In today‘s complex business networks that comprise many virtual LANs and subnets, a Layer 3 switch plays an important role in many systems.
But do you need this on your network? Let‘s see.

What is a Layer 3 switch?

Simply put, a Layer 3 switch combines the functionality of a switch and a router. It acts as a switch to connect devices that are on the same subnet or virtual LAN at lightning speed and has built-in IP routing intelligence to function as a router. It can support routing protocols, inspect incoming packets, and may even make routing decisions supporting source and destination addresses. This is often how a Cisco Layer 3 switch acts as both a switch and a router.Often referred to as a multi-layer switch, a Layer 3 switch adds a lot of flexibility to a network.

Characteristics of a layer 3 switch

The characteristics of a Layer 3 switch are:

It comes with 24 Ethernet ports, but no WAN interface.

It acts as a switch to connect devices within the same subnet.

The switching algorithm is simple and is the same for most routed protocols.

It operates on two OSI layers: layer 2 and layer 3.

Purpose of a Layer 3 switch

There is a lot of confusion about using a Layer 3 switch because, in a traditional configuration, routers operate at Layer 3 of the OSI model while switches operate at Layer 2. So how does this Layer 3 switch fit into this model? Also, the name "layer 3 switch" confuses because switches normally operate from layer 2.

Layer 3 switches were originally designed to improve routing performance in large networks, especially corporate intranets. To understand the purpose, let‘s go back a bit in time to see how these switches evolved.

Layer 2 switches work well when there is low to medium traffic on VLANs. But these switches would hang when traffic increased. So, it became necessary to increase the functionality of Layer 2.

One option was to use a router instead of a switch, but then routers are slower than switches, so this could lead to slower performance.

To overcome this disadvantage, the researchers considered implementing a router within a switch. Although technically feasible, it was not the ideal choice because Layer 2 switches operate only on the Ethernet MAC frame while Layer 3 handles multiple routing protocols. The researchers felt this was too complicated, so they came up with the idea of a Layer 3 switch that would act like routers with fast-forwarding done through the underlying hardware.

This is why the most difference between Layer 3 switches and routers lies within the hardware. If you take a look at the hardware of a Layer 3 switch, you will see a mix of traditional switches and routers, except that the router software logic is replaced by integrated circuit hardware to improve performance.

Also, a Layer 3 switch router will not have WAN ports or other WAN features that you would normally see on a traditional router.

Benefits of a Layer 3 switch