Network Switch

Network Switch

A network switch is a device that provides a switching function in a data communications network. Data communication in a computer network involves the exchange of data between two or more entities interconnected by communication links and subnetworks. A network switch is an intermediate station which interconnects the communication links and subnetworks to enable transmission of data between the end stations. Switching involves transferring information, such as digital data packets or frames, among entities of the network. A switch functions as an interchange and provides path switching for data being transported over a network. Typically, a switch supports one network protocol (e.g. Ethernet), meaning that the switch manages data in a particular format. Switched  local area networks use a network switch for supplying data frames between network stations or other network nodes (such as routers or gateways), where each network node is connected to the network switch by a media. A network switch for routing packets between network buses includes a set of input switch ports for receiving packets arriving on the network buses, a set of output switch ports for forwarding packets outward on the network buses, and a switch fabric for routing packets between the input and output switch ports. Each input switch port includes a memory for storing packets arriving on a network until the switch fabric can forward them to an output switch port. The input port may convert each packet arriving on a network bus to a sequence of cells of uniform size which can be efficiently stored in uniformly-sized buffer memory storage locations until the input port can forward them in proper sequential order through the switch fabric to one of the switch's output ports. Each output switch port may also include a memory for storing packets it receives via the switch fabric until the port can forward them outward on a network bus. Each output switch port stores each cell sequence arriving from an input port in its own buffer memory. The output port later reassembles them into the packet from which they were derived, and then forwards the packet outward on an other network bus. Local-area network (LAN) switches are at the core of all networks, providing high-speed connectivity, applications, and communications systems. Today’s networks not only need to efficiently and securely transmit bandwidth-intensive data, voice, video, and wireless applications, they also need to provide for evolving traffic patterns, new services, and optimized application performance. To meet current and future network needs.

Image ; Linksys Switch

Function

As with hubs, Ethernet implementations of network switches support either 10/100 Mbit/s or 10/100/1000 Mbit/s ports Ethernet standards. Large switches may have 10 Gbit/s ports. Switches differ from hubs in that they can have ports of different speed.

The network switch, packet switch (or just switch) plays an integral part in most Ethernet local area networks or LANs. Mid-to-large sized LANs contain a number of linked managed switches. Small office, home office (SOHO) applications typically use a single switch, or an all-purpose converged device such as gateway access to small office/home office broadband services such as DSL router or cable, Wi-Fi router. In most of these cases, the end user device contains a router and components that interface to the particular physical broadband technology, as in the Linksys 8-port and 48-port devices. User devices may also include a telephone interface to VoIP.

Image; Cisco Catalyst-6500

In the context of a standard 10/100 Ethernet switch, a switch operates at the data-link layer of the OSI model to create a different collision domain per switch port. If you have 4 computers A/B/C/D on 4 switch ports, then A and B can transfer data between them as well as C and D at the same time, and they will never interfere with each others' conversations. In the case of a "hub" then they would all have to share the bandwidth, run in half-duplex and there would be collisions and retransmissions. Using a switch is called micro-segmentation. It allows you to have dedicated bandwidth on point to point connections with every computer and to therefore run in full duplex with no collisions.

Image; Cisco Nexus 7000

Layer-1 Switches

A network hub, or repeater, is a fairly unsophisticated network device, and is rapidly becoming obsolete. Hubs do not manage any of the traffic that comes through them. Any packet entering a port is broadcast out or "repeated" on every other port, except for the port of entry. Since every packet is repeated on every other port, packet collisions result, which slows down the network.

Hubs have actually become hard to find, due to the widespread use of switches. There are specialized applications where a hub can be useful, such as copying traffic to multiple network sensors. High end switches have a feature which does the same thing called port mirroring. There is no longer any significant price difference between a hub and a low-end switch.

Layer 2

A network bridge, operating at the Media Access Control (MAC) sublayer of the data link layer, may interconnect a small number of devices in a home or office. This is a trivial case of bridging, in which the bridge learns the MAC address of each connected device. Single bridges also can provide extremely high performance in specialized applications such as storage area networks.

