The role of switches in your network Switches serve as an efficient central point for your local area network, allowing the exchange of information between various devices on the network. These devices can be things like computers, servers, routers, printers, and firewalls. Switches have several advantages over hubs; for instance, they allow you to divide your network into multiple segments. Segmentation of a network is beneficial because it reduces the number of data collisions that occur as several computers attempt to transmit data at the same time. A frame is a predetermined amount of data that has been packaged for transmission. Frames are further broken into bits, zeros and ones, before they are forwarded through the network to the destination computer. If more than one computer attempts to communicate on the network at one time a data collision will occur leaving the network inaccessible for a short time. Data collisions are analogous to conversations with several people - if everyone speaks at the same time then nothing is heard, whereas if people wait until no one else is speaking before they begin the conversation is allowed to continue uninterrupted. A switch forwards frames only to the port that connects to the intended destination of that data. Hubs handle network traffic less efficiently, broadcasting frames to all ports and thereby creating more data collisions. How do switches work? Switches build a “switching table” to forward packets of data directly to their destination. This switching table, which is stored in the switch's memory, tells the switch which computer or computers are connected to each one of its ports. Specifically, the switching table stores the Media Access Control (MAC) addresses for computers, printers and other network devices that plug into ports on the switch. A MAC address is a hardware address that uniquely identifies each device on a network. These are hard-coded onto network interface cards (NICs) and must be unique. Since switches build these tables, they are more efficient and send frames only to that port on which the device resides. Again, a hub has no table built into it and instead blindly sends all frames it receives out all ports. Not all switches are created equal There are two types of switches: managed and unmanaged. Unmanaged switches are similar to hubs in that there is no configuration needed (or possible) and they are ready to go out of the box. Unmanaged switches are ideal for small, simple networks. Generally, unmanaged switches can be purchased for roughly the same amount as a hub. Smart shopping on the web can often turn up unmanaged switches for comparable prices to hubs and the improved performance of your network is worth a few dollars more. Once unpacked, powered up, and connected to your network, they will build a switching table automatically and forward frames out the appropriate ports with no additional user intervention. Your network will run more efficiently with very little effort on your part. If you have a more robust network with a need to grow, look toward a managed switch. A managed switch gives you more control over your network. By assigning an IP address to your managed switch, you can remotely monitor and administer certain areas of your network and the functions of the switch. Currently, much of this administration and configuration can be done through a web browser, easing administrative and management tasks. In addition, most managed switches will collect and report information about the performance of the network, including problems on specific ports and the workstations or servers attached. This reporting function is a good way to manage the growth of your network or to troubleshoot problems. Additional functionality of managed switches includes their ability to set up broadcast domains within your network - in the past this had only been possible on routers, which are much more expensive per port. Finally, as your network grows it is a good idea to have a managed switch at the center of your network. With this setup you can run single computers on your managed switch ports, or place additional switches or hubs on those ports to allow for scalability. Location of the switch The size and complexity of your network should determine where the switch is placed. Generally, for smaller networks with fewer network devices than the number of ports on the switch, each device can be directly connected into the managed switch (as pictured below). In this scenario, the switch can provide dedicated 10 or 100 Mbps bandwidth to the devices that are directly connected to its ports, depending on the network interface card in each device and the configuration of the port settings on the switch. A second option for installing a managed switch is to use it as a central connection point for multiple network segments. In this configuration, it would act as an aggregate device for other switches and hubs in your network (as pictured below). Since the switch can offer dedicated bandwidth to its ports, this allows for greater bandwidth to the aggregated hubs and switches, and therefore to the end stations as well. By extending the network to other switches or fast hubs, your network can continue to grow without significant bandwidth delay. Virtual Local Area Network (VLAN) overview Another advantage of managed switches is their ability to support Virtual Local Area Networks, or VLANs. A VLAN is a logical segment of your network that is independent of location. In