layer 3 switching operation and configuration

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

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

Layer 3 switches are essential in enterprise networks and are particularly designed for many subnets and virtual LANs. They are like high-speed routers without WAN connectivity.

It also acts as a switch because it connects devices on the same IP network or virtual LAN and 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. However, most enterprise networks need high-speed packet processing.

To achieve this, they require high speed using multilayer switches. The Layer 3 switches generally give 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) 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 routers 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 the catalyst 2960 series requires IOS release 12.2(55) or higher to support static routing.

The Catalyst 3560 and 45 series use the Layer 2 interface by default. The catalyst 6500 series uses Layer 3 interfaces by default. So, depending on the switch series, 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” commands in interface mode.