Overlay networks
A virtual network which is built on top of a physical network is called an overlay network. Does that sound familiar by any chance? Most enterprise environments would have used VPN technology for securing private or public networks, which is an IP-over-IP overlay technology. However, it is very important to understand that not all overlay networks are built on top of IP networks. The real question is, why do we require an overlay network ? As we can see from the following figure, we have two data centers and each of these data centers is following a spine-leaf topology. Flexible workload placement and virtual machine mobility, along with strong multitenancy for each tenant, are common asks in a virtualized infrastructure:
VXLAN, MPLS, NVGRE, VPN, and OTV are some of the classic examples of network-based overlays. Let's go back to the roots of server virtualization. Server virtualization virtualizes a physical server and allows multiple virtual machines to run...
