Software Defined Networks (SDN) and OpenFlow have been proposed as the basis of the next generation of networks . In this article, I would like to focus on one specific type of network – the next-generation, cloud-inspired data center network – and cover: (a) some of the key requirements for those data center networks; (b) how SDN/OpenFlow address those requirements; and (c) why it is so important for Open Standards to be part of SDN.
Data Center Requirements
We frequently hear the following requirements from the next generation of data networks:
Efficiency – how can the network help me achieve higher server utilization, one of the driving functions in data center economics? Amazon must have figured this out in order to run EC2 – can I do that too?
Agility – how can I make my network respond to the servers and VMs/applications in the timescales they need (minutes/hours instead of days/weeks)?
Scalability – because of server virtualization and server HW advances, I can now put hundreds of VMs on a single server? I then need my applications running on everything from a single server to all the way across multiple of my data centers. Can my network handle that?
Simplicity – all of the above has to be done easily and simply. My staff and I are being called upon to handle more every year, and my current methods of operating, migrating and upgrading the network aren't scaling.
SDN and OpenFlow in the data center
The next-generation data center has posed a great challenge to traditional networking technologies. How does an SDN based on OpenFlow satisfy each of these requirements?
Efficiency. Much of the inefficiency in today's data centers comes from the need to segment the network into pods corresponding either to VLANs or IP subnets. Unfortunately, workloads don't come in such neat packages, and often enterprises find that an application has outgrown its current pod and then face an uncomfortable, labor-intensive migration.
An SDN with OpenFlow-based forwarding and the network virtualization allow users to simply segment the network exactly to the needs of the workloads. It allows the creation of “tailored-to-fit” networks rather than networks that come only in sizes that are powers of 2.
Agility. Server virtualization has succeeded in part because it is so easy for server administrators to create a single new VM nearly instantly. The speed of adding to the network or changing the network (a la VMotion) has highlighted the disparity in network agility and speed. Typically, changes to the network require trouble tickets as configuration changes are pushed down via CLI scripting and then checkpointed and backed up.
An SDN with dynamic, OpenFlow-based forwarding and its centralized model and programmability allows the network to change its forwarding behavior almost instantaneously in response to server changes.
Scalability. Hundreds of VMs on a single server means that where a network admin once saw a thousand server addresses, that same admin now see hundreds of thousands of VM addresses. It's difficult for network admins to keep up with that explosion of addresses, but an SDN based on OpenFlow can help centrally control this address explosion by providing allowing the network admins to describe the intended policies across across all the switches in the network, including the hypverisor switches.
Further, the network needs to be able to grow flexibly beyond a rack, a pod, or even a data center. Again, an SDN can directly program the network components, even across data centers, to allow the same policies to be enforced throughout the network.
Simplicity . One of the key advantages of SDN and OpenFlow is its simplicity – it allows all the first three requirements to be done from a central point of control, meaning the network admin is specifying network-wide connectivity, security, and performance policies. This reduces the admin's cognitive load from managing the separate configurations of hundreds or thousands of networking devices to managing a single, centralized configuration..
OpenFlow and the importance of Open Standards
Looking over each of these challenges and how SDN and OpenFlow solves them, it is important to remember how we've gotten here – the next generation network is being built with open standards unlike any others that have come before.
While we've, of course, had standard protocols in networking to date (OSPF , STP, and BGP , for example ), those protocols have not allowed the level of control, access and programmability offered by OpenFlow in an SDN architecture. This allows companies to develop and provide innovative solutions to network problems (such as those posed by new data center networks ) in just a fraction of the time it has historically taken.
Further, the openness of SDN standards, such as OpenFlow, means that an entire ecosystem of vendors can participate in the solution. This yields a broader and more diverse set of solutions, rather than a single solution from a closed vendor. Again, those will come to market more quickly than ever before.
Omar Baldonado , Head of Product Management at Big Switch Networks, has spent most of his 20-year networking career on centralized network analysis and control solutions. He holds over a dozen networking-related patents and has a BS and MS in Computer Science from Stanford University.