Wednesday, June 25, 2014

Riding the SDN Hype Wave

In case you haven't noticed, Software-Defined Networking has become the guiding meme for most innovation in networks over the past few years.  It's a great meme because it sounds cool and slightly mysterious.  The notion was certainly inspired by Software-Defined Radio, which had a relatively well-defined meaning, and has since spread to other areas such as Software-Defined Storage and, coming soon, the Software-Defined Economy.
As a networking veteran who has fought in the OSI and ATM wars, I like making fun of these fads like the next person—buzzword bingo anyone? But actually, I consider the SDN hype a really good thing.  Why? Because, to quote Cisco CTO Padmasree Warrior, "networking is cool again", and that's not just good for her company but a breath of fresh air for the industry as a whole.
What I like in particular is that SDN (because nobody knows exactly what it means and where its limits are...) legitimates ideas that would have quickly been rejected before ("it has been known for years that this doesn't scale/that this-and-that needs to be done in hardware/...").  Of course this also means that many tired ideas will get another chance by being rebranded as SDN, but personally I think that this does less damage.

SDN Beyond OpenFlow

The public perception of SDN has been pretty much driven by OpenFlow's vision of separating forwarding plane (the "hardware" function) and control plane, and using external software to drive networks, usually using a "logically centralized" control approach.
The Open Networking Forum attempts to codify this close association of SDN and OpenFlow by publishing their own SDN definition.  OpenFlow has huge merits as a concrete proposal that can be (and is) implemented and used in real systems.  Therefore it deserves a lot of credit for making people take the "SDN" vision seriously.  But I think the SDN meme is too beautiful to be left confined to OpenFlow-based and "logically centralized" approaches.  I much prefer JR Rivers's (Cumulus Networks) suggestion for what SDN should be: "How can I write software to do things that used to be super hard and do them super easy?" That's certainly more inclusive!

x86 as a Viable High-Speed Packet Processing Platform

Something that I definitely consider an SDN approach is to revisit generic computing hardware (mostly defined as "x86" these days) and see what you can do in terms of interesting packet processing on such platforms.  It turns out that these boxes have come a long way over the past few years! In particular, recent Intel server CPUs (Sandy Bridge/Ivy Bridge) have massively increased memory bandwidth compared to previous generations, CPU cores to spare.  On the interface front, most/all of today's 10 Gigabit Ethernet adapters have many helpful performance features such as multiple receive/transmit queues, segmentation offload, hardware virtualization support and so on.  So is it now possible to do line-rate 10Gb/s packet processing on this platform?
The dirty secret is that even the leading companies in ASIC-based backbone routers are already using regular multi-core CPUs for high-performance middleboxes such as firewalls (as opposed to previous generations that had to use expensive-to-design and program network processors, FPGAs and/or ASICs).
Intel has its DPDK (Data Plane Development Kit) to support high-performance applications using their network adapters and processors, and there are several existence proofs now that you can do interesting packet processing on multiple 10Gb/s interfaces using one core or less per interface—and you can get many of those cores in fairly inexpensive boxes.

Snabb Switch

One of my favorite projects in this space is Luke Gorrie's Snabb Switch.  If CPU-based forwarding approaches are at the fringe of SDN, Snabb Switch is at the fringe of CPU-based forwarding approaches... hm, maybe I just like being different.
Snabb Switch is based on the Lua scripting language and on the excellent LuaJIT implementation.  It runs entirely in user space, which means that it can avoid all user/kernel interface issues that make high-performance difficult, but also means that it has to implement its own device drivers in user space! Fortunately Lua is a much friendlier platform for developing those, and one of Luke's not-so-secret missions for Snabb is that "writing device drivers should be fun again".
The Snabb Switch project has gained of traction over the year or so since its inception.  A large operator is investigating its use in an ambitious backbone/NFV project; high-performance integration with the QEMU/KVM hypervisor has been upstreamed; and the integration into OpenStack Networking is making good progress, with some hope of significant parts being integrated for the "Juno" release.  And my colleague and long-time backbone engineering teammate Alex Gall is developing a standalone L2VPN (Ethernet over IPv6) appliance based on Snabb Switch, with the ultimate goal of removing our only business requirement for MPLS in the backbone.  Now that should convince even the curmudgeons who fought in the X.25 wars, no?
The final proof that Snabb Switch's world domination is inevitable is that it was featured in the pilot episode of Ivan Pepelnjaks new Software Gone Wild podcast.
(In fact that is the very reason for this post, because yours truly also had a (small) appearance in that episode, and I had to give up the address of my blog... and now I'm afraid that some of the venerable readers of Ivan's blog will follow the link and find that nothing has been posted here lately, even less so related to networking.  Welcome anyway!)

Come on in, the water's fine!

So turn your bullshit detectors way down, embrace the hype, and enjoy the ride! There are plenty of good ideas waiting to be implemented once we free ourselves from the rule of those ASIC-wielding vertically integrated giga-companies...
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