Beginners guide to Software Defined Networking (SDN)

One of the hot topics at IPExpo London this year has been the rise of SDN, an emerging architecture that’s got the potential to deliver a huge paradigm shift in the industry but what’s it all about and why does it matter?

The problem with current network architecture is that we’ve managed to acheive great flexibility from both the server farms (through virtualisation) and the delivery capacity through scalable delivery controllers like NetScaler but the typical data centre network (the bit that connects the two together) is, to coin a phrase, the weakest link.

Let’s take my journey in to IPExpo as an example of the concept.

My usual route is by train from the village to the nearby town where I swap to a mainline service into the capital. In west London, I change again on to the underground and eventually get to the venue. I’ve tried different routes in the past but this one looks to be the best so I stick with it as it usually works.

After purchasing a ticket from the friendly man at the station I got on the train in the village, sat in my usual seat and caught up with a few mails on the short journey to the mainline. The conductor doesn’t ask to see my ticket anymore as he recognises me but always says ‘Good morning’ as he continues down the aisle. To me this is great service.

As we pull in to the mainline station, things don’t look good. There’s well over 200 people waiting for the mainline train which is running around 5 mins late. When it finally arrives, it’s packed. Approximately 20 people got off and all 200 of us on the platform tried to get on which was never going to happen so I had to wait for the next one which wasn’t quite so busy but I still had to stand by the door as all the seats (and the isles) were full. Service levels are slipping….

As the train pulls out of the station, an announcement is made by the driver that due to an earlier incident, the route is congested and we will be delayed further. I’ve been here more than once before and have come to the conclusion that there’s nothing I can do about it but a family stood close by who are traveling to the airport are getting very stressed!

Eventually we arrive at the next stop on my route where I change to the Underground. I know exactly where I’m going and how to get there on the District line but due to flooding at one of the stations I find myself opening a tube map on my phone to come up with an alternative route. I’ve now got three choices, all of which look pretty similar but decide on the Central line to Notting Hill Gate, swap to the District line southbound for one stop and I finally make it to IPExpo. Late.

Reading that back to myself sounds like fiction but anyone who uses the train/tube network on a regular basis knows that service levels can fluctuate wildly and the same applies to networks in data centres.

In data centre networks, we build fixed paths for traffic to follow, similar to the train tracks. We provision capacity based on the anticipated volume of users (the number of carriages & frequency of the trains) and when things don’t go to plan we often need to manually come up with a ‘plan B’ which may or may not deliver us to our destinations in an acceptable timeframe. There must be a better way.

What if the rail & tube network had a bit more intelligence? Had the ability to recognise me and where I wanted to go? To deliver me to my destination via the fastest possible route with no delays? To automatically find the best alternative route when problems occur? Better still if there was a mechanism that recognised the number of people waiting at the platform and actually added capacity (more carriages) to each train when the demand dictated. How about if that intelligence also had the ability to remove capacity when the demand subsides so that there was just the right amount of carriages with just the right amount of seats at each station? And what would be even better would be the ability for the trains to be available when I step on to the platform rather than having to follow the timetable? Would that be great service?

As a concept, Software Defined Networking provides exactly this kind of methodology. In current environments, applications are deployed on servers and network engineers define a fixed mechanism of capacity and route to deliver the best service possible. Changes can be time consuming and service levels can only be maintained by providing enough capacity to handle peak traffic amounts. When user counts are low, the network is massively over provisioned, if user counts get too high the network can’t cope and service levels drop. It’s back to the old capacity vs cost conversations…

SDN introduces intelligence in to the network to allow it to dynamically make changes to the infrastructure configuration as the demand dictates. As user counts peak, it can increase capacity to enable service levels to be maintained and more importantly has the ability to reduce consumption of resource when the demand subsides to allow maximum efficiency. SDN has the ability to recognise new application servers and dynamically make changes to the configuration of traffic paths to automate the process of getting the users to the server, reducing the deployment time and configuration cost. In short, the software defines what the network looks like and how it should be configured.

Server virtualisation has introduced flexibility & efficiency in to the ‘back end’ infrastructure. Scalable, feature rich application delivery controllers such as NetScaler bring the same benefits to the ‘front end’ delivery mechanism. SDN is still an emerging technology but the ability bring these elastic capabilities to the bit that connects the servers to the delivery mechanism (the network itself) has been the basis of some very interesting conversations at IPExpo this year…I’ll let you know how the deployments go…!

Clearly, SDN is still in its infancy and requires vendors to get away from the greedy proprietary models of old. For SDN to work, vendors need to embrace a collaborative, open, service first based approach to their customers. The recent expansion of the strategic partnership agreement between Citrix & Cisco gives a taste of what’s to come – immensely capable vendors aligning roadmaps to become greater than the sum of their parts. I’ll be posting about the new NetScaler SDX Ready messaging shortly but when you add the likes of Palo Alto, Websense & BlueCat it’s possible to start to see how Software Defined Networking has the ability to deliver new levels of service and efficiency to millions of users all over the world…

So what’s it to be, great service & maximum efficiency….or leaves on the line?! Al

© Al Taylor 21st Oct 2012

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About netscalertaylor

Co-founder at cloudDNA - a team of like minded Citrix NetScaler specilists

3 responses to “Beginners guide to Software Defined Networking (SDN)”

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