Tag Archives: nvos

Of Controllers and Why Nicira had to do a deal (Part III: SDN And Openflow – Enabling Network Virtualization in the Cloud)

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The challenges faced by Openflow and SDN

This is the 3rd and final article in this series (Click for Part I and Part II). As promised, let’s look at some of the challenges facing this space and how we are addressing those challenges. In the process, we also look at the role of controllers in a network fabric in more detail in this post.

Challenge 1 – Which is why Nicira had to get a big partner

I see plenty of articles talking about Nicira being aquired. But there’s one question that no one seems to be asking – that if the space is so hot, why did Nicira do the deal so early? The deal size (1.26B) is not chump change but if I were them and my stock was rising, I would have held off to continue pushing to change the world. So what was the rush? I believe the answer lies in some of the issues I discussed in Part II of this series – in the difference between a server-based and switch based approach! The Nicira solution was very dependent on the server and the server hypervisor. The world of server operating systems and hypervisors is so fragmented today, that staying independent would have been a very uphill battle for them. So tying up with one of the biggest hypervisors made sense for them. I believe they did the smart thing to ensure that the technology can keep moving forward. Undoubtedly, VMware is a good, technology-driven company. The moot question now is how long before the VMware/EMC and Cisco relationship comes unhinged?

Challenge 2 – Why Controllers? Or the divide between Control Plane and Data Plane

The current promise of having a standard way of controlling networking and a controller that is platform independent is huge. It provides simplified network management and rapid scale for virtual networks. Yet, the current implementations have become problematic.

Since the switches are dumb and do not have a global view, the current controllers have turned into a policy enforcement engine as well. New flow setup requires a controller to agree which means that every flow now needs to go through the controller which in turn instantiates them on the switch. This, however, raises several issues:

  • A controller which is essentially an application running on a server OS over a 10gbs link (with a latency of tens of milli-seconds) is in-charge of controlling a switch which, in turn could be switching 1.2 Tbps of traffic at an average latency of under a μs and dealing with 100k flows with ~30% of them being setup or torn down every second. To put things in perspective, a controller takes tens of milliseconds to set up a flow while the life of a flow transferring a 10Mb data (typical web page) is 10 msec!!
  • To deal with 100k flows, the switch ASICs need to have that kind of flow capability. The current (and coming generation) of ASICs have no where near such capability so one can only use the flow table as a cache. This brings to us the 3rd issue.
  • Flow setup rate is anemic at best on the existing hardware. You are lucky if you can get 1000 flows per second.

So what is lacking is a Network Operating system on the switch to support the Controller App. If you look at the server world, the administrator specifies the policies and it’s the job of the OS (that works very closely with the Hardware) to enforce these policies. In the current scenario, it seems like an application running on bare metal with no Operating system support. Since this is a highly specialized application, it needs a specialized Operating system – or, a Network Operating system which can also be virtualized.

Challenge 3 – The Controller based Network

For a while, people were just tried to their inflexible networks which didn’t see any innovation in last two decades while the server and storage went through major metamorphosis. That frustration gave birth to Openflow/SDN which has currently morphed into a controller mania. Moving the brain from body and separating them creates somewhat of a split brain problem since the body (or switch in this case) still needs somewhat of a brain. What we need is a solution that encompasses the entire L2 fabric and the controller and Fabric work as one while providing easy abstractions for user to achieve their virtualization, SLA and monitoring needs.

A Distributed Network Hypervisor or Netvisor to the rescue

So what we (at Pluribus) saw early on is that the world of servers is a very good example. The commoditization of ASICs and value moving to software is pretty much what’s happening in the world of storage and is bound to happen in the world of networking. So we decided to do things in the right order i.e. get the bleeding edge commodity ASICs and create a Network Operating System with the following properties:

  • Network OS – Designed to manage  these ASICs which are very specialized and powerful.
  • Distributed – Networks have more than one switch, working in tandem to support end-to-end flow.
  • Virtualized – Ability to run both Physical and Virtual Networking applications. As I mentioned before, the switch is not the network. We need to deal with all network services in physical and virtual form and the network OS needs to support that.

Hence we created a Distributed Network Hypervisor called Netvisor™ (a key component of the nvOS™ operating system) or nvOS™. It is designed to run on the network switches and supports both physical and virtual network services. It also runs a controller where the controller is a policy distribution engine and no longer a policy enforcement engine.

 

As shown in the left half of the above figure, the current dividing line between the control plane and data place is not going to scale and perform. The line we originally drew (and the founding principle of Pluribus Networks), as shown in the right-half, needs to be delivered for SDN and Openflow to deliver its true promise.

SDN and Openflow- Enabling Network Virtualization in the Cloud: Part II

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Using Openflow – state of the ART

In an earlier article, we discussed the components of Openflow and building blocks of a Software Defined Network. In this part, we’ll discuss some interesting things being done today to make it all work. However, before we do that, it’d be worthwhile to first discuss the concept or definition of a flow and why is it important.

