Why was SDN born?What is the relationship with network virtualization?

2012年に引き続き、現在も旬なキーワードとして高い注目を集めているSDN（Software-Defined Networking）。SND/OpenFlowの基礎技術や最新動向をQ&A形式で解説していく本特集の第1弾では、そもそもSDNとはなんなのか？　SDNが生まれた背景などを解説していきたい。

What is SDN in the first place?

　"SDN (Software-Defined Networking)" refers to a network that can be flexibly defined by software and all technologies that realize it.With the rise of the typical technology "OpenFlow", it has been attracting attention since around 2011, solving existing network issues in settings and operation management, achieving network virtualization corresponding to cloud and virtualization.It is expected to be something to do.

　In SDN, the optimal network for applications can be configured from the software side without setting a cable wiring or network device, and multiple logical networks can be built on a single physical network.It is also a major feature that protocols and APIs for realizing these software control are opened.Currently, various vendors, including major vendors and ventures, are working on SDN.

Tell me the background that SDN appeared!

　Conventional networks were to connect physical devices such as servers, storage, and appliances, and the configuration was fixed according to the number of servers and application requirements.Therefore, when adding new services to existing networks, the optimal settings were required for various network devices, such as switches, routers, firewalls, and road balancers, and lacked flexibility.

　However, if the server virtualization progresses and it is operated by shared infrastructure, it will not be said.Virtual servers can be generated or disappeared according to policy, and even move to other host servers and data centers.The data center network, which consolidates the server, is a multi -tenant environment used by multiple customers with different requirements.It is extremely inefficient to change the network settings of virtual machines with conventional network virtualization technology, including VLANs and VPNs.

Changing network settings assuming a virtual server lacks flexibility (excerpt from the IPA site)

　SDN appeared to resolve these existing network management dissatisfaction.SDN can dynamically change the network configuration according to customer requirements and virtual machines.It also realizes highly flexible network virtualization that supports servers, storage and appliance virtualization.

Have you ever defined the network software?

　If you are a user who has been dealing with networks since then, many people have the question, "Isn't the definition of networks so used for software?"In addition, what can be used easily using a commercially available network management tool for issues that need to be set individually for network devices?You will think.

　Certainly, if it is a recent network management tool, you can easily set and manage multiple network devices.There are also high -performance tools corresponding to the change of topology in the event of a disability and the movement of virtual machines, and more and more products that can handle various network devices with multi -vendors are increasing.When this happens, it seems that there is no merit of SDN on the surface.

　Based on these assumptions, the merits of SDN will be integrated as "flexibility" and "programmable".The feature of SDN is that the operation of network equipment can be defined from the external program.Users can freely determine the necessary network configuration through the API.Like a server, the network can be treated as a dynamic resource.Furthermore, by linking with the operation management of virtual machines, a network operation that is not limited to labor saving but also automated.Doraming such a future is the biggest attraction of SDN that attracts various engineers.

(What is the virtualization of the network realized on the next page?)