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<td bgcolor="#336666"><b><font face="Arial" size="2" color="#FFFFFF">3.2</font></b></td>
<td bgcolor="#336666"><img border="0" src="../../images/transdot.gif" width="10" height="1"></td>
<td bgcolor="#336666" width="100%"><strong>
<font face="Arial" size="2" color="#FFFFFF">PPP Authentication</font></strong></td>
<td width="9" bgcolor="#336666"> </td>
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<tr>
<td bgcolor="#669999" height="25" width="18"> </td>
<td bgcolor="#669999" height="25"><b>
<font face="Arial" size="2" color="#FFFFFF">3.2.2</font></b></td>
<td bgcolor="#669999"><img border="0" src="../../images/transdot.gif" width="10" height="1"></td>
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<font size="2" color="#FFFFFF"><b><span style="font-family: Arial">
Establishing a PPP session</span></b></font></td>
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<font size="2" face="Arial">
PPP session establishment progresses through three
phases. These phases are link establishment, authentication, and the
network layer protocol phase.
<img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12"> LCP frames are used to accomplish the
work of each of the LCP phases. The following three classes of LCP
frames are used in a PPP session:</font><ul>
<li>
<font size="2" face="Arial">
Link-establishment frames are used to establish and configure a
link.</font></li>
<li>
<font size="2" face="Arial">
Link-termination frames are used to terminate a link. </font></li>
<li>
<font size="2" face="Arial">
Link-maintenance frames are used to manage and debug a link.</font></li>
</ul>
<p>
<font size="2" face="Arial">
The three PPP session establishment phases are:</font></p>
<ul>
<li>
<font size="2" face="Arial">
<b>Link-establishment phase</b> � In this phase each PPP device sends LCP
frames to configure and test the data link. LCP frames contain a
configuration option field that allows devices to negotiate the use of
options such as the maximum transmission unit (MTU), compression of
certain PPP fields, and the link-authentication protocol. If a
configuration option is not included in an LCP packet, the default
value for that configuration option is assumed.
<img border="0" src="../../images/2.gif" align="absmiddle" width="12" height="12"> Before any network
layer packets can be exchanged, LCP must first open the connection and
negotiate the configuration parameters. This phase is complete when a
configuration acknowledgment frame has been sent and received.</font></li>
<li>
<font size="2" face="Arial">
<b>Authentication phase (optional)</b> � After the link has been established
and the authentication protocol decided on, the peer may be
authenticated. Authentication, if used, takes place before the network
layer protocol phase is entered. As part of this phase, LCP also
allows for an optional link-quality determination test. The link is
tested to determine whether the link quality is good enough to bring
up network layer protocols.
<img border="0" src="../../images/3.gif" align="absmiddle" width="12" height="12">
<img border="0" src="../../images/4.gif" align="absmiddle" width="12" height="12"></font></li>
<li>
<font size="2" face="Arial">
<b>Network layer protocol phase</b> � In this phase the PPP devices send NCP
packets to choose and configure one or more network layer protocols,
such as IP.
<img border="0" src="../../images/5.gif" align="absmiddle" width="12" height="12"> Once each of the chosen network layer protocols has been
configured, packets from each network layer protocol can be sent over
the link. If LCP closes the link, it informs the network layer
protocols so that they can take appropriate action. The </font>
<font size="2" face="Courier New">
<b>show interfaces</b></font><font size="2" face="Arial"> command
reveals the LCP and NCP states under PPP configuration.</font></li>
</ul>
<p>
<font size="2" face="Arial">
The PPP link remains configured for communications until LCP or NCP
frames close the link or until an inactivity timer expires or a user
intervenes.</font></p>
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<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>
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<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/ch03/activity_3_2_2.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/ch03/activity_3_2_2.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>Drag and Drop: Establishing a PPP Session</p>
<p>When the student has completed this activity, the student
will know the three steps in establishing a PPP Session.</p>
</font><font FACE="Arial" SIZE="2" COLOR="#000000">
<p><IMG alt="" height="2" width="1" src="../../images/s.gif"></p></TD>
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<TD>
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<p><font color="#808080">
<a href="javascript:void(0)" onClick="window.open('../../elabs/mod03/elab_3_2_2/elab3_2_2.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/mod03/elab_3_2_2/elab3_2_2.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: show interfaces</p>
<p>In this activity, the student will demonstrate how to use the
</font><font FACE="Courier New" SIZE="2" COLOR="#808080">
<b>show interfaces</b></font><font FACE="Arial" SIZE="2" COLOR="#808080">
command to display statistics for interfaces configured on the
router for access server.</p>
</font><font FACE="Arial" SIZE="2" COLOR="#000000">
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