Chapter 6. Routing with Linux

6.0. Introduction

Linux on ordinary commodity hardware can handle small to medium routing needs just fine. The low- to mid-range commercial routers use hardware comparable to ordinary PC hardware. The main difference is form factor and firmware. Routers that use a real-time operating system, like the Cisco IOS, perform a bit better under heavy loads than Linux-based routers. Big companies with large, complex routing tables and ISPs need the heavy-duty gear. The rest of us can get by on the cheap just fine. You don’t want poor-quality hardware; that’s always a bad idea. You just don’t need to spend the moon for simple routing like this chapter covers.

The highest-end routers use specialized hardware that is designed to move the maximum number of packets per second. They come with multiple fat data buses, multiple CPUs, and Ternary Content Addressable Memory (TCAM) memory. TCAM is several times faster than the fastest system RAM, and many times more expensive. TCAM is not used in lower-cost devices, and no software can shovel packets as fast as TCAM.

But, for the majority of admins, this is not an issue because you have an ISP to do the heavy lifting. Your routing tables are small because you’re managing only a few networks that are directly under your care.

In this chapter, we’re going to perform feats of static routing using the route and ip commands, and dynamic routing using two interior routing protocols, Routing Information Protocol (RIP) and Open Shortest ...

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