This document introduces software-defined networking (SDN) and why it is important. It discusses how SDN separates the network control plane from the forwarding plane, allowing for more programmable networks. This benefits researchers developing new network architectures and cloud computing environments seeking scalable, cost-effective data center networks. The document also covers how network functions can be virtualized and run on general hardware rather than dedicated devices, and outlines some key SDN concepts including the "dumb fabric, smart edge" architecture and opportunities for new performance measurement tools.

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Software-Defined Networking
Simon Leinen
Team Leader, Peta Solutions
simon.leinen@switch.ch
eduPERT Performance U! 2013-03-07

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What is SDN
and why should I care?
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Why SDN?
• Networking software-defined anyway?
• Well yes, but… (is that of any use to us?)
– Vertical integration dominates: Hardware, OS,
“applications” all in a (closed) box
– Network-wide functions defined by protocols
Results:
• Resistance to innovation (“fossilization”)
• Cost/performance issues
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Drivers towards SDN
• Researchers who want to “innovate”
– Future Internet/”Clean Slate” initiatives
• “Warehouse-scale computing” (Cloud)
– Need to build scalable, cost-effective fabrics
– Research shows it can be done (VL2,
Portland etc.) using fat trees/leaf+spine and
multipath load balancing (e.g. Valiant) at edge
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Data Center Networks
5Source: “A simpler data center fabric emerges”, Lippis White Paper

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Data Center Networks
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Source: A simpler data center fabric emerges, Lippis White Paper

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Leaf-spine traffic flow (multipath)
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Source: Interop 2012 talk by Brad Hedlund
Architecting Data Center Networks…

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“Mainframe business model”
8J. Hamilton, “Data Center Networks Are In My Way”, October 2010

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Possible Approaches
• Separate forwarding/packet processing
logic (data plane) and control plane
– OpenFlow (Kurt’s talk)
• Improve onboard programmability
– SDKs, better access to embedded OS
• Use general-purpose hardware
– E.g. Linux/Intel servers (Luke’s talk)
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Dumb Fabric/Smart Edge
Some SDN proponents suggest this
architecture for future (DC) networks:
• Use a simple fabric for bottleneck-free bw.
– Could be IP, MPLS, or OpenFlow net…
• Implement functionality at edge
– E.g. isolation, load distribution over multipath
– E.g. in the CPU-based hypervisor
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NFV (Network Function Virtualization)
• Telco buzzword for something natural…
• “Network functions” can be run in VMs
• This is already happening:
– Cisco Nexus 1000V
– Cisco Cloud Services Router 1000V
– Juniper vGW (Virtual Gateway) firewall
• Note how “hardware-based” firewalls are
superseded by Xeon-based ones
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Industry taking SDN seriously?
• 2012-04-17: U. Hölzle gives talk @ONS
about production Google OpenFlow WAN
• 2012-07-23: VMware acquires Nicira for
USD 1.05 billion
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Do we have to take it seriously?
• If you’re an SDN researcher, yes 
• If you’re a backbone operator… not yet(?)
• If you have to do with campus networks
and edge network devices (firewalls etc.):
yes
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What about Performance?
• New approaches to fast networks:
massive multipath, stupid core, edge
functions on CPUs
• New requirements and new opportunities
for instrumentation (measurements)
• New opportunities for things to go wrong,
e.g. OpenFlow table-update bottlenecks
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Further Reading
• Gentle Introduction to SDN, S. Shenker, 2012
http://www.youtube.com/watch?v=eXsCQdshMr4
• Datacenter Networks Are In My Way, J.
Hamilton, 2010 (read the
slides!)http://perspectives.mvdirona.com/2010/10/31/Datacenter
NetworksAreInMyWay.aspx
• OpenFlow @Google, U. Hölzle, 2012
http://www.youtube.com/watch?v=VLHJUfgxEO4
• The Future of Networking, and the Past of
Protocols, S. Shenker, 2011
http://www.youtube.com/watch?v=YHeyuD89n1Y
http://www.slideshare.net/martin_casado/sdn-abstractions
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Further Further Reading
• Open Networking Summit (industry)
– Each April in Silicon Valley
• HotSDN workshop (research)
– Each Summer wherever SIGCOMM is held
• SDN MOOC by Nick Feamster (Georgia
Tech.) – 6 weeks starting on 27 May
https://www.coursera.org/course/sdn?goback=.gde_4359316_memb
er_207551682
• Meta-list: http://www.nec-labs.com/~lume/sdn-reading-list.html
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