he nodes connected to each wiring closest switch are out of service. In contrast, if a Layer 2 switch crashes, the only nodes that lose service are the 8 to 16 or 24 devices connected to it. Moreover, the cost to purchase www.TechnicalPDF.com redundant Layer 2 switches is high because there are SO many of them. In a five-story building, there could be a total of 40 Layer 2 switches in wiring closets and only six in the backbone. See Figure 2-2 for switches in LAN backbones. There are instances, however, when high-level employees such as CEOs are connected to a dedicated Layer 2 switch. In these cases, components within the wiring closet may be duplicated to avoid outages. In addition, IT staff closely monitor these senior employees' equipment connections SO that if they do break down, they can be repaired or quickly replaced. backbone cabling duplicate switch ports. backup becomes active. wiring closet www.TechnicalPDF.com Data center Figure 2-2 Switches in LAN backbones. Layer 3 Switch Redundancy in the Backbone Because core Layer 3 switch failures impact many nodes in networks, there are often redundant Layer 3 switches. Medium- and large-sized organizations often have redundant switches in their backbone network SO that if one switch is out of service traffic can be rerouted to a different Layer 3 switch. In addition to or instead of having redundant switches in backbones, components within each core switch can be duplicated, particularly those components such as power supplies that fail more frequently than other components. And importantly, there may be redundant www.TechnicalPDF.com switches within data centers. When either of these two things is done, there are rarely LAN outages. Organizations consider a variety of levels of redundancy for core switches, including the following: Purchase of a separate, duplicate switch that can take over if one fails. Installation of redundant power supplies in the switch. (A power supply converts AC power to the low-voltage DC power required by computers.) Switches are i