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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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