SDN is a great new way to think about the networking. But, till today, it was difficult for a software-defined network to communicate with the external world.

SDN重新定义了网络架构，但是直到今天，SDN网络仍很难与外部网络进行通信。

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For Google, software defined networking represented a better way of moving traffic between its global data centers.

FORBES: Google Unveils Secret, Worldwide Networking Project

Google is not alone in its embrace of software defined networking but it is the first company to have implemented it on such an enormous scale.

FORBES: Google Unveils Secret, Worldwide Networking Project

The protocol, which was initially conceived by a graduate student at Stanford University named Martin Casado, represents a new way to control network switches and routers that has come to be known as software defined networking, or SDN.

FORBES: Google Unveils Secret, Worldwide Networking Project