Layer 2, Layer 3 FAQs

What is meant by “Layer 2 and Layer 3”?

Networks have been built for 30 years using two basic principles; 1) Switching in the Local Area Network, usually within a single data center, and 2) Routing to handle the scale and expansion from one physical location to include additional geographically dispersed. Switching is many times referred to as “Layer 2” while “Routing” can be referred to as “Layer 3”. Years ago, those two functions existed in entirely different appliances, but over the years many vendors have combined those functions into a single device. Speed and distance delineations have blurred. That said, what still characterizes Layer 2 is a set of local area network (LAN) protocols which were intended to span high-speed media such as Ethernet, and Layer 3 refers to the means to connect LANs over wide-area networks. Popular Layer 2 protocols include Spanning-Tree (STP), Link-Aggregation (LAG) and Virtual LANs (VLAN). Popular Layer 3 protocols include Open Shortest Path First (OSPF), Border-Gateway Protocol (BGP) and Virtual Router Redundancy (VRRP).

Why does support for Layer 2 and Layer 3 matter in the context of SDN?

It is the support of these protocols that defines the ability for any new device to participate within an existing production network. As a general rule, the more of these protocols that are supported, the more compatible any device is. This is particularly important in the context of SDN as many of the industry’s SDN offerings have limited or no support for existing environments. It is the specific support for these Layer 2 and Layer 3 protocols that enables migrations from older topologies to newer SDN deployments. Compatibility is defined by how complete an SDN offering supports these protocols.

How can SDN and Layer 2 and Layer 3 exist at the same time?

The Pluribus approach to SDN is very different from the other offerings in this space. Using standard cluster technologies running across existing Layer 2 and Layer 3 networking transports, the Pluribus Virtualization-Centric Fabric (VCF™) solution allows all Pluribus-powered switches to become aware of each other’s configuration and operating tables. The result is that each switch’s controller contains an identical superset of operating tables, made up of content derived from each of the other switches. Layer 2 and Layer 3 protocols are used to cluster these switches’ controllers to allow them to share these operating tables, and ultimately to move packets across the entire structure to their specific destination. Pluribus VCF is based upon Layer 2 and Layer 3 only, without the need to introduce ANY vendor-specific nor SDN-specific protocols.

What happens if I choose an SDN solution does not support Layer 2 and Layer 3?

Without the comprehensive support of Layer 2 and Layer 3, the resulting deployment becomes an island of computing. The switches and all of the attached server and storage devices can easily communicate with one another, but they become invisible to the rest of the organization’s infrastructure. Without Layer 2 and Layer 3 support, the new SDN structure has the appearance of being disconnected from the rest of IT.