What is Layer 3 Switch? – Brief Introduction

The network layer (Layer 3) of the OSI model is responsible for packet forwarding between intermediate routers and different networks. The routers are working in layer 3 of the OSI model, but usually, it’s seen that the routers are considerably slower than layer 2 switches.

The layer 2 switches cannot communicate in different networks, because they cannot read a layer 3 packet. But layer 3 switch is a device that can read and forward traffic based on layer 3 information at a very high speed.

The layer 3 switches are very essential in enterprise networks and particularly design with many subnets and virtual LANs. Layer 3 switches are like a high-speed router without WAN connectivity.

It also acts as a switch because it connects devices on the same IP network or virtual LAN, and it performs at or near wire speed.

Usually, router-on-a-stick is a simple way to implement inter-VLAN routing because routers are mostly part of each network. But, most enterprise networks needed high speeds packet-processing.

To gain this required high speed they are using multilayer switches. The Layer 3 switches generally giving millions of packets per second (PPS) throughput. All Catalyst multilayer switches support the following Layer 3 interfaces:

·         Routed port- The routed port is just like a physical interface on a Cisco Router.
·         Switch virtual interface (SVI) – It is a virtual-routed interface for routing between different VLANs. It is also being used to connect the switch remotely.

All Layer 3 Cisco Catalyst switches can work as router and support routing protocols, but numerous models of Catalyst switches require updated software for specific routing protocol features.

The catalyst 6500 and 4500 series approximately perform all functions of OSI layer 3 by default using hardware-based switching but catalyst 2960 series required IOS release 12.2(55) or higher to support static routing.

The Catalyst 3560 and 45 series using the Layer 2 interface by default. The catalyst 6500 series uses Layer 3 interfaces by default. So, depending on the series of the switch we can change the switch port between Layer 2 and Layer 3.  We can change the switch port using the “switch port” and no switchport” command an interface mode.