Linux Routers

Sitting at your average Linux box is becoming simpler by the day, but the complexity and volume of information that that machine is likely to transmit and recieve is only getting greater. Reader Martin Barry contributed this review of Linux Routers. This book promises to unravel that complexity for the reader willing to trade some time and effort for a custom solution to their own routing requirements.

Linux Routers author Tony Mancill pages 329 publisher Prentice Hall rating 7 reviewer Martin Barry ISBN 0-13-086113-8 summary Fundamental look at replacing brand name routers with ones based on generic hardware and Linux. Develops concepts of core routing features and relevant extensions in the context of six router applications including LAN, WAN and Internet.

Overview Linux Routers is an interesting little book that pulls together the kind of information that one could find browsing various HOW-TOs and guides into a concise narrative explaining the tasks required to build and operate Linux-based routers.

Opening the book is a discussion on the fundamental theories underlying routing and the infrastruture required to implement routing solutions. For those (like myself) who have little exposure to network administration this will be particulary helpful as a lead in to the following chapters.

There is a chapter to further build on the basics of IP (addresses including RFC1918, subnetting, routing tables), ethernet (MAC addresses, ARP, switching) and wide area networks (types of links, integrating with telco hardware, billing).

The detail increases as the book progresses. It starts with the simplest installation, routing between two ethernet segments covering the basics of setting up Linux networking and routing. Methods of IP accounting are also introduced. Mention is also made of the Linux Router Project and the single floppy distribution they have developed.

Moving onto WAN routers introduces the telco issues and ways to preserve bandwdith (http proxy, caching dns). IPchains is introduced in the context of masquerading otherwise unroutable addresses. Various tools are listed in a section that demonstrates how to view traffic on the network for educational and debugging purposes. Monitoring of traffic over a router is also described, using MRTG to collect and beautify data. Chapter 7 includes methods of reducing said traffic such as http caches and a DNS slave at the remote site.

A border router to the Internet is used to raise related security issues and the use of proxy servers to screen access from the outside in or the inside out. This information bridges across chapters 6 and 8 and includes topics like packet filtering firewalls, port redirection and proxies. The flexibility of Linux is demonstrated by the ability to integrate routing and Internet servers on a single box. With obvious reservations about how wise that is, it is pertinent that failure detection, notification and recovery are all covered.

What's to like The information starts out simple and builds on itself in cyclical nature as the book progresses. The six scenarios are the ones likely to be encountered in a production environment and illustrate the benefits of using Linux routers.

The issues of choosing Linux as a router are well addressed, including discussions on thorny topics like "Total Cost of Ownership," and provide a framework for you to assess your own situation. The writer's style is clear and easy to read.

Different WAN and Internet telco links are discussed (POTS, frame relay, dedicated digital access circuit) including how to configure the link and what protocols to run over it.

Peripheral issues, such as troubleshooting tcp or proxy servers, are dealt with well. Information is provided to allow you to understand the integration with the routing infrastructure you are deploying. When the topic starts to drift from the task at hand the author makes good use of redirecting people interested in more detail to other references (Web sites, books).

What's annoying The author is a part of the Debian project so some things have a bit of a Debian slant on them (this includes the file system layout referred to and the config files). This shouldn't be too much of an issue for most people, though it will require a thorough understanding of one's own system or problem-solving via your distribution's manual. WAN hardware and software discussions are limited by the author's experience, with a particular brand of card and one software package (wanpipe -- of which the author is the Debian maintainer) being focused on.

Alternatives are mentioned, but not in great depth, and the examples therefore might not be portable to your choice of card or software.

Summary If you are comfortable with enabling routing, IPchains, proxy servers and troubleshooting tcp/ip on Linux, this book will be of little use other than to provide a step-by-step approach. On the other hand, if you currently use brand-name routers but have sometimes wondered whether that 486 in the corner could be put to good use, this book will certainly guide you on your travels.

Table of Contents Note: the author uses the elements to name boxen, hence the names of the chapters.

1. Routing Building Blocks (Hardware, Environment, Software)
2. IP, Ethernet and Telephony Basics (Routing, Ethernet, WAN)
3. Silicon - LAN Router (LAN Routing, IP Aliasing and Accounting)
4. Erbium - an Extranet Router (IP Masq, IP Monitoring)
5. Zinc - Frame Relay Router (WAN Hardware and Software, MRTG)
6. Oxygen - Internet Router (Security, Firewalling, Failure Detection)
7. Californium - Satellite Office Router (Caches and Slaves, Multifunction Routers, Remote System Support)
8. Hafnium - Internet Services Router (Proxying, IP Redirection, Routing Daemons, Emergency Recovery)

Appendices

• A) Links
• B) Compiling a Kernel
• C) Testing Strategies
• D) Ethics and Other Considerations
• E) GPL

You can purchase this book from ThinkGeek.