Category: SDN

Got this set of questions from a CCIE pondering emerging technologies that could be of potential use in his data center:

I don’t think OpenFlow is clearly defined yet. Is it a protocol? A model for Control plane – Forwarding plane FP interaction? An abstraction of the forwarding-plane? An automation technology? Is it a virtualization technology? I don’t think there is consensus on these things yet.

OpenFlow is very well defined. It’s a control plane (controller) – data plane (switch) protocol that allows control plane to:

I read two great blog posts on Sunday: evergreen Fallacies of Distributed Computing from Bob Plankers and forward-looking Understanding Hadoop Clusters and the Network from Brad Hedlund. Read them both before continuing (they are both great reads) and try to figure out why I’m mentioning them in the same sentence (no, it’s not the fact that Hadoop uses distributed computing).

Frequent eruptions of OpenFlow-related hype (example: Being Open about Virtualization and Cloud Interoperability published after Brocade Technology Day Summit) call for a continuous myth-busting efforts. Let’s start with a widely-quoted (and immediately glossed-over) fact from Professor Scott Shenker, a founding board member of the Open Networking Foundation: “[OpenFlow] doesn’t let you do anything you couldn’t do on a network before.”

To understand his statement, remember that OpenFlow is nothing more than a standardized version of communication protocol between control and data plane. It does not define a radically new architecture, it does not solve distributed or virtualized networking challenges and it does not create new APIs that the applications could use. The only thing it provides is the exchange of TCAM (flow) data between a controller and one or more switches.

Earlier this month I wrote “we’ll probably have to wait at least a few years before we’ll see a full-blown hardware product implementing OpenFlow 1.1.” (and probably repeated something along the same lines in during the OpenFlow Packet Pushers podcast). I was wrong (and I won’t split hairs and claim that an academic proof-of-concept doesn’t count). Here it is: @nbk1 pointed me to a 100 Gbps switch implementing the latest-and-greatest OpenFlow 1.1.

Network World has published another masterpiece last week: FAQ: What is OpenFlow and why is it needed? Following the physics-changing promises made during the Open Network Foundation launch, one would hope to get some straight facts; obviously things don’t work that way. Let’s walk through some of the points. While most of them might not be too incorrect from an oversimplified perspective, they do over-hype a potentially useful technology way out of proportions.

NW: “OpenFlow is a programmable network protocol designed to manage and direct traffic among routers and switches from various vendors.” This one is just a tad misleading. OpenFlow is actually a protocol that allows a controller to download forwarding tables into one or more switches. Whether that manages or directs traffic depends on what controller is programmed to do.

Last week Greg (@etherealmind) Ferro invited me to the OpenFlow Packet Pushers podcast with Matt Davey. I was pleasantly surprised by Matt’s realistic attitude (you should really listen to the whole podcast), it was nice to hear that they’re running a country-wide pilot with OpenFlow-enabled switches deployed at several universities, and some of the applications he mentioned (for example, the capability to download ACLs into the switch from your customized application) definitely tickled my inner geek. However, I’m even more convinced that the brouhaha surrounding Open Networking Foundation has little grounds in the realities of OpenFlow.

A typical networking device (bridge, router, switch, LSR …) has control and data plane. The control plane runs all the control protocols (including port aggregation, STP, TRILL, MAC address learning and routing protocols) and downloads the forwarding instructions into the data plane structures, which can be simple lookup tables or specialized hardware (hash tables or TCAMs).