BENEFITS AND RESTRICTIONS VLANS VIRTUAL LOCAL AREA NETWORKS

The primary benefit of the port based VLAN technology is the localization of traffic that it provides. This function can offer improvements in security and performance to stations assigned to a VLAN.

While the localization of traffic to VLANs can improve security and performance, it imposes some restrictions on network devices that participate in the VLAN. If a switch is operating in the “secure mode,” a group of users assigned to a single VLAN can communicate with one another freely, but cannot communicate with users on other VLANs without the services of a Network Layer (OSI Layer 3) routing device to make the connection between the VLANs. In the “open” mode, this restriction does not apply.

In order to set up a VLAN, all the network switch devices that are assigned to the VLAN must support the prestandard IEEE 802.1Q specification for port based VLANs. Before you attempt to implement a VLAN strategy, ensure that the switches under consideration support the 802.1Q specification.

TYPES OF VLANS VIRTUAL LOCAL AREA NETWORKS

There are a number of different strategies for creating Virtual Local Area Networks, each with their own approaches to defining a station’s membership in a particular VLAN.

1. Port Based Vlans

A port based VLAN switch determines the membership of a data frame by examining the configuration of the port that received the transmission or reading a portion of the data frame’s tag header. A four-byte field in the header is used to identify the VLAN. This VLAN identification indicates what VLAN the frame belongs to. If the frame has no tag header, the switch checks the VLAN setting of the port that received the frame. If the switch has been configured for port based VLAN support, it assigns the port’s VLAN identification to the new frame.

2. Secure Fast Vlans

Cabletron Systems’ SECURE FAST VLAN strategy takes a different approach to creating virtual LANs. In a SECURE FAST VLAN environment, the switches in the network recognize Network Layer routing requests and translate them. Based on this translation, the switches set up a connection between the end devices in the network.

3 Other Vlan Strategies

VLANs may also be created by a variety of addressing schemes, including the recognition of groups of MAC addresses or types of traffic. One of the best-known VLAN-like schemes is the use of IP Subnets to divide networks into smaller subnetworks. These other VLAN types offer performance advantages and disadvantages that can be quite different from those available with the port based VLAN strategy.

VIRTUAL LOCAL AREA NETWORKS

A Virtual Local Area Network is a group of devices that function as a

single Local Area Network segment (broadcast domain). The devices that

make up a particular VLAN may be widely separated, both by geography

and location in the network.

The creation of VLANs allows users located in separate areas or

connected to separate ports to belong to a single VLAN group. Users that

are assigned to such a group will send and receive broadcast and multicast

traffic as though they were all connected to a single network segment.

VLAN aware switches isolate broadcast and multicast traffic received

from VLAN groups, keeping broadcasts from stations in a VLAN

confined to that VLAN.

When stations are assigned to a VLAN, the performance of their network

connection is not changed. Stations connected to switched ports do not

sacrifice the performance of the dedicated switched link to participate in

the VLAN. As a VLAN is not a physical location, but a membership, the

network switches determine VLAN membership by associating a VLAN

with a particular port.

Pincture shows a simple example of a port based VLAN. Two buildings

house the Sales and Finance departments of a single company, and each

building has its own internal network. The stations in each building

connect to a SmartSwitch in the basement. The two SmartSwitches are

connected to one another with a high speed link.

In this example, the Sales and Finance workstations have been placed on

two separate VLANs. In a plain Ethernet environment, the entire network

is a broadcast domain, and the SmartSwitches follow the IEEE 802.1d

bridging specification to send data between stations. A broadcast or

multicast transmission from a Sales workstation in Building One would

propagate to all the switch ports on SmartSwitch A, cross the high speed

link to SmartSwitch B, and be propagated to all the switch ports on

SmartSwitch B. The SmartSwitches treat each port as being equivalent to

any other port, and have no understanding of the departmental

memberships of each workstation.

In a port based VLAN environment, each SmartSwitch understands that

certain individual ports are members of separate workgroups. In this

environment, a broadcast or multicast data transmission from one of the

Sales stations in Building One would reach SmartSwitch A, be sent to the

ports connected to other local members of the Sales VLAN, cross the high

speed link to SmartSwitch B, and then be sent to any other ports and

workstations on SmartSwitch B that are members of the Sales VLAN.

Alarm - Mini Alarm DVR, Wireless and Inteligent Alarm

Chipsilicon Presents World's Best Alarm Systems

For more detailed enquiry on the above products, please visit - shop.chipsilicon.com

====================================================
BioEnable Technologies Pvt Ltd, The Avenue, 2B, 2nd Floor, Opp Mega Centre
Pune Solapur Road, Hadapsar, Pune 411028, Maharashtra, India
Tel : +91 20 26810214, 65005360/1/2 Fax +91-20-30225587, TOLL FREE: 1800-209-2131
==========================================
BioEnable is the - Company Of The Year 2007 for Electronic Access Control System - Frost & Sullivan

TOLL FREE: 1800-209-2131