This chapter discusses one of the most important incarnations of Software-Defined Networking (SDN) for clouds and data centers: Network Virtualization Overlay (NVO).
Chapter 10 introduced the Edge Forwarder concept in detail. Now, let’s have another look at it from a functional and service-centric perspective. In the context of NVO, Edge Forwarders support multitenancy by implementing flexible network policies that rely on an overlay transport mechanism. You should know that this is basically the definition of a VPN; thus in this chapter, Edge Forwarders are actually VPN Forwarders.
One type of VPN Forwarder, network devices that implement L3 VPNs and L2 VPNs, has already been the subject of many pages in the first part of this book. These PE routers can run in dedicated physical platforms, or virtualized in a container, or as a VM in a hypervisor, or even directly on a bare-metal server. Anyway, physical or virtual, they perform the same function—of course, performance differs.
This chapter focuses on two other VPN Forwarder types:
Host operating system (OS) that implements virtual networks (VNs) while acting at the same time as a Hypervisor or as a Container Engine. As you are about to see, this is not the same as a network OS running on a virtual machine (VM). From the computing perspective, it is lower in the stack and hence more native. But these approaches are not mutually exclusive; actually, they combine nicely in Network Functions ...