Ethernet VPN (EVPN) is a technology for connecting Layer 2 (L2) network segments separated by a Layer 3 (L3) network. It accomplishes this by constructing a virtual L2 network over the underlying L3 network. This setting up of virtual network overlays is a specific kind of network virtualization.
So, we begin our journey to the world of EVPN by studying network virtualization. This chapter covers types of network virtualization, including in more detail the specific type of virtualization called Network Virtualization Overlays (NVOs). Staying true to a practitioner’s handbook, this chapter largely focuses on understanding the ramifications of NVOs for a network administrator. We study network tunnels and their effects on administering networks. A little history provides context for the broader technology called network virtualization and adds color to the specifics of Virtual Extensible LAN (VXLAN), the primary NVO protocol used with EVPN within the data center. We conclude with a brief survey of alternate control-plane choices and the availability of network virtualization solutions. By the end of this chapter, you will be able to tease apart the meaning of the phrase “virtual L2 network overlay.”
This section begins by examining the raison d’être for virtual networks. We then examine the different kinds of virtual networks, before concluding with the benefits and the challenges of overlay virtual networks.