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Q&A: Big Switch SDN

Got this set of questions from one of my readers:

I just met up with DELL guys for Big Switch SDN. They claim there is no routing running on leaf switches, the BCF is purely OpenFlow.

Almost true. It is based on OpenFlow, but they use tons of their own OpenFlow extensions to get stuff to work. That’s also why you have to install their agent on the switches.

Want to hear your idea how they can handle network partitions?

They can’t (at least not to the same extent the SDN solutions that don't have centralized control plane like Cisco ACI can). They have a “headless mode” where the network keeps forwarding stuff even when the switches lose connectivity to all controllers, but the moment you have a topology change, which can be as simple as a VM (and thus MAC/IP) move, you’re toast.

In theory, you could cope with core link failures in headless mode if (A) the switches run some link quality monitoring mechanism (example: BFD) and (B) the controller pre-programs backup paths into the switches. There’s no way to cope with external changes without access to a proper control plane.

I think the leaf switch do not have any control-plane.

Somewhat correct. They have ARP and LACP offloads, and they’re probably running BFD on the core links, so at least these things continue to work when the controller is not reachable.

You’ll find a few more details in the SDN Use Cases webinar (I spent ~15 minutes explaining BCF), and if you’re interested in designing more down-to-earth data center infrastructure, check out my online course.


  1. van,
    When I look at and or sdncentral I see SO many many vendors. Is there that much of "SDN" buy in happening ie in terms of business? All of them seem to have active customer use cases etc...What am I missing? Second question (more of a comment) is not matter how smart, organized or resourceful, I doubt anyone has the ability to compare contrast so many. Is there that big of a gap with current supply and demand (of features I guess) that justifies this? For context sake, I'm at a VAR in NYC, in the industry for 25+ years, technical, have attended a lot of your SDN seminars incl one in Miami(maybe I was on a bio break when you may have been explaining this madness) by no means a novice. This just intrigues me.

  2. Short answer: No. Most of that is marketing and posturing. Like with ATM in the old days, most of SDN is still a zero trillion dollar business.

    I know of several NSO deployments and a few NSX and ACI deployments. Supposedly people are deploying Contrail, Nuage VSP and SD-WAN. Beyond that? Not really.


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