Using Switches in Your LAN

Local Area Network technologies have evolved over the past few years. With new technology upgrades like bridges and switches, the LAN ease and expandability for future application looked promising in early years of LAN technology invention. Switches improved upon bridges giving the same thought process speeds of a layer 2 device with a lower cost. Today's switches in local area networks are extremely improved compared to years before. Switches offer capabilities their operations, intelligent features, programmable features, and advanced features.

Switches were introduced in 1990 to give local area networks a device that would carry out actions much like a bridge but at a fraction of the cost. Switches optimized the use of layer 2 forwarding much like bridges. Since switches made their comfortable home as the top performing devices in local area networks, few people actually realize their power and speed as compared to other devices. Switches allow for dedicated bandwidth per port. This is in relation to it being used at the data link layer. Operating in this layer allows the device to forward information known as frames. It accomplishes this by reading frame header information to determine the destination device. In the header there are addresses the switch uses known as Media Access Control addresses. Switches are comparably faster than routers. When faster is used in this sense it is not referring to bandwidth capabilities, but rather its logical forwarding speed. Routers are devices that operate as a layer 3 device to forward packets based on logical addressing and hardwired addresses. This obviously takes more time to do than switching since a switch only examines the hardware addresses. Router are also required to encapsulate frames into packets which is the "speed bump" of the router. Switches have made leaps and bounds in the networking industry as of recent times, but other features are still being released each day. One such of the newest switching technologies is having the switch partially operate at layer 4. This technology allows for high security in your switched LAN by allowing the programming of the device to actually have traffic control features for protocols running at layer 4 and even to layer 7. The layer depends completely on the protocol or application and which layer it filters the protocol therefore operating in that layer. operations of a switch give it a certain advantage to have in a LAN, however their intelligent design is what makes them a large performance booster.

Switches use many complex pre-designed mathematical formulas to accomplish many tasks like controlling collisions. When a device is first connected to a switch, it sends out greeting packages including the MAC address using ARP (address resolution protocol) and the switch records this address and physical port location in a CAM table. It then uses a complex algorithm when a frame enters it port and directs it out of the correct port only. This in turn creates a separate collision domain per port. Collision domains occur when a segment of a network is contains a number of nodes that are susceptible to collisions with other devices in that segment. Switches offer flow control in order to create separate collision domains. Flow control controls and creates these domains by sending out jam signals when a port is overloaded so the signal is only sent out the high collision port. This creates a collision domain of a single port. Switches have much more advanced operations to programmed at birth for added performance. One such technology is Full-duplex operations which allows a device to receive and send data simultaneously. It is usually achieved by clock timing, internal electronic design and more complex algorithms, but by using these tools switches are able to avoid collisions. Switches also have advanced design features when it comes to forwarding frames. The store-and-forward process involves the switch receiving the whole frame and making a cyclical redundancy check before forwarding. This is useful for areas of bottlenecks because the information may have to be buffered before being sent through the smaller end of the bottleneck. Switches can also use a technique call cut-through forwarding. By using this, switches are able to forward pieces of a frame before receiving the entire frame thus reducing latency a great deal. However these forwarding processes are not determined solely by the switch, and they are in need of administration to ensure the correct forwarding process is used in the correct situations.

Along with design features and operations, switches have a vast array of programmable features for advanced technicians to control and implement. As stated before, a technician needs to know when forwarding process to use. The technician should also know the availability of extra features that switches have been introduced to over the years. The programming of a switch occurs in a command line by the use of a console port, a computer with appropriate software accommodations, and a rollover cable. The rollover cable connects between the PC and the switch's console port to create a programming connection. The PC uses a program such as telnet or likewise to enter the console of the switch to edit the 'heart' of the switch. The settings are saved on memory on the switch or sometimes in a TFTP server and are used by the switch as a kind of direction book to understand how it is supposed to be operating its mind. The most important programmable feature is setting passwords to stop people from changing the very programmed features the technician worked on setting up for hours. These passwords can be applied across the complex hierarchy of the actual console prompt. This console should be password protected at each level and also at any back door entrances. Static entries into the CAM table can be made using the terminal for specific devices a technician would want on a specific port. Technicians can also adjust the communication process and protocol for updating its CAM table by changing settings for update intervals. Another feature most switches are equipped with now is the ability to act as a DHCP server thus reducing costs for unneeded hardware. This feature and be customized as much as any DHCP server would in that the range of addresses it gives, lease time, and DNS and server information are all able to be edited to fit the administration needs. In addition to creating the DHCP server feature, the technician must also allow the switch to forward DHCP traffic so that receiving nodes will be able to obtain all the necessary information to gain access into the LAN. These simple programming features of switches can be setup by novice technicians, but other advanced features require more skill and training to full understand conceptual and physical implementation.

Some features of switches need to be setup by an extensively trained individual including the setup of a VLAN and traffic regulation. A technician must also know how to properly setup and administer virtual local area networks. Virtual Local Area Networks are logical network separations between a single switch. He could utilize this between every switch in the network even and subdivide the entire LAN based only on logical mapping. Of course this requires added planning and development so the reason for implementation should be worthwhile. For example, to stop certain broadcast traffic from effecting areas where those devices do not need to communicate with each other. A real life example would be with network located printers in a large switched LAN. In this situation only a certain amount of computers should need access to the closest printers in the area. The VLAN of printers and computers would separate the rest of the areas of the building or the separate virtual local area networks thus eliminating the printer's broadcasts from reaching other areas possibly those of high demand where the messages might have caused a collision. Switches are not alone in this world, however, routers are needed in order for separate virtual local area networks to communicate much as when two of the printer areas would need to share data or services. The biggest drawback from using virtual local area networks is the installation and setup difficulty along with compatibility between differing vendor switches where VLAN support is either not available or unrecognized by opposing vendor switches. Along with VLAN support, new switch technologies have enabled even better traffic control for switches. As stated before, layer 4 switches are becoming increasingly popular for their ability to filter traffic in the upper layers of the OSI model. The technician must know what he could use the new technology for and how he would put it in place. For example, if the switch was connecting a group of servers and then forwarding the server information to other switches in the LAN there would be high traffic. The technician could implement layer 4 switches to forward traffic to the correct server based on the service it is using, in turn creating a higher latency yet a much needed buffer in the extreme bottleneck situations. The programming for vendors can vary greatly even for same vendor switches of different model number. Cisco proprietary software/firmware is one of the most widely known and used terminal language for switches and routers. One of the new protocols used by Cisco is PoE or power over ethernet. It is setup on some switches for Cisco phones where the phone sends data and gets power for the phone on the same cable. Extreme caution needs to be taken on using this option with computer network cards. The excess power of used for the phone will burn components in a network card so documentation of configuration properties is of the utmost importance. A common knowledge of commands need to be shared by each the switch and the user programming it for flawless communication in a LAN.

Switches offer the capability of their operations, intelligent features, programmable features, and advanced features making them the most implemented device in local area networks today. With each advancement made was followed development for the future advancement. As the complexities of intranets grows into new categories of need such as phone use, traffic control, and performance, switches will be there to help provide a solution.