78 lines
5.7 KiB
HTML
78 lines
5.7 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<meta name="DC.Title" content="L2TP (tunneling) support for PPP connections" />
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<meta name="abstract" content="Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol that extends PPP to support a link layer tunnel between a requesting L2TP client (L2TP Access Concentrator or LAC) and a target L2TP server endpoint (L2TP Network Server or LNS)." />
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<meta name="description" content="Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol that extends PPP to support a link layer tunnel between a requesting L2TP client (L2TP Access Concentrator or LAC) and a target L2TP server endpoint (L2TP Network Server or LNS)." />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<title>L2TP (tunneling) support for PPP connections</title>
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</head>
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<body id="rzaiyl2tpsupport"><a name="rzaiyl2tpsupport"><!-- --></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">L2TP (tunneling) support for PPP connections</h1>
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<div><p>Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol that
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extends PPP to support a link layer tunnel between a requesting L2TP client
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(L2TP Access Concentrator or LAC) and a target L2TP server endpoint (L2TP
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Network Server or LNS).</p>
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<div class="section"><h4 class="sectiontitle">Layer 2 Tunneling Protocol</h4><p>By using Layer 2 Tunneling
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Protocol (L2TP) tunnels, it is possible to separate the location at which
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the dial-up protocol ends and where the access to the network is provided.
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That is why L2TP is also referred to as <dfn class="term">Virtual PPP</dfn>.</p>
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<p>An
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Internet Service Provider (ISP) uses the virtual line mode to operate virtual
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private networks (VPN). See <a href="../rzaja/rzajaremoteuser.htm">Configure an L2TP connection protected by VPN</a> for
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a better understanding of how IPSec works with L2TP.</p>
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<div class="p">These figures illustrate
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three different tunneling implementations of L2TP.<div class="fignone"><span class="figcap">Figure 1. PPP virtual
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initiator or PPP virtual terminator</span><br /><img src="rbaee563.gif" alt="L2TP: PPP Virtual Initiator or PPP Virtual Terminator" /><br /></div>
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<div class="fignone"><span class="figcap">Figure 2. PPP dial initiator or PPP virtual terminator</span><br /><img src="rbaee561.gif" alt="L2TP: PPP Dial Initiator or PPP Virtual Terminator" /><br /></div>
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<div class="fignone"><span class="figcap">Figure 3. PPP virtual dial or PPP virtual answer</span><br /><img src="rbaee562.gif" alt="L2TP: PPP Virtual Dial or PPP Virtual Answer" /><br /></div>
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</div>
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</div>
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<div class="section"><p>The L2TP protocol is documented as a Request For Comment standard,
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RFC2661. More information about RFCs can be found on the <a href="http://www.rfc-editor.org" target="_blank">RFC Editor</a> Web page.
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An L2TP tunnel can extend across an entire PPP session or only across one
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segment of a two-segment session. This can be represented by four different
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tunneling models: </p>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="rzaiyvoltunnel.htm">Voluntary tunnel</a></strong><br />
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In the voluntary tunnel model, a tunnel is created by the user, typically by the use of an L2TP-enabled client.</li>
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<li class="ulchildlink"><strong><a href="rzaiycomptic.htm">Compulsory tunnel model - incoming call</a></strong><br />
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In the compulsory tunnel model - incoming call, a tunnel is created without any action from the user and without allowing the user any choice.</li>
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<li class="ulchildlink"><strong><a href="rzaiycomptrd.htm">Compulsory tunnel model - remote dial</a></strong><br />
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In the compulsory tunnel model - remote dial, the home gateway (LNS) initiates a tunnel to an ISP (LAC) and instructs the ISP to place a local call to the PPP answer client.</li>
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<li class="ulchildlink"><strong><a href="rzaiymultihop.htm">L2TP multi-hop connection</a></strong><br />
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An L2TP multi-hop connection is a way of redirecting L2TP traffic on behalf of client LACs and LNSs.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaiyconnalts.htm" title="PPP can transmit datagrams over serial point-to-point links.">Connection alternatives</a></div>
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</div>
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</div>
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</body>
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</html>
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