An Overlay Network is a Network that changes the existing behavior of the Base Network to achieve some goals like more efficient use of the Links etc. What this means, is that even without the Overlay Network, the Base Network has the perfect capability to carry a packet from the Source to the Destination.

An overlay network