The Case Against SDN

Andrew Froehlich, Network Engineer & IT Consultant | 2/11/2013 | 5 comments

Andrew Froehlich
Software-defined networks (SDNs) might be a tough sell to both network engineers and CIOs who must choose whether to implement them.

Most IT professionals who gravitate toward a career in networking do so because they like the simplicity of how networks operate. Hardware components, software, and protocols are highly robust, and the network either works or doesn't. There's very little in between. And there's a reason simplicity is built into networking components. If the network is flaky, so is everything riding on top of it.

The SDN concept seems great on paper. It removes intelligence from networking hardware and centralizes it, so it can be managed in a single location. Traffic routing decisions are made at the management plane level and then pushed out to the unintelligent data plane hardware, where routing and switching decisions are executed. This form of intelligence decoupling has already been applied to controller-based wireless infrastructures that leverage dumb access points managed by a centralized server. SDNs build on that concept and take it to the next level.

The primary benefit SDN advocates like to hype is that centralizing traffic routing decisions offers a complete view of the network from end to end. Because of this, reconfigurations can be managed and pushed out networkwide at once, as opposed to making changes one device at a time along the path where traffic flow changes need to be made.

This is all wonderful, but in most enterprise networks, major data flow reconfigurations are few and far between. The need for so much flexibility and control from one end of the network to the other seems unnecessary for most organizations. In fact, many would agree that a great network design is one where very few changes will be required through the life of the hardware.

SDNs go against the "keep it simple, stupid" mantra by which network engineers live and die. Implementing one could destabilize your network for the sake of flexibility -- a benefit that's not widely needed.

I do admit there are some areas where SDNs would be a great success today. Internet and cloud service providers need the type of flexibility that SDNs offer. Because they have customers who are constantly adding, removing, and shifting applications and data, they need the ease of end-to-end management and configuration. Also, as your datacenter becomes more and more virtualized, I can see the use for central control of its network and storage components. But an end-to-end SDN in an enterprise environment? It's simply not needed.

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JohnVerity   The Case Against SDN   5/30/2013 8:32:36 PM
Re: Big Enough to Fail?
SDNs go against the "keep it simple, stupid" mantra by which network engineers live and die.

I disagree. I don;t think there's anything less simple than networks, especially when it comes to reconfiguring them. Someone has compared this task to one of those puzzles we used to play with, with a grid of 16 squares in which 15 tiles could be slid up and down and left and right. Inevitably, moving one tile disrupted the pattern of many others, and trying to fix them created more disruptions. 

The great thing about SDN is that it will rely on a very detailed and maleable model of the network and provide a central control point that will make for much greater and faster flexibility along with much greater security. For once, it will be quite clear what is attached to what.
dilzwilz   The Case Against SDN   2/20/2013 12:38:40 PM
Case Against SDN
I like your point regarding good network design; how good design, in essence thwarts the need to redesign in order to accomodate future network traffic. Don't get me wrong, for I love the idea of "if it aint broke, you're not looking hard enough", and re-engineering, But I also tend to think that ideas like SDN are born out of 1. not understanding a [in this case, Networking] technology, design, protocols, and everything else associated with it ..and therefore 2. trivializing the importance of not modifying the infrastructure everytime there's some project or development. Rather,  the network guru can answer the project's needs by creating a VLAN [for instance], or something. 3. the resentment of having to deal with the guru "everytime we want to do something". "Can't somebody come up with a new way to do networking? Can't the software guys make up a way to change the network?"
Andrew Froehlich   The Case Against SDN   2/12/2013 9:42:52 PM
Re: Big Enough to Fail?
SDNs are less reliable for two reasons. First, the technology is still untested. There's likely bugs that will need to be worked out. Second, there won't be many network professionals that are well versed in SDN management. Both can and will be overcome...but it will take time.
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David Wagner   The Case Against SDN   2/11/2013 11:58:54 AM
Re: Big Enough to Fail?
Also, Andrew. I remember when a similar argument was made about server virtualization. Only big enterprises needed it was the mantra, but clearly that wasn't the case. Is this just a short term issue and we're all going to be using SDN soon?
David Wagner   The Case Against SDN   2/11/2013 11:57:57 AM
Big Enough to Fail?
Interestingly enough, it seems like you are saying that really big networks need SDN, but that SDN is less reliable. Is it safe ot say then that the bigger th network the less reliable it is anyway and SDN will help with that problem? But that smaller networks don't need it?


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