Bridges may also interconnect using a spanning tree protocol that allows the best path to be found within the constraint that it is a tree. In contrast to routers, bridges must have topologies with only one active path between two points. The older IEEE 802.1D spanning tree protocol could be quite slow, with forwarding stopping for 30–90 seconds while the spanning tree would re converge. A Rapid Spanning Tree Protocol was introduced as IEEE 802.1w, but the newest edition of IEEE 802.1D-2004, adopts the 802.1w extensions as the base standard.

While "layer 2 switch" remains more of a marketing term than a technical term, the products that were introduced as "switches" tended to use micro segmentation and full duplex to prevent collisions among devices connected to Ethernets. By using an internal forwarding plane much faster than any interface, they give the impression of simultaneous paths among multiple devices.

Once a bridge learns the topology through a spanning tree protocol, it forwards data link layer frames using a layer 2 forwarding method.

Layer 3

Within the confines of the Ethernet physical layer, a layer 3 switch can perform some or all of the functions normally performed by a router. A true router is able to forward traffic from one type of network connection (e.g., T1, DSL) to another (e.g., Ethernet, WiFi).

The most common layer-3 capability is awareness of IP multicast. With this awareness, a layer-3 switch can increase efficiency by delivering the traffic of a multicast group only to ports where the attached device has signaled that it wants to listen to that group. If a switch is not aware of multicasting and broadcasting, frames are also forwarded on all ports of each broadcast domain, but in the case of IP multicast this causes inefficient use of bandwidth. To work around this problem some switches implement IGMP snooping.

Layer 4

While the exact meaning of the term Layer-4 switch is vendor-dependent, it almost always starts with a capability for network address translation, but then adds some type of load distribution based on TCP sessions.

The device may include a stateful firewall, a VPN concentrator, or be an IPSec security gateway.

Layer 7

Layer 7 switches may distribute loads based on URL or by some installation-specific technique to recognize application-level transactions. A Layer-7 switch may include a web cache and participate in a content delivery network.

Network switch can utilize the full throughput potential of a networks connection for each device making it a natural choice over a standard hub.

In other words, say for instance you had a network of 5 PCs and a server all connected with 10Mbps UTP cable. Using a hub, the throughput (10Mbps) would be shared between each device, with a switch each device could utilize the full 10Mbps connection.

When using a switch instead of a hub it is common place to create a faster throughput connection between the switch and the server (backbone).

For example if you had 10 PCs connected to the switch with 10Mbps cable then it would improve performance to use a 100Mbps connection from the switch to the server.

Here We take an configuration example of Cisco Catalyst  Express 500 Series Switch

(This is just an example to show the Internal "IOS-Internetwork Operating System", Interface of the Managed Switch )

 1.Type the ip-address of the managed switch( ex. Cisco Catalyst  Express 500 Series) in the address bar of the internet explorer or mozilla firefox and you will be prompted for user name & password in order to login into IOS (Internetwork Operating System)as shown in the above image.

 2.Once Logged in you can see the Dashboard of the switch where all the general information and health status of the switch will be displayed as shown above,you can check the temperature of the switch,bandwidth usage,packet error as shown above.

 3.In the above image you can see the Smartports Configuration and Configure.Here you can assign the port role to a specific port based upon needs (you can make port router,switch,guest,server,desktop etc.)

4.In the above image as you can see that one can go for complete port settings,its description and other functions

 5.Under "Express Setup" the network settings and the name of the host,subnet mask,gateway,IP Assignment Mode can be described as shown above

6.One can create VLAN based upon their organizational requirements .If you don't wish to create a VLAN then leave it as default,as shown above 

7.One can monitor the port status ,speed etc as shown above and also monitor the port statistics as shown in the image below , where one can monitor the number of transmitted bytes,packets and received also the error reports   

8.In the image above once clicking on "Alert Log" under monitor one can see the complete Alert Log its severity and description as well as time stamp.

 9.Under Diagnostics one can run a diagnostic test (which is automated and it will troubleshoot all the problems of the switch) as shown above.

 10. Under software upgrade one can upgrade the version of IOS and also check for the latest version. 

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