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Wikipedia Defination of VLAN

Posted on 2011-03-03
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I think wikipedia defination of vlan is wrong...
A virtual LAN, commonly known as a VLAN, is a group of hosts with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location. A VLAN has the same attributes as a physical LAN, but it allows for end stations to be grouped together even if they are not located on the same network switch. Network reconfiguration can be done through software instead of physically relocating devices.

A virtual LAN, commonly known as a VLAN, is a group of hosts with a common set of requirements that communicate as if they were attached to the same collision  domain..

Please correct me if i am wrong...
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Question by:tech2010
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Paul Solovyovsky earned 668 total points
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It's correct.  Broadcast Domain is your subnet which is a VLAN.  Multiple VLANs use a collision domain (the physical switch)


good def:

Basically, a collision domain is a network segment that allows normal network traffic to flow back and forth. In the old days of hubs, this meant you had a lot of collisions, and the old CSMA/CD would be working overtime to try to get those packets re-sent every time there was a collision on the wire (since ethernet allows only one host to be transmitting at once without there being a traffic jam). With switches, you break up collision domains by switching packets bound for other collision domains. These days, since we mostly use switches to connect computers to the network, you generally have one collision domain to a PC.

Broadcast domains are exactly what they imply: they are network segments that allow broadcasts to be sent across them. Since switches and bridges allow for broadcast traffic to go unswitched, broadcasts can traverse collision domains freely. Routers, however, don't allow broadcasts through by default, so when a broadcast hits a router (or the perimeter of a VLAN), it doesn't get forwarded. The simple way to look at it is this way: switches break up collision domains, while routers (and VLANs) break up collision domains and broadcast domains. Also, a broadcast domain can contain multiple collision domains, but a collision domain can never have more than one broadcast domain associated with it.

copied from :http://www.techexams.net/forums/ccna-ccent/19808-collision-domain-vs-broadcast-domain.html
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by:Don Johnston
Don Johnston earned 664 total points
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I concur.

However, I would clairify a couple of points.

Since most hosts today connect to a switch and that full duplex is enabled, collisions simply don't occur.

And broadcast frames are not unswitched. They are switched but unlike unicasts, they are replicated to all ports (flooded).
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by:aleghart
aleghart earned 668 total points
ID: 35030115
With switched networks, you don't have collisions, so defining VLAN by collision domain doesn't make much sense.  Broadcast floods all ports of the LAN or VLAN spanning multiple switches, so is appropriate.

I don't think I've seen a hub in maybe 15 years.  But isn't a WiFi LAN is a collision domain? So you can't ignore it.  I have  a WiFi WAP with multiple VLANs, and that gets confusing.
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