How Is VLAN Implemented?
Virtual local area networks are created by splitting traffic on a network into several separate networks even though those networks continue to run their traffic over the same physical network infrastructure. VLANs enable companies to run different types of traffic over the same network. An example of this is where businesses run their telephone system over the data network.
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Network Infrastructure
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Devices connected to a network are called “nodes.” A node may be a computer, printer, fax machine or an other type of “Data Terminating Equipment.” The nodes are connected together by cables, but those cables cannot run from one node to another. The network needs a central device where all cables converge. This way a node, connected to only one cable, can contact many other nodes. The connecting piece of hardware for this function is either a hub or a switch.
Hubs and Switches
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A hub is the simplest form of network infrastructure. Networks with a hub cannot implement VLANs. This is because the hub has no computing power; it is just an electronic box with a row of sockets. Each node on the network connects to one of the sockets on the hub. Any signal arriving in on one of these sockets (called “ports”) is immediately copied onto all the other cables connected to the hub. This multiplies network traffic. A more sophisticated form of network controller is called a switch, or switching hub. The basic switch is the same as the hub, except it examines incoming data, which is addressed to a destination and only repeats the data onto the port it has associated with that address. This basic switch is called an “unmanaged switch.” It does not have a user interface offering facilities to an operator and so cannot be configured to operate VLANs. On the other hand, managed switches can.
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Managed Switches
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Companies wanting to implement a VLAN need to have a managed switch at the center of their network. Managed switches fall into two categories: enterprise switches and smart switches. An enterprise switch has a console with a keyboard where the operator can nominate which connections form part of which VLANs. A smart switch looks like a hub, or an unmanaged switch, except that it has the computing power to offer configuration options. Any of the computers connected to the smart switch can remotely act as its console. This gives the smart switch the functionality of an enterprise switch, but at a much lower price.
Implementation
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After defining each group that will become nodes on each VLAN, the ports on the switch belonging to each named group are set with the property of the VLAN name. Some ports can be labeled as “trunk” lines. These ports will carry traffic from all VLANs. Trunks are used where traffic has to travel between switches. The traffic is divided out into separate VLANS only when it is destined to a DTE. Switch-to-switch traffic can carry messages from all the VLANs.
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References
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