Chapter 8. Overlay Networking

What is it and what problems can we solve with it?

These are the first questions that any good network engineer will ask when he first encounters a new technology or feature.

One of the larger problems in the data center is being able to easily orchestrate compute, storage, and networking to provide data center services with a click of a mouse. There are tools such as OpenStack, CloudStack, VMware vSphere and others that can help you accomplish this goal. The problem with these tools is that special plugins are required to help orchestrate the network. For example, if a new virtual machine (VM) was created and required to be on a separate network, the orchestration software would have to use a plugin to automatically configure the network switches with new Virtual Local Area Networks (VLANs), default gateways, and Access Control Lists (ACLs). The problem is that plugins only offer basic functionality and the feature parity varies between vendors. The other problem is that every time you create a new VM, add a NIC to an existing VM, or move a VM, it requires a change to the physical network.

One method of solving these problems is to decouple the virtual network from the physical network. The basic premise being that if all changes were made on the virtual networks, the physical network wouldn’t require changes. The tradeoff is that you’re moving complexity from one location to another. In this example, we’re moving physical network changes to ...

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