What’s cool about “Software Defined Networking”?

“Software Defined Networking” products are a new breed. One can find early examples of these switches on internet auction sites or searching for “open source switch”. The latest versions of software defined networking (or SDN) give users more control over how their network is put together and how it works. This allows users to make the network an integral part of a flexible infrastructure where resources are allocated and configured in response to services being provisioned at the endpoints.

As an example of what SDN can do for users, consider one of the best and worst parts of Ethernet. Spanning Tree. This protocol allows Ethernet networks to recognize when a loop or multiple paths exist between switches and disables redundant or parallel links to prevent packets from being repeated endlessly. While this was extremely handy 20 years ago, it now limits network engineers ability to build high performance networks because spanning tree (and LACP bonding) place limits on how many parallel paths there can be between switches. Contrast this with Infiniband, where truely massive fabrics with full bandwidth between all endpoints are trivial to construct and manage.

The difference is in the way the network is managed. Ethernet requires an algorithm that can be evaluated in a distributed environment with only local information because there is no central agent in an Ethernet network. But Infiniband has a central agent called a subnet manager that sees all the paths in the network and can distribute and allocate traffic to make use of all the parallel links between endpoints. It does this once at connection setup and then gets out of the way so there is no performance impact for this central intelligence.

In a similar way, SDN provides that central intelligence for an Ethernet network of switches and allows the network to make global decisions to optimize the network for the workload.

The icing on the cake is that it’s cheaper too.

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