The subject of security never strays far from the minds of IT workers, for good reason. If there is a network with even just one connection to another network, it needs to be secured. RADIUS, or Remote Authentication Dial-In User Service, is a widely deployed protocol that enables companies to authenticate, authorize and account for remote users who want access to a system or service from a central network server. Originally developed for dial-up remote access, RADIUS is now used by virtual private network (VPN) servers, wireless access points, authenticating Ethernet switches, Digital Subscriber Line (DSL) access, and other network access types. Extensible, easy to implement, supported, and actively developed, RADIUS is currently the de facto standard for remote authentication.

RADIUS provides a complete, detailed guide to the underpinnings of the RADIUS protocol, with particular emphasis on the utility of user accounting. Author Jonathan Hassell draws from his extensive experience in Internet service provider operations to bring practical suggestions and advice for implementing RADIUS. He also provides instructions for using an open-source variation called FreeRADIUS.

"RADIUS is an extensible protocol that enjoys the support of a wide range of vendors," says Jonathan Hassell. "Coupled with the amazing efforts of the open source development community to extend RADIUS's capabilities to other applications-Web, calling card security, physical device security, such as RSA's SecureID-RADIUS is possibly the best protocol with which to ensure only the people that need access to a resource indeed gain that access."

This unique book covers RADIUS completely, from the history and theory of the architecture around which it was designed, to how the protocol and its ancillaries function on a day-to-day basis, to implementing RADIUS-based security in a variety of corporate and service provider environments. If you are an ISP owner or administrator, corporate IT professional responsible for maintaining mobile user connectivity, or a web presence provider responsible for providing multiple communications resources, you'll want this book to help you master this widely implemented but little understood protocol.

Our look is the result of reader comments, our own experimentation, and feedback from distribution channels. Distinctive covers complement our distinctive approach to technical topics, breathing personality and life into potentially dry subjects. The animal on the cover of RADIUS is a Dolium shell. This shell is that of Orcula Dolium, one of a small family of snails. Dolium live in leaf litter or on mossy rocks on mountains such as the Alps and the Carpathians. Their shells are cylindrical, and they have rounded mouths and teeth. Their color varies from yellowish to reddish brown. Darren Kelly was the production editor and Maureen Dempsey was the copyeditor for RADIUS. Octal Publishing, Inc. provided production services and wrote the index. Sheryl Avruch and Claire Cloutier provided quality control. Interior composition was done by Philip Dangler and Derek Di Matteo.

Hanna Dyer designed the cover of this book, based on a series design by Edie Freedman. The cover image is a 19th-century engraving from the Dover Pictorial Archive. Emma Colby produced the cover layout with QuarkXPress 4.1 using Adobe's ITC Garamond font.

David Futato designed the interior layout. This book was converted to FrameMaker 5.5.6 with a format conversion tool created by Erik Ray, Jason McIntosh, Neil Walls, and Mike Sierra that uses Perl and XMLtechnologies. The text font is Linotype Birka; the heading font is Adobe Myriad Condensed; and the code font is Lucas-Font's TheSans Mono Condensed. The illustrations that appear in the book were produced by Robert Romano and Jessamyn Read using Macromedia FreeHand 9 and Adobe Photoshop 6. The tip and warning icons were drawn by Christopher Bing. This colophon was written by Linley Dolby.