A virtual private network (VPN) enables computers to access remote resources--like the mail store on another office's mail server--from a geographically remote location. Rather than access the files over a private (and expensive) wide area network (WAN) link, however, a VPN makes its data transmissions across the open Internet. The magic is in making the communications secure, a critical job that requires a tunneling protocol that implements encryption. Building Linux Virtual Private Networks
shows you how to set up VPNs without spending a lot of money, and without compromising ease of use or security. Oleg Kolesnikov and Brian Hatch emphasize network-to-network connectivity--fixed links between sites--rather than network-to-client connections. They show you how to use Linux to build a secure system of permanent--yet virtual--data links. There's coverage, for example, of the PoPToP daemon for handling Point-to-Point Tunneling Protocol (PPTP), but there's no coverage of non-Linux clients with which to connect it.
There's a nice balance of managerial information (useful for justifying a VPN, and a Linux one in particular, to your boss) and technical details in these pages. Each of the covered packages gets nice documentation, complete with listings of configuration files and explicit statements of console input and output. --David Wall
Topics covered: Packages designed to enable VPNs between Linux gateways. Software oriented toward standard protocols (PPP-over-SSH, PPP-over-SSL, IPsec, and PPTP) as well as nonstandard ones (VTun, cIPe, and tinc). Lots of coverage goes to FreeS/WAN and ppp-mppe.