VLAN's VS subnets...

TMM3

I would like to see if somebody could explain to me briefly a benefit to using vlans as opposed to using strictly subnets. I know the definitions of both of them and have implemented both on a small scale and understand that vlans are l2 and subnets are l3 and some of the differences between them. I understand that the appropriate way to assign vlans is to assign each vlan its own subnet. Now if the reason for a vlan is to separate broadcast domains and secure areas of the lan, Im not seeing why implement a vlan ontop of implementing different subnets which do almost the same concept. Possibly to further divide subnets, or group subnets together?

I realize I'm a newb and there is something I am missing here because vlans are very popular and there must be a reason for them. Could somebody help me out here?

I hope that I have explained myself well.
Thank you in advance

iowatech

In a nutshell, routing purposes.
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VLANs: Sometimes there is so much traffic in one specific area of a network (subnet) that it makes sense to put those devices into their own virtual lan so they don't affect the bandwidth of the entire LAN. Or to split voice and data away from each other is another example.

Subnets: Routing purposes.

darkuser

vlans are layer two
and subnets layer3

Pash

Vlans offer a manageability for admins, you might need to divide switches on the network for a reason. As darkuser bluntly put vlans are L2 subnets L3 but remember all network traffic is L2 until it needs to go to its gateway to find a route to another network.

APA

Implementing VLANs gives you the added elements of manageability and scaleabilty according to your organizations layout.

Imagine this right..... Your accounting department is full but they hired additional staff, now this additional staff will be situated in the marketing department downstairs. Two different subnets....... The marketing subnet doesn't have the same privileges as accounting over the network.... What do you do??

Now if you have implemented VLANS you could assign the switchports to the accounting VLAN that the additional staff are patched into downstairs so logically they are still part of the accounting VLAN even though they are physically located elsewhere.

Now what if you didn't have this opportunity? Well the additional staff would have to obtain an address on the Marketing subnet and you would have to configure specific access from the marketing subnet for those addresses assigned to them to ensure they have the same access as the accounting staff upstairs..... (Major Administrative overhead.......)

VLANs give you the benefit of logically grouping users together regardless of their physical location (As long as they are contained within the same VTP domain......)

Hope this explains the theory behind the VLAN madness..

TMM3

What it looks like that I was or still am lacking is the real world production experience in a large network to validate the use and implementations of vlans.
Thank you guys for chiming in. I understand the use of them a bit more and see where they would be useful to some extent.