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Switches (Cisco)
Network Switch
A Network switch is a device that filters, forwards, or floods frames based on the destination address of each frame. The switch operates at the data link layer of the OSI model. A network switch can also be termed as an electronic or mechanical device that allows a connection to be established as necessary and terminated when there is no longer a session to support.
Switches perfom their routing functions at the layers 2 model of the OSI. Some switches process data at the Network Layer (layer 3), are referred to as layer 3 switches or multilayer switches. Switches form an integral parts in networking LAN or WANs . Small office, Home office ( SOHO) applications normally, use a single or an all purpose switches .
As mentioned earlier, switches operates at the data-link layer of the OSI model, switch function is to create a different collision domain per switch port. Let take an example, Four computers PC 1, PC 2, PC 3, PC 4 attached to switch ports, then PC 1 and PC 2 can transfer data between them so as PC 3 and PC 4, simultaneously without interfering with each other's conversations. Unlike a hub, which allows the sharing of bandwidth by all port, run in half-duplex and is prone to collisions of frames and retransmissions.
With some ISPs and other networking environments where there is a need for much analysis of network performance and security, switches may be connected between WAN routers as places for analytic modules. Some switches provide in built firewall, network itrution detection and performance analysis modules that can plug into switch ports.
While switches may learn about topologies at many layers and forward at one or more layers, they do tend to have common features. Modern commercial switches use primarily Ethernet interfaces, which can have different input and output speeds of 10, 100, 1000 or 10,000 megabits per second (Mbps). Switch ports almost always default to full-duplex, unless there is a requirement for interoperability with devices that are strictly half duplex. Half-duplex means that the device can only send or receive at any given time, whereas full-duplex can send and receive at the same time.
 
Features and Functions of a Switch
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