Virtual Private Networks

Preface

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Definition

A regular phyiscally existing network consisting of cables and routers/switches/etc is called a network. You run the various known internet protocols layer 1-4 on it. You can also use those protocols to emulate a virtual network. This is mostly done in layer 2 (IP). You tunnel the data of the virtual network encapsulated in IP-Packets for example. If you secure your tunnel as well with various encryption methods one might call the tunneled data a virtual private network. This is used in various scenarios, mostly for tunneling sensitive information over an inherently insecure architecture - for example to connect two corporate LANs over the internet.

Implementation

PPTP (Microsoft)

Preface

How does it work?

Authentication

Encryption

Implementation Unix

mppe-patch

pptpd

Clients

MacOS

Mac OS X supports VPN-Connections out the box since 10.3. Included are Clients for PPTP and L2TP over IPSec. Unfortunately, not all of the major open source clients seems to have been ported to this platform. But the 10.3+ Clients are well integrated into the OS and provide a basic level functionality that should be sufficient.