other words, VLANs are groupings of ports on a switch that create separate collision and broadcast domains and allow you to organize groups of computers according to your needs (as pictured below). For example, with a VLAN you can group all of the computers, servers and printers of a specific department together, independent of the geographic location of those devices. For your organization, this means that you can separate your departmental computers from other departmental computers and from administration computers without the need to create a separate physical network. VLANs increase the security and scalability of your network, and enhance network management. Through the use of VLANs, you can have all of your computers on the same physical network and not worry about unauthorized access to confidential files. Also, by increasing the number of collision and broadcast domains, and therefore decreasing the number of computers affected by each collision or broadcast, VLANs reduce network congestion (since these events are not forwarded to other VLANs). VLANs can exist in small networks, or in networks that span large geographic areas. Within a small network the ports on one managed switch are grouped together to create the VLANs. For larger networks several managed switches are paired together with routers. Resources and vendors http://computer.howstuffworks.com/lan-switch.htm A tutorial on switching, network basics, VLANs, etc. found at LAN switch technology. http://www.cisco.com/univercd/cc/td/doc/product/software/ios113ed/113ed_cr/switch_c/xcvlan.htm Introduction to VLANs. This document is fairly technical. http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/1214ea1/3550scg/swvlan.htm Comprehensive and technical description of creating and maintaining VLANs. Technical definition website. Switch Vendors - While no means comprehensive, this is a quick “product map” providing an overview of the lower-end offerings from some of the leading switch companies. All of the models mentioned here are described as supporting VLANs and having some management capability. Much of this information on specific models came from the vendor's websites or from the Dell'Oro site: http://www.delloro.com/ The vendors are listed alphabetically and no recommendations are implied. 3COM LAN SWITCHES Workgroup/desktop models This link contains both unmanaged entry-level switches and managed multilayer gigabit Ethernet switches. Also there is a switch finder to identify with switch is appropriate for your needs. Their entry-level managed switch are the following models: SuperStack 3300, 3900, 4300, 4400, 4900, 4200 Series. ALCATEL Entry-level switches: OmniStack 4000 & 5000 Series found at ALLIED TELESYN Allied Telesyn has a wide product range. You can find both layer 2 unmanaged and managed switches as well as layer 3 switches and layer 2 to layer 4 switches. Entry-level managed switches: Allied Telesyn AT-8XXX Series http://www.alliedtelesyn.com/products/default.aspx AVAYA Entry-level managed switches: Cajun P11X, P120, P220, P330, P133 Series P130 Workgroup Ethernet Switch Product Summary and P330 Ethernet Stackable Switching System Product Summary found at: CISCO Ciscos entry-level products, the Catalyst 2900 series switches, are highly capable managed switches that can serve as aggregate switches in moderate sized networks. http://www.cisco.com/en/US/products/hw/switches/index.html DELL Entry-level managed switches: PowerConnect 3000 Series found at ENTERASYS Entry-level managed switches: SmartStack Series, SmartSwitch Series, Vertical Horizon Series, especially the Vertical Horizon VH-2402S2 http://www.enterasys.com/products/switching/VH-2402S2/ EXTREME Entry-level managed switches: Summit 24e2 http://www.extremenetworks.com/libraries/prodpdfs/products/summit24e3e2.asp FOUNDRY Entry-level managed switches: EdgeIron series http://www.foundrynetworks.com/products/l23wiringcloset/edgeiron/2402_4802CF_24G.html HEWLETT-PACKARD Entry-level managed switches: ProCurve 2424, 2512, 2524 http://www.hp.com/rnd/products/switches/switch2524-2512/summary.htm LINKSYS Linksys offers a wide variety of products from small office/home office use to unmanaged and managed business solution switches. SOHO switches and Managed switches found at: NETGEAR Netgear products range from desktop switches up to business solution managed switches. This site provides a comparison chart of their products and further reading on managed switches and VLANs. Entry-level managed switches: NETGEAR FSM726S, FSM750S http://www.netgear.com/products/switches.html NORTEL Nortel has acquired several companies, so it has a large product line, from Layer 2 - 7 routing switches to VPN switches to entry-level switches. Entry-level managed switches: Nortel Networks BayStack 350, 420, 450, 460, 470, BPS 2000 http://www.nortelnetworks.com/products/data/switch.html SMC Entry-level managed switches: TigerSwitch http://www.smc.com/index.cfm?action=products_choose_product&cat_id=8&prodCat=Managed%20Switches
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| Managed Switches and Virtual LANs |
Switches are a useful element of network infrastructure. In this article, you'll find a full explanation of switches and the differences between managed and unmanaged switches. For example, with managed switches you can set up a virtual local area network (VLAN) and administer your network more effectively. A list of managed switch vendors is included.
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