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Troubleshooting Virtual Private Networks by Mark Lewis

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Chapter 4. Troubleshooting the Layer 2 Tunneling Protocol Version 2 VPNs

Layer Two Tunneling Protocol (L2TP) version 2 is defined in RFC 2661 and combines the best features of Layer Two Forwarding (L2F) and Point-to-Point Tunneling Protocol (PPTP). L2TP, like L2F and PPTP, is designed to separate the functionality of the traditional Network Access Server (NAS). Calls from remote access clients are terminated at a local access concentrator known as the L2TP Access Concentrator (LAC), but PPP connections are terminated on a separate device called an L2TP Network Server (LNS). PPP connections are tunneled from the LAC to the LNS over an intervening network.

This separation of traditional NAS functionality can potentially lead to cost savings because ...

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