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What is the use of VLAN in networking.Can any one point out a scenario where VLAN is useful

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5 Answers 5

We have one set of switches and separate vLans for general traffic, visitor connections (Internet only), Management traffic (iLO), SAN (iSCSI), and health remediation.

The Wikipedia article has a lot more information, including uses.

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Chris can you explain elaborate –  JavaUser Sep 16 '10 at 16:47
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@JavaUser, We have one set of switches; all traffic is confined to one vLan or another and a security appliance allows certain traffic to route from one vLan's subnet to another. This keeps the traffic from each completely separate (except as defined in the security appliance), while actually running it all over one set of switches. –  Chris S Sep 16 '10 at 17:02
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Initially because is more price-efficient to use a single physical infrastructure split up into multiple (virtual) LANs than it is to build separate physical infrastructures for each LAN environment.

At the root, that's it. Use logically separation rather than physical separation.

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In a large campus switched network, you need to use VLANs to separate the broadcast domains into smaller more manageable units. Once you get beyond a few hundred devices in your broadcast domain, your broadcast traffic gets to the point where it's making a serious negative impact on your network. Try finding a broadcast storm on a huge flat network with thousands of devices. Not so easy. Also, ACLs.

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If you have to ask about VLAN uses then you've never worked with a managed switch environment. The uses are limited only by one's imagination and I've seen some very creative uses. The basic scenario is segregating traffic on a single switch. If you have two offices on a single switch you can put them on different VLANs so to those machines it looks like they're on different physical switches. If you hear the term Layer 3 switch that means the switch can act like a router to route traffic between those two VLANs without using an external router. A step up from that is if you have another group of computers on the other side of the building that you want to be part of one of those VLANs. You can do what's called trunking to do that across switches so despite being on different physical switches the machines all work like they're on the same switch.

There are a lot of other uses but it's hard to explain in a short text reply. There are books from Cisco just covering the topic of VLANs

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In a word "segmentation". For example if you want to run more than one separate network in a single location you either have to run multiple network cables or use a VLAN...

See http://www.youtube.com/watch?v=9LHwbuWz1UM for a simple explanation from Cisco

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