). </font></p>
<p></TD>
</TR>
</TABLE>
</TD>
</TR>
</TABLE>
</TD>
</TR>
</TABLE>
<TABLE bgcolor="#669999" width="95%" cellspacing="0" cellpadding="0" border="0">
<TR>
<TD width="5">
<img border="0" src="../../images/lab_toplft.gif" width="116" height="23"></TD>
<TD>
<IMG alt="" height="1" width="3" src="../../images/s.gif"></TD><TD align="right" valign="top">
<IMG alt="" src="../../images/corner_ur_7.gif" width="7" height="7"></TD>
</TR>
</TABLE>
<TABLE bgcolor="#B0AFAF" width="95%" cellspacing="0" cellpadding="0" border="0">
<TR>
<TD>
<TABLE width="100%" cellpadding="2" cellspacing="0" border="0" bordercolor="#111111">
<TR>
<TD bgcolor="#ffffff" width="15"> </TD>
<TD bgcolor="#ffffff"><font FACE="Arial" SIZE="2" COLOR="#000000">
<p><font color="#808080">
<a href="javascript:void(0)" onClick="window.open('../../elabs/mod01/elab_1_1_6/elab1_1_6.html','Interactivity','width=740,height=390,toolbar=0,resizable=yes,scrollbars=0,screenX=26,screenY=38,left=26,top=38');">
<img border="0" src="../../images/lab_icon.gif" width="25" height="25"><b></a>
<a href="javascript:void(0)" onClick="window.open('../../elabs/mod01/elab_1_1_6/elab1_1_6.html','Interactivity','width=740,height=390,toolbar=0,resizable=yes,scrollbars=0,screenX=26,screenY=38,left=26,top=38');">Lab Activity</a></b></font></p>
</font><font FACE="Arial" SIZE="2" COLOR="#808080">
<p>e-Lab Activity: Troubleshooting NAT and PAT</p>
</font><font FACE="Arial" SIZE="2" COLOR="#000000">
<p><font color="#808080">In this lab, the student will configure
a router for Network Address Translation and Port Address
Translation.</font></p>
<p></TD>
</TR>
</TABLE>
</TD>
</TR>
</TABLE>
<TABLE bgcolor="#B0AFAF" width="95%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top">
<TABLE bgcolor="#669999" width="100%" cellspacing="0" cellpadding="0" border="0">
<TR>
<TD width="5">
<img border="0" src="../../images/lab_toplft.gif" width="116" height="23"></TD>
<TD><IMG alt="" height="1" width="3" src="../../images/s.gif"></TD><TD align="right" valign="top">
<IMG alt="" src="../../images/corner_ur_7.gif" width="7" height="7"></TD>
</TR>
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<TABLE bgcolor="#B0AFAF" width="100%" cellspacing="0" cellpadding="0" border="0">
<TR>
<TD>
<TABLE width="100%" cellpadding="2" cellspacing="0" border="0" bordercolor="#111111">
<TR>
<TD bgcolor="#ffffff" width="15"> </TD>
<TD bgcolor="#ffffff"><font FACE="Arial" SIZE="2" COLOR="#000000">
<p><font color="#808080">
<img border="0" src="../../images/links_icon.gif" width="25" height="25">
<b>Web Links</b></font></p>
</font><font FACE="Arial" SIZE="2" COLOR="#808080">
<p>Verifying NAT Operation and Basic NAT Troubleshooting<p>
<a target="_blank" href="http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080094c32.shtml">
http://www.cisco.com/en/US/tech/
tk648/tk361/technologies_tech_ note09186a0080094c32.shtml</a></font></p>
<p>
<IMG alt="" height="2" width="1" src="../../images/s.gif"></p>
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