Vlans are amazing features when it comes to networking, they use the same physical medium to create subnets and traffic different data. To better understand how this works, let's imagine that our network switch is a building with several floors and apartments, access through the floors is done only via stairs. In our example each floor represents a Vlan and each apartment on each floor represents equipment such as printers and computers, or departments, or even different sites. Residents of the apartments are the data that travels through the network. Residents (data packets) of a particular floor (Vlan) are only able to communicate with the residents of the same floor. If there is a need to communicate with residents of another floor he needs to resort to the stairs (Gateway) that know how to route these dwellings to the other floors and the resident will be allowed to follow or not. Following this concept, we have the assurance that no "inhabitant" will enter floors that he is not authorized and thus we keep the network segmented and safe.
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