Category: OpenFlow

It’s easy to say “SDN is the physical separation of the network control plane from the forwarding plane, and where a control plane controls several devices,” handwave over the details, and let someone else figure them out. Implementing that concept in a reliable manner is a totally different undertaking.

Even though I questioned the wisdom of writing your own network programming applications, I know I would immediately jump into those waters if I were 20 years younger. If you’re like my younger self, you might want to keep a few guidelines in mind.

Major vendors (with the exception of NEC) haven’t made any progress. Juniper still hasn’t delivered on its promises. Cisco still hasn’t shipped an OpenFlow switch or an SDN controller (although they’ve announced both months ago). Brocade supposedly has OpenFlow on their high-end routers and Arista supports OpenFlow on its old high-end switch (but not in GA EOS release).

Every major vendor is talking about SDN, but it’s mostly SDN-washing (aka CLI-in-API-disguise). Cisco is talking about OnePK, and has shipping early adopter SDK kit, but it will take a while before we see OnePK in GA code on a widespread platform.

Startups aren’t doing any better. Big Switch is treading water and trying to find a useful use case for their controller. Nicira was acquired by VMware and is moving away from OpenFlow. Contrail was acquired by Juniper and recently shipped its product (which has nothing to do with OpenFlow and not much with SDN). LineRate Systems was acquired by F5 and disappeared.

We haven’t seen customer deployments either. Facebook is doing interesting things (but from what I’ve heard they’re not OpenFlow-based), Google has an OpenFlow/SDN deployment, but they could have done the exact same thing with classical routers and PCEP, Microsoft’s SDN is based on BGP (and works fine).

It seems like the reality hit OpenFlow and it was a very hard hit… and according to Gartner we haven’t reached the trough of disillusionment yet.

If you repeat something often enough, it becomes a “fact” (or an urban myth). SDN is no exception, industry press loves to explain SDN like this:

[SDN] takes the high-end features built into routers and switches and puts them into software that can run on cheaper hardware. Corporations still need to buy routers and switches, but they can buy fewer of them and cheaper ones.

That nice soundbite contains at least one stupidity per sentence:

The number of OpenFlow flows you can use in hardware switches is one of the major roadblocks in a large-scale OpenFlow deployment. Vendors often use hardware TCAM tables to match OpenFlow entries, and as those tables are expensive to implement in silicon, they tend to be small. Typical TCAM tables have a few thousand entries.

Is that good enough? As always, the answer depends on the use case, the network size, and implementation details. This blog post will focus on the last part.

TL&DR summary: Use switches that support OpenFlow 1.3.

OpenFlow is a simple TCAM programming protocol, and can be used to implement any network forwarding paradigm as long as:

• OpenFlow specifications include matches and actions (including rewrites) of the packet header fields used in the forwarding paradigm. For example, you cannot program SRv6 tunnels with OpenFlow because it’s not part of OpenFlow standard.
• The forwarding hardware you want to use supports the OpenFlow matches and actions you need in your forwarding paradigm.
• The forwarding paradigm does not use dynamic interfaces (example: MPLS-TE tunnels) or multipoint tunnel interfaces (example: VXLAN). OpenFlow was designed to be used on point-to-point physical interfaces and does not include interface management.

This blog post describes some of the more common OpenFlow use cases (assuming you want to use an obsolete rarely-implemented protocol).

My keynote speech @ PLNOG11 conference was focused on (surprise, surprise) overlay virtual networks and described the usual motley crew: The Annoying Problem, The Hated VLAN, The Overlay Unicorn, The Control-Plane Wisdom and The Ever-Skeptic Use Case. You can view the presentation on my web site; PLNOG organizers promised video recording in mid-October.

Just in case you’re wondering why I keep coming back to PLNOG: they’re not only as good as ever; they’re getting even more creative.

Fast advances in networking technologies (and the pixie dust sprinkled on them) blinded us – we lost our gut feeling and rule-of-thumb. Guess what, contrary to what we love to believe, networking isn’t unique. Physicists faced the same challenge for a long time; one of them was so good that they named the whole problem category after him.

Every time someone tries to tell you what your problem is, and how their wonderful new gizmo will solve it, it’s time for another Fermi estimate.

When talking about OpenFlow and the whole idea of controller-based networking, people usually say “well, it’s nothing radically new, we’ve been using wireless controllers for years and they work well, so the OpenFlow ones will work as well.”

Unfortunately, the comparison is totally misleading.

In the previous posts I described how a typical overlay virtual networking data plane works and what technologies vendors use to implement the associated control plane that maps VM MAC addresses to transport IP addresses. Now let’s walk through the details of a particular implementation: Nicira Network Virtualization Platform (NVP), part of VMware NSX.

Every single network device (or a distributed system like QFabric) has to perform at least three distinct activities:

• Process the transit traffic (that’s why we buy them) in the data plane;
• Figure out what’s going on around it with the control plane protocols;
• Interact with its owner (or NMS) through the management plane.

Routers are used as a typical example in every text describing the three planes of operation, so let’s stick to this time-honored tradition:

The last part of the ProgrammableFlow webinar described typical use cases including Cloud-as-an-Appliance, traffic steering (used by appliances like Radware DefenseFlow) and hypervisor switching with PF1000. Predictably, the use cases were followed by a lengthy Q&A session.

NEC and a slew of its partners demonstrated an interesting next step in the SDN saga @ Interop Las Vegas 2013: multi-vendor SDN applications. Load balancing, orchestration and security solutions from A10, Silver Peak, Red Hat and Radware were happily cooperating with ProgrammableFlow controller.

A curious mind obviously wants to know what’s behind the scenes. Masterpieces of engineering? Large integration projects ... or is it just a smart application of API glue? In most cases, it’s the latter. Let’s look at the ProgrammableFlow – Radware integration.

The true OpenFlow zealots would love you to believe that you can drop whatever you’ve been doing before and replace it with a clean-slate solution using dumbest (and cheapest) possible switches and OpenFlow controllers.

In real world, your shiny new network has to communicate with the outside world … or you could take the approach most controller vendors did, decide to pretend STP is irrelevant, and ask people to configure static LAGs because you’re also not supporting LACP.

Brent Salisbury sent me a link to a fantastic OpenFlow/SDN presentation Scott Shenker did @ Stanford University a few days ago. It’s a perfect introduction to the fundamental ideas behind SDN and therefore a must-see for everyone vaguely involved in networking.

Here are some of the highlights (from my highly biased perspective):