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Layer 2 Forwarding Protocol
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<h2 id="use">Use</h2> <p>Virtual dial-up allows many separate and autonomous protocol domains to share common access infrastructure including modems, Access Servers, and ISDN routers. <a href="/facts/Request_for_Comments/esftTvE7">RFCs</a> prior to 2341 have specified protocols for supporting IP dial-up via <a href="/facts/Serial_Line_Internet_Protocol/oqUaoA0f">SLIP</a> and multiprotocol dial-up via <a href="/facts/Point-to-Point_Protocol/XLaU6D71">PPP</a>. </p> <h2 id="l2f-packet-structure">L2F packet structure</h2> <table><tbody><tr><th colspan="13">Bits 0-12</th><th colspan="3">13-15</th><th colspan="8">16-23</th><th colspan="8">24-31</th></tr><tr><td colspan="1">F</td><td colspan="1">K</td><td colspan="1">P</td><td colspan="1">S</td><td colspan="1">0</td><td colspan="1">0</td><td colspan="1">0</td><td colspan="1">0</td><td colspan="1">0</td><td colspan="1">0</td><td colspan="1">0</td><td colspan="1">0</td><td colspan="1">C</td><td colspan="3">Ver</td><td colspan="8">Protocol</td><td colspan="8">Sequence (opt)</td></tr><tr><td colspan="16">Multiplex ID</td><td colspan="16">Client ID</td></tr><tr><td colspan="16">Length</td><td colspan="16">Payload offset (opt)</td></tr><tr><td colspan="32">Packet key (optional)</td></tr><tr><td colspan="32">Payload</td></tr><tr><td colspan="16"> </td><td colspan="16">L2F Checksum (opt)</td></tr></tbody></table> <h2 id="other-vpn-protocols">Other VPN protocols</h2> <ul><li><a href="/facts/IPsec/01MwcET1">IPsec</a></li> <li>L2TP <a href="/facts/Layer_2_Tunneling_Protocol/50sRGptx">Layer 2 Tunneling Protocol</a></li> <li>PPTP <a href="/facts/Point-to-Point_Tunneling_Protocol/jYb3uG0Y">Point-to-Point Tunneling Protocol</a></li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="http://www.cisco.com/warp/public/732/L2F/">L2F on Cisco.com</a></li> <li><a href="http://www.cisco.com/en/US/tech/tk801/tk703/tsd_technology_support_protocol_home.html">VPDN on Cisco.com</a></li> <li><a href="http://www.cisco.com/en/US/tech/tk827/tk369/tk388/tsd_technology_support_sub-protocol_home.html">L2TP on Cisco.com</a></li> <li><a href="http://tools.ietf.org/html/rfc2341">RFC2341 on IETF.org</a></li> <li><a href="http://www.rfc-archive.org/getrfc.php?rfc=2341">RFC2341 on RFC Archive</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>RFC2341 on IETF.org <a href="http://tools.ietf.org/html/rfc2341" target="_blank">http://tools.ietf.org/html/rfc2341</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> </ol>