In networking, as in life, we often use the same terms to mean many different things. One of the biggest culprits of this in networking is “edge.” An edge device is usually considered to be a device that connects into a network in only one place. Traffic can flow from an edge device, or it can flow to an edge device, but it can never, ever flow through an edge device. I say never—that’s not entirely true, but I’ll get back to that later. In a campus network, the edge devices are things like users’ computers, laptops, and printers; mobile phones; and tablets.
In data centers, the end devices are servers or, more than likely in the SDDC, virtual machines, or possibly containers. The exception to the rule about traffic not flowing through an edge device is the “edge router,” which more often than not takes the form of a firewall: a perimeter firewall. If we consider north/south versus east/west traffic flows, north/south traffic flows move between the edge and the core, and east/west circumnavigates the network, to take the globe analogy a step further. This distinction becomes important as we look at the direction that networking has taken, and the direction I believe it will continue to take.