 

What is a Flow and the split between Hardware and Software

A flow is a simple mechanism to identify a group of packets on the wire. So a packet coming from a particular machine can be identified by the machine’s MAC or IP address which appears as source MAC in L2 header or source IP in L3 header. By putting a flow rule around either of those fields and just counting the packets going through the switch that satisfy that rule, we can determine the number of packets being sent by the machine. This is useful information. To make it even more useful, one could add another flow to measure the packets going to our target machine. Adding a destination MAC or destination IP rule based on the machine’s MAC or IP address will accomplish that and using our two flows, we can now find out how many packets are coming and going out of the machine. The next question is, who is implementing the rules we just discussed above. There are several approaches and advantages/disadvantages of each approach, which I have discussed below:

  • Server Based Approach - Have S/W in the server itself to do the implementation of the rules. It’s the easiest way since the server already has to process the packets and it can keep track. The issue with this approach arises when it’s not a real server but a virtual machine on the server that we want to track. We can still let the hypervisor track the packets or ask the Virtual Machine to track it. The big disadvantage of this approach is that asking the server to do stuff on your behalf needs certain trust (security holes and digital certificates come to mind), depends on its capability and lowers performance. Since the server hypervisor has to measure these things, it needs to see the packets, making hardware based virtualization (SR-IOV) hard to adopt. Most of the data center bridging standards and IO virtualization standards are today going towards hardware based switch in the server and doing things in the S/W layers of the server is not going to be possible.
  • Server based with H/W offload - There is more talk around this than any real implementation but its worth mentioning that people have discussed putting special capabilities in the NICs on server to offload some flow processing. The advantage is performance and security (since the Hypervisor controls the NIC, the Virtual Machine can’t circumvent it). The disadvantage is cost and scaling issues. The chips capable of doing this (TCAMs etc) are expensive and trying to orchestrate across large numbers of servers severely limits the scale. We are already seeing Intel Sandy Bridge architecture coming to life which is integrating 10GigE NICs. Adding TCAMs will only increase the basic cost by $800-900 and also add significant complexity.
  • Probe Based Approach - Have probes in the network to do it. There are companies  which specialize in inserting probes in the network and collecting data that can do this quite well, as long as you only want to observe things. If redirection or traffic shaping action is needed, these passive probes will not work and inserting them requires intrusive work in cabling etc. Not my favorite approach either.
  • Switch based approach - Since all the traffic passes through the switches anyway, having them do it makes a lot more sense. The modern switch chips have H/W based CAMs and TCAMs which can take a rule and do the needful without adding to the latency or throughput of the packet stream. In my past life, as Architect of Solaris Networking and Network Virtualization, I have done the software based approach, but given the growing Virtual machine density, SR-IOV type features and growing need for analytics and traffic shaping with performance, I think that the switch based approach is far superior. Here, the CAM and TCAM that measure flows are the Hardware pieces. The software piece is able to add and delete rules on the fly. And Openflow provides a pseudo standard that allows a programmer to work and program any switch. But the biggest advantages are scale, ease of use, and administrative separation of this approach. The scale comes from orchestrating your flows and policies across fewer devices (one switch for approx 50 servers). Also, the people in charge of networks and storage networks are at times different and keeping the administrative separation is useful although not required.
So needless to say, we have currently taken the approach of solving this problem on the switch in conjunction with coordinating with the host, using standards like EVB/DCB etc which we will discuss at a later time. Given that new generation switch chips are very similar to the server CPU and also have the same complexity, the problem calls for a real Operating System on top, which can then help us write openflow based applications. This is where we step in. Part of Pluribus Networks’ effort is around implementing a distributed network hypervisor (called Netvisor™, a key component of the nvOS™ operating system) to give openflow programmers real teeth. We treat any switch chip the same as a server chip and most of the code is platform independent with very little that is written to the chip’s instruction set. Just the same way Linux code (with little platform specific stuff) runs on x86 or Power and OpenSolaris codes run on x86 and Sparc.

 

Current implementations

Now a little overview of projects and people who are leading the charge in the brave world of flows and Software Defined Networking. Before raking me over coal on the missing things, let me clarify that the stuff below is what I consider mainstream implementations that apply in world of data centers today (Disclaimer: I have purposely left out most of the research efforts that didn’t reach a mainstream product since there are too many):

  • The discussion has to start with project Crossbow which I believe is the first flow implementation with dedicated H/W resources approach that was available in OpenSolaris in 2007 and finally shipped in Solaris 11 (delayed courtesy the Oracle/Sun merger). The virtual switching in Host and H/W based patents (7613132, 7643482, 7613198, 7499463, etc) were filed by me and fellow conspirators from 2004 onwards and awarded from 2009 onwards. Keep in mind that when Crossbow had virtual switching with a H/W classifier running in OpenSolaris, Xen etc were just coming out with S/W based bridging. The 2 commands - flowadm and dladm allow users to create Flows and S/W or H/W based virtual NICs that can be assigned to virtual machines. This is the Server Based Approach that ships in main stream OS and is pretty widely deployed.
  • A similar approach has been adopted by our fellow company Nicira in the form of their NVP Architecture. They enhanced the offering by allowing an Openflow based Orchestrator to control the virtual switching in the host although their focus has primarily been on the virtualization side and not so much on application flows side.
  • Another of our sister and partner companies, Big Switch Networks has taken a hybrid approach of orchestrating any Openflow capable device which can be a switch or a virtual switch inside a hypervisor. Since they are still in partial stealth, it would not be my place to talk about more details.
  • Obviously, every existing network vendor claims that they are working on SDN and openflow. But by definition, SDN requires programmability and Operating Systems to run your programs on. Most of the existing network vendors lack the know how or the ability to do this. They have rich bank balances and if they can acquire the right companies and leave them alone, then they can potentially bridge the chasm (although it is going to be painful).
And then its the effort of yours truly at Pluribus Networks. It’s a well kept secret that we are building Server-Switches that run our distributed Netvisor™ which has massive flow capabilities and would be ideal for all the people developing stuff in the SDN space. But then we are in stealth mode and there is much more to us which we will get around to discussing in coming days :-) .