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+
+<head>
+<meta http-equiv="Content-Language" content="en-us">
+<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
+
+
+
+<title>Content</title>
+<base target="_self">
+</head>
+
+<body background="../../images/bg.gif" topmargin="0" leftmargin="0" marginheight="0" marginwidth="0" onLoad="window.focus();" link="#808080" vlink="#808080" alink="#808080">
+
+<table border="0" cellpadding="0" cellspacing="0" width="100%">
+ <tr>
+ <td bgcolor="#336666" width="18" valign="top">
+ <img border="0" src="../../images/content_lines.gif" width="16" height="25">
+ <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">
+ 1.1.7</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">Issues with NAT</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">
+ NAT has several advantages, including:
+ <img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12"></font><ul>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ NAT conserves the legally registered addressing scheme by allowing
+ the privatization of intranets. </font></li>
+ <li>
+
+ <font face="Arial" size="2">Increases the flexibility of connections
+ to the public network. Multiple pools, backup pools, and load
+ balancing pools can be implemented to assure reliable public network
+ connections. </font>
+ </li>
+ <li>
+
+ <font face="Arial" size="2">Consistency of the internal network
+ addressing scheme. On a network without private IP addresses and NAT,
+ changing public IP addresses requires the renumbering of all hosts on
+ the existing network. The costs of renumbering hosts can be
+ significant. NAT allows the existing scheme to remain while supporting
+ a new public addressing scheme. </font></li>
+ </ul>
+ <p>
+
+ <font FACE="Arial" SIZE="2">
+ NAT is not without drawbacks. Enabling address translation will cause
+ a loss of functionality, particularly with any protocol or application
+ that involves sending IP address information inside the IP payload.
+ This requires additional support by the NAT device.</font></p>
+ <p>
+
+ <font face="Arial" size="2">NAT increases delay. Switching path delays
+ are introduced because of the translation of each IP address within
+ the packet headers.</font></p>
+ <p>
+
+ <font face="Arial" size="2">Performance may be a consideration because
+ NAT is currently accomplished by using process switching. The CPU must
+ look at every packet to decide whether it has to translate it. The CPU
+ must alter the IP header, and possibly alter the TCP header.</font></p>
+ <p>
+
+ <font FACE="Arial" SIZE="2">
+ One significant disadvantage when implementing and using NAT is the
+ loss of end-to-end IP traceability. It becomes much more difficult to
+ trace packets that undergo numerous packet address changes over
+ multiple NAT hops. Hackers who want to determine the source of a
+ packet will find it difficult to trace or obtain the original source
+ or destination address. </font></p>
+ <p>
+
+ <font FACE="Arial" SIZE="2">
+ NAT also forces some applications that use IP addressing to stop
+ functioning because it hides end-to-end IP addresses. Applications
+ that use physical addresses instead of a qualified domain name will
+ not reach destinations that are translated across the NAT router.
+ Sometimes, this problem can be avoided by implementing static NAT
+ mappings. </font></p>
+ <p>
+
+ <font face="Arial" size="2">Cisco IOS NAT supports the following
+ traffic types:
+ <img border="0" src="../../images/2.gif" align="absmiddle" width="12" height="12"></font></p>
+ <ul>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ ICMP </font></li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ File Transfer Protocol (FTP), including PORT and PASV commands </font>
+ </li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ NetBIOS over TCP/IP, datagram, name, and session services </font>
+ </li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ RealNetworks' RealAudio </font></li>
+ <li>
+
+ <font face="Arial" size="2">White Pines' CUSeeMe </font></li>
+ <li>
+
+ <font face="Arial" size="2">Xing Technologies' StreamWorks </font></li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ DNS "A" and "PTR" queries </font></li>
+ <li>
+
+ <font face="Arial" size="2">H.323/Microsoft NetMeeting, IOS versions
+ 12.0(1)/12.0(1)T and later </font></li>
+ <li>
+
+ <font face="Arial" size="2">VDOnet's VDOLive, IOS versions
+ 11.3(4)11.3(4)T and later </font></li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ VXtreme's Web Theater, IOS versions 11.3(4)11.3(4)T and later </font></li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ IP Multicast, IOS version 12.0(1)T with source address translation
+ only </font>
+ </li>
+ </ul>
+ <p>
+
+ <font FACE="Arial" SIZE="2">
+ Cisco IOS NAT does not support the following traffic types:</font></p>
+ <ul>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ Routing table updates </font></li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ DNS zone transfers </font></li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ BOOTP </font></li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ talk and ntalk protocols </font></li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ Simple Network Management Protocol (SNMP)</font></li>
+ </ul>
+ <p>
+ <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>
+ </TABLE>
+
+ <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">
+ <a href="javascript:void(0)" onClick="window.open('../../activities/ch01/activity_1_1_7.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/media_icon.gif" width="25" height="25"></a> <b>
+ <a onClick="window.open('../../activities/ch01/activity_1_1_7.html','Interactivity','width=740,height=390,toolbar=0,resizable=yes,scrollbars=0,screenX=26,screenY=38,left=26,top=38');" href="javascript:void(0)">Interactive Media Activity</a></b></font></p>
+ </font><font FACE="Arial" SIZE="2" COLOR="#808080">
+ <p>Checkbox: Issues with NAT</p>
+ <p>When the student has completed this activity, the student
+ will be able to identify issues with the use of NAT.</p>
+ </font><font FACE="Arial" SIZE="2" COLOR="#000000">
+ <p><IMG alt="" height="2" width="1" src="../../images/s.gif"></p></TD>
+ </TR>
+ </TABLE>
+ </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>
+ </TABLE>
+
+ <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/</a><br>
+ <a target="_blank" href="http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080094c32.shtml">
+ tk648/tk361/technologies_tech_note</a><br>
+ <a target="_blank" href="http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080094c32.shtml">
+ 09186a0080094c32.shtml</a></font></p>
+
+ <p>
+ <IMG alt="" height="2" width="1" src="../../images/s.gif"></p>
+ </TD>
+ </TR>
+ </TABLE>
+ </TD>
+ </TR>
+ </TABLE>
+ </TD>
+ </TR>
+ </TABLE><p>
+
+ </td>
+ </tr>
+ </table>
+
+</body>
+
+</html>
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