Cisco produces a wide variety of switch families. Inside each family are several specific models of switches. Cisco positions the 2950 series of switches as a full-featured, low-cost wiring closet switch. That means that you would expect to use this switch as the connection point for end-user devices, with cabling running from desks to the wiring closet. You would also use a couple of Ethernet ports to connect to other switches to provide connectivity between the wiring closet and the rest of the network.
Figure 8-1 shows one model of a 2950 switch, the 2950-24-EI switch, which provides 24 10/100 Ethernet interfaces and two Gigabit interfaces.
This particular model comes with 24 built-in 10/100 ports using RJ-45 connectors. Any of the ports can be used to connect to end-user devices or to other switches. This switch also includes two Gigabit Ethernet slots, on the right side of the figure, into which you can put the appropriate Gigabit Interface Converter (GBIC). You will read more about GBICs in Chapter 11, "LAN Cabling, Standards, and Topologies."
Switch commands refer to the the physical RJ-45 Ethernet connectors on a 2950 as interfaces. Each interface has a number in the style x/y, where x and y are two different numbers. On a 2950, the number before the / is always 0. The first interface is numbered 0/1, the second is 0/2, and so on.
Cisco switch operating systems can be categorized into two types: Internetwork Operating System (IOS) switches, and Catalyst Operating System (Cat OS) switches. When Cisco first entered the LAN switching arena, it did so by acquiring Crescendo Communications, which at the time, sold a line of switches called Catalyst switches. At the time of acquisition, Cisco already had sold a lot of routers, and, not surprisingly, those routers had a different user interface compared to Crescendo's switches. So, Cisco was faced with a dilemma: Should it update all the Crescendo Catalyst switches to use a user interface like the routers? Should it just continue to use the Crescendo Catalyst OS, now typically called the Cat OS, and that alone, on all future switches? The answer: Some Cisco switches use the Cat OS CLI, and some use the IOS CLI.
Cisco IOS switches use the same CLI as the router IOS. Even though the switches have a similar look and feel to the router IOS, they do not actually run the same IOS as the routers because switches and routers do not share a lot of the same functions and features. For instance, Cisco calls the 2950 operating system the 2950 switch software instead of IOS. However, because the look and feel of the user interface resembles the router IOS interface, most people simply call the 2950, and other switches that use the same CLI, IOS-based switches.
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