Computer Based Routers

Traditional, standalone routers are hardware specific: You purchase a specialized physical platform, including a chassis, sheet metal, power supply, CPU, memory, I/O ports, and a motherboard together with the routing engine. These components are described in "Routers and WANs."

In a standalone router, the routing engine is an integral part of the unit. It is not separable, nor portable, from the standalone router. In a computer-based router, the routing engine is executable software designed to run on a general-purpose computer rather than a highly specialized device. In fairness, this isn't a new trend. In fact, the earliest routers were really UNIX-based computers that calculated routes using one of the myriad primitive RIP-like protocols described in "Routing Information Protocol." This early form of software-based routing was, subsequently, almost completely supplanted by the various generations of hardware-based routers that emerged.

Figure 15-1 illustrates a typical, but now obsolete, configuration for using a computer-based router to calculate routes in the pre-PC era of computing.

Figure 15-1: An early computer-based router.



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In Figure 15-1, dumb terminals are hardwired to a UNIX server. This server, in addition to its application base, hosts a Routing Information Protocol (RIP) routing engine. This engine was the first generation of computer-based routing. It was used by the terminals and the server to access other internetworked devices.

The appearance of the specialized standalone routers brought some substantial benefits relative to computer-based routing:

• A processing platform dedicated to route calculation and packet forwarding

The Future of Routing

• Placement of the routing function at the boundary between the LAN and WAN rather than at the LAN's periphery

• Support for more advanced routing protocols

• Potential for sharing a WAN access facility across a greater base of users

• A more reliable platform that had fewer moving parts than an end system

These benefits resulted in the dominance of the standalone router. Over time, routers became increasingly more powerful and feature rich. These developments enabled standalone routers to expand their presence in internetworks. Specifically, they began to be used in nontraditional ways, such as to construct LAN backbones.

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