A Network Switch is a computer networking device that connect devices on a computer network by using packet switching to recieve, process, and forward data to the destination device
Network Switch look In Diagram
Layer-2 devices build hardware address tables, which at a minimum contain the following:
•Hardware addresses for hosts
•The port each hardware address is associated with
Using this information, Layer-2 devices will make intelligent forwarding decisions based on the frame (or data-link) headers. A frame can then be forwarded out only the appropriate destination port, instead of all ports.
Layer-2 forwarding was originally referred to as bridging. Bridging is a largely deprecated term (mostly for marketing purposes), and Layer-2 forwarding is now commonly referred to as switching.
There are some subtle technological differences between bridging and switching. Switches usually have a higher port-density, and can perform forwarding decisions at wire speed, due to specialized hardware circuits called ASICs (Application-Specific Integrated Circuits). Otherwise, bridges and switches are nearly identical in function.
Ethernet switches build MAC address tables through a dynamic learning process. A switch behaves much like a hub when first powered on. The switch will flood every frame, including unicasts, out every port but the originating port.
While hubs were limited to half-duplex communication, switches can operate in full-duplex.Each individual port on a switch belongs to its own collision domain. Thus, switches create more collision domains, which results in fewer collisions.
Like hubs though, switches belong to only onebroadcast domain. A Layer-2 switch will forward both broadcasts and multicasts out every port but the originating port. Only Layer-3 devices separate broadcast domains.
Because of this, Layer-2 switches are poorly suited for large, scalable networks. The Layer-2 header provides no mechanism to differentiate one network from another, only one host from another.
This poses significant difficulties. If only hardware addressing existed, all devices would technically be on the same network. Modern internetworks like the Internet could not exist, as it would be impossible to separate my network from your network.
Imagine if the entire Internet existed purely as a Layer-2 switched environment. Switches, as a rule, will forward a broadcast out every port. Even with a conservative estimate of a billion devices on the Internet, the resulting broadcast storms would be devastating. The Internet would simply collapse.
Both hubs and switches are susceptible to switching loops, which result in destructive broadcast storms. Switches utilize the Spanning Tree Protocol (STP) to maintain a loop-free environment. STP is covered in great detail in another guide. Remember, there are three things that switches do that hubs do not:
•Hardware address learning
•Intelligent forwarding of frames
Hubs are almost entirely deprecated – there is no advantage to using a hub over a switch. At one time, switches were more expensive and introduced more latency (due to processing overhead) than hubs, but this is no longer the case.
Network Switch Role in Network:-
Switches are most commonly used as the network connection point for hosts at the edge of a network. In the hierarchical internetworking model and similar network architectures, switches are also used deeper in the network to provide connections between the switches at the edge.
In switches intended for commercial use, built-in or modular interfaces make it possible to connect different types of networks, including Ethernet, Fibre Channel, RapidIO, ATM, ITU-T G.hn and 802.11. This connectivity can be at any of the layers mentioned. While the layer-2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as Ethernet and token ring is performed more easily at layer 3 or via routing. Devices that interconnect at the layer 3 are traditionally called routers, so layer 3 switches can also be regarded as relatively primitive and specialized routers.
Where there is a need for a great deal of analysis of network performance and security, switches may be connected between WAN routers as places for analytic modules. Some vendors provide firewall, network intrusion detection, and performance analysis modules that can plug into switch ports. Some of these functions may be on combined modules.
Through port mirroring, a switch can create a mirror image of data that can go to an external device such as intrusion detection systems and packet sniffers.
A modern switch may implement power over Ethernet (PoE), which avoids the need for attached devices, such as a VoIP phone or wireless access point, to have a separate power supply. Since switches can have redundant power circuits connected to uninterruptible power supplies, the connected device can continue operating even when regular office power fails.