Everyone knows that a typical switch is used to forward traffic (or packets) from the router to endpoint devices (computers, phones, tablets, iOT, etc). Sometimes, it is useful or even necessary to isolate broadcast traffic in a large network. This can be useful to help manage bandwidth utilization (QoS) by isolating and prioritizing certain traffic for certain devices. A great example is VOIP. In a typical situation, there may be a mix of wired and wireless devices in the single subnet which might include all of the IP Phones for the site. We may want to keep all of the voice traffic isolated from the other data traffic. The first thing a VLAN does is to create a separate broadcast domain. By utilizing VLAN, we can assign all of the IP Phones as a group in a VLAN and other networked devices to a different VLAN. This is a virtual creation of separate subnets, the traffic for the IP Phones in a particular VLAN can talk directly to the IP Phones without incurring the overhead associated with non-VOIP traffic. The devices connected to a VLAN will only process traffic intended for them based on protocol. Also, other uses for separation can be for supporting multiple companies in shared office space, supporting surveillance cameras, separating NAS traffic from other print/file traffic, etc. In summary, the use of VLAN can help reduce overhead on large networks by reducing unnecessary broadcast traffic heard by each device.
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