When we look at network switch specifications, we tend to fixate on the numbers for the front of the box. Switches are sold on the basis of how many ports of a particular speed they make available to the network. It's easy to understand why we do this, but it gives a picture of the switch that is, at best, incomplete. At worst, the picture we get is misleading, and advancing technology could make the picture even less accurate.
We should spare some time to look at the switch fabric to understand what a switch can really do for the network.
What is the switch fabric?
At its simplest, the switch fabric is the backplane that connects all of the ports into a single network appliance. You would think you need a backplane within the switch that is at least equal in speed to the total of the ports on the front. In reality, the total bandwidth of the backplane is often less than the aggregate of the front panel.
Just as the CPU in your workstation spends much of its time waiting for something to happen, your network switch spends most of its time passing no packets at all. So you want to look at the fabric in the context of your applications and organization. If your business is built around streaming video, then the fabric will need to be far more robust than if your company is mostly about email.
Why you should pay attention to software-defined networks
All of this changes when you have a high demand network and multiple switches. Now, the backplanes of all the switches together form the network fabric. You'll want to make sure that the vendor you choose has management software that manages the aggregation of the network switches as a single fabric. The ultimate form of that management comes in software-defined networks (SDN). While today SDN is seen primarily in ISPs and large-enterprise networking, rapidly building capabilities and rapidly lowering costs mean that you should pay attention as you're planning your next network.
SDN automates the rapid reconfiguration of network switches to meet the changing needs of a business application environment filled with virtual servers and storage. One of the keys to making this possible is control software that treats the network fabric as distinct from the front-panel ports. The big thing to know at this stage of market development is that you should ask the vendor whether its switches are SDN ready and whether the SDN software is compatible with open-source standards like Open Flow or is based entirely on proprietary technology.
Choosing network switches based solely on the ports lining the front of the switch can be fast and simple, but it will also keep your switches from growing with your business and keeping up with technology. Pay attention to the network fabric within and among the switches, and you'll be prepared for the network to add value to your total application infrastructure.