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Network Security Hacks by Andrew Lockhart

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Create a Cross-Platform VPN

Use OpenVPN to easily tie your networks together.

Creating a VPN can be quite difficult, especially when dealing with clients using multiple platforms. Quite often, a single VPN implementation isn’t available for all of them. As an administrator, you can be left with trying to get different VPN implementations to operate on all the different platforms that you need to support, which can become a nightmare.

Luckily, someone has stepped in to fill the void in cross-platform VPN packages and has written OpenVPN (http://openvpn.sourceforge.net). It supports Linux, Solaris, OpenBSD, FreeBSD, NetBSD, Mac OS X, and Windows 2000/XP. OpenVPN achieves this by implementing all of the encryption, key-management, and connection-setup functionality in a user-space daemon, leaving the actual tunneling portion of the job to the host operating system.

To accomplish the tunneling, OpenVPN makes use of the host operating system’s virtual TUN or TAP device. These devices export a virtual network interface, which is then managed by the openvpn process to provide a point-to-point interface between the hosts participating in the VPN. Instead of traffic being sent and received on these devices, it’s sent and received from a user-space program. Thus, when data is sent across the virtual device, it is relayed to the openvpn program, which then encrypts it and sends it to the openvpn process running on the remote end of the VPN link. When the data is received on the other end, ...

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