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Definition
It was not so long ago that switches were used in telecommunications primarily for placing telephone calls. Dialing a telephone number activated a series of switches to set up a voice path that could be as simple as the next office or as complex as a multinational conference call. Internetworks and the Internet are beginning to provide similar services for PC workstations, servers, and mainframes. The primary goal of any data network provider is to eliminate geographic and media constraints on connectivity while maintaining control over resources and costs. Embedding Layer 3 Switching into the network is being promoted as the best way to achieve this.

A variety of switch and router technologies are entering the market and creating confusion among network professionals. New terms such as Layer 3 switching, multilayer switching, routing switch, switching router, and Gigabit router are clouding the traditional distinctions between switches and routers. Furthermore, many wiring closet switches that traditionally employed simple Layer 2 switching are now offering Layer 3 switching functions or future options for Layer 3 capabilities. These changes make it difficult for network designers to understand and deploy effective network solutions.

It is clear that a new generation of Internet and intranet work processes are emerging and that users will benefit from both increased competition and new services. It is therefore important do demystify the hype and understand when and where Layer 3 switching is important by getting back to the basics.

Layer 3 switches are compared to traditional multiprotocol routers. It is demonstrated that Layer 3 Switching is simply a re-invention of the router using new switch based technologies. This seminar also reviews the basic data forwarding, route processing, and value-added functions that are required of any intelligent network node.
Network Basics

Understanding the Layers
Internetworking devices such as bridges, routers, and switches have traditionally been categorized by the OSI layer they operate at and the role they play in the topology of a network:

1.Bridges and switches operate at Layer 2: they extend network capabilities by forwarding traffic among LANs and LAN segments with high throughput.

2.Routers operate at Layer 3: they perform route calculations based on Layer 3 addresses and provide multi-protocol support and WAN access, but typically at the cost of higher latency and much more complex administration requirements.

Layer 2 refers to the layer in the communications protocol that contains the physical address of a client or server station. It is also called the data link layer or MAC layer.

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