arturo.guzman Thu, 05/29/2008 - 07:40
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Vlan's are a Virtual Lan's and when you configure it is like the switch is to divide in the number of the individuals switches like a number of vlan's that you configure.

In this case each vlan works like a individual switch.

jeeveshwarni Thu, 05/29/2008 - 12:20
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VLAN - devide a physical network into multiple subnetwork to secure network and break a broadcast domain.

Anas Naqvi Fri, 10/18/2013 - 01:55
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A VLAN is a group of end stations with a common set of requirements,  independent of physical location. VLANs have the same attributes as a  physical LAN but allow you to group end stations even if they are not  located physically on the same LAN segment.

VLANs are usually associated with IP subnetworks. For example, all the  end stations in a particular IP subnet belong to the same VLAN. Traffic  between VLANs must be routed. LAN port VLAN membership is assigned  manually on an port-by-port basis.

For more information please check the following link,

chandra_rc16 Fri, 10/18/2013 - 02:32
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VLANs (Virtual Local Area Networks) are created to seperate layer 2 traffic.Generall types of traffic include.

1. Multicast (Video streaming)

2. Network Management Traffic (SNMP messages, CDP Messages, BPDU's etc)

3. VoIP (Voice Traffic)

4. User traffic

So  let us assume there are no VLANs, what happens here is: Since the basic  functinality of a switch is to flood if the destination MAC address is  not present in its CAM table (And also if it's cam table is full).. we  will see a lot of broadcast messages all of the above said usages.

And  also let us take the example of the VoIP ... since there are no VLANs  and switch is expereincing a lot of broadcast messages and the users are  using VoIP obviously some of the packets will drop because of the  broadcast storm that switch is experiencing. So there will be a lot of  disturbance in that call.. And same thing applies all the above types of  traffic.

So  inorder to overcome the above issues we need seperate the traffic types  which means broadcast domains by creating virtual LANs.. in this way  VLANs seperate layer 2 traffic to enhance stability and security.

Agian  how securty is achieved : simple inorder to communicate between two  VLANs you need a layer3 device (a router) where we cann assign ACLs like  which VLANs traffic to pass or bypass it.

And  also VLANs are location independent it means it can span to multiple  switches.. untill the user belong to the same VLAN he can communicate  with the members in same VLAN without using layer3 device....

And also excellent info is availbale @ :

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