To say that Cisco Systems Inc. has a few products is like saying McDonalds sells a few hamburgers. Since 1984, Cisco has improved their original routers, enhancing features both in hardware and operating system software, mounting success upon success. Most of the "big iron" (that’s industry-speak for large expensive pieces of equipment) Cisco sells will only seen by a few highly trained network engineers. Folks who are full-time, part-time, and accidental network administrators will most likely only see only Cisco’s smaller offerings.
These smaller products have become commodities since the advent of the Internet (it’s that World Wide Web thing, and if you don’t know about it by now, I’m certainly not going to let you in on the secret). Routers used to be specialty items, seldom seen, and only sold as part of communications packages by network design and troubleshooting companies, or large telephone companies. Now every mom and pop ISP (Internet Service Provider), two-bit consultant, and mail order catalog has routers, hubs, cabling, and other hard core data communications gear available. All you need is a credit card, and a Cisco router can be at your door in a few short hours, sooner if you’re in a major metropolitan area.
We will focus on a small cross section of Cisco routers, primarily, those available as commodity products and the series just above them. This will provide a broad overview of what products are available and suggest how to use them. Most of the commodity routers come in fixed configurations, although each router series will have several variants available. The newer and higher end routers are available in modular configurations. These tend to be more expensive though extremely flexible and much harder to configure. Additionally, you will need to understand what external, non-Cisco products are required to make them talk to phone company networks and what highly specialized cables are necessary.