In this section, we will explore the most well-known L2 feature, which is VLAN. VLAN or L2 isolation, is one of the most basic features of every Ethernet switch. For those of you who are not familiar with the VLAN concept, in simple terms, it means dividing an Ethernet switch into smaller isolated switches that do not communicate with each other. This is mostly done in the switch ASIC (main switch hardware chipset), and it does not require the processing power of a switch CPU (Switch CPU is where the switch operating system runs). Normally, ASIC partitions the internal CAM table and assigns specific ports to the partitions; this results in full isolation of the ports assigned to different VLANs in a switch.
In a pure SDN world, as we have learned, we only have flow tables and the OpenFlow agent. Switch doesn't have the feature to create VLANs; therefore, it is the SDN controller's job to translate the VLAN function into a flow table.