What are the pros and cons of designing an entire network using VLANs rather than design the network only using subnets?
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4VLANs are layer-2, subnets layer-3. Any modern network of any size will have both. – Ricky Beam Jan 14 at 2:21
There's no discrepancy between VLANs and IP subnets - they go hand in hand.
Organizing your network into different IP subnets enables you to provide a (security) structure and to limit the size of each broadcast domain (instead of having a single large one). Without VLANs, subnetting requires separate switches for each subnet and separate cabling for each interconnect between switches and routers.
VLANs enable you to use the same L1/L2 infrastructure - switches and interconnects - for all (some) VLANs. That way, you save on a lot of hardware and cabling and can handle changes very flexibly.
VLANs are used to use same broadcasting domain over different switches and/or have different broadcast domains on one switch. In normal scenario we can't use nodes from two broadcast domains in an one switch
