Software Defined Networks Demystified: 5 Truths

Michael Patterson : Advanced NetFlow Traffic Analysis
Michael Patterson
Founder and Product manager for Plixer's Scrutinizer NetFlow and sFlow Analyzer as well as Flow Analytics.

Software Defined Networks Demystified: 5 Truths

For those trying to understand what a Software Defined Network (SDN) is, this post demystifies many of the benefits promised by SDN adversaries.  To do this, I will draw out 5 areas that help you comprehend the truth about where it promises to deliver. First keep in mind that a SDN is broken into two parts: the Control and Data planes.

software defined networks demystified
Few believe that SDNs provide 100% completely new technologies.  It had to derive its features from somewhere however, the difference with an SDN is that it implements features better by being more efficient and easier to manage.  Lets take a look.
  1. Less Expensive: Blah! You can buy a less expensive switch today but, many of us don’t.  This is because we want to invest in a reputable vendor with robust features that help optimize the end user experience and assist with securing the infrastructure.  Often times, vendor specific feature sets are worth the extra money. Who wants an enterprise class switch without flow exporting capabilities, SNMP, VLANs, 802.1X, load balancing, priority queuing or port mirroring?  Sure, you’ll be able to purchase cheap switches to expand your SDN network but, at what cost?
  2. Software Based: Software Defined Networks are no more software based than traditional networking.  This means that we may not have to replace anything.  In some cases, customers will not have to replace existing switches and routers because software upgrades could add the SDN features the business needs.  Network administrators may not even replace the Network Management Station (NMS).  SDN technology is emerging which means that the existing NMS could take on the role of ‘Controller’ in a Software Defined Network. This is especially true if the switches themselves assume much of the forwarding decision logic.
    1. See the YouTube video on “What is a Software Defined Network”.
    2. Spend some time to learn more about the SDN Controller and Data Plane  responsibilities.  
  3. Fault Tolerance: Most of us have had redundancy built in to the architecture for years and we don’t plan on going without it.  How SDNs implement fault tolerance however appears to be an improvement. SDNs claim to maintain better end-to-end visibility into how an outage will impact active connections. When a link goes down, SDNs can intelligently reroute high priority traffic one way and lower priority traffic another in multi-vendor environments.  Some vendor implementations claim to do it instantly. Yes, your network might be able to that today but, will it reroute the traffic 3 or 4 hops back in order to avoid the break and still minimize latency?
  4. Filtering and Security: Your network will witness abnormalities, attacks and insider threats. SDNs do a better job at thinking about security up front as part of the initial configuration.  When suspicious traffic is witnessed, SDNs can reroute or even replicate the traffic to a threat detection appliance for further analysis.  Sure, several vendors can reroute traffic today without SDNs however, in many cases you have to buy 100% into their unique solution. Centralization is another key attribute here.  Imagine a standardized protocol for configuring policies (i.e. ACLs) in a multivendor environment.  This sounds similar to SNMP and MIB-II all over again but, more efficient.  Smart!
  5. More Options: This is probably the most significant of these 5 truths about Software Defined Networks.  The way this technology is playing out, you may only have to invest significantly into the controller.  It is the control plane that claims to deliver much of the intelligence in an SDN but, as stated above, this could likely come at a cost.  If you want to scale the solution because you have a high volume of new connections, you can either purchase more intelligent switches or more controllers. Which will scale better, which will cost more?  If you work in an environment that is at high risk for network based attacks, a more pricey but, intelligent switch may be able to stop the infiltration quicker before it can spread.
Software Defined Networking improves standardization but, just as SNMP and IPFIX offer standard compatibilities across vendors, they also offer support for proprietary feature sets that allow vendors to differentiate themselves. Want to learn more? See the post on “What is a Software Defined Network”.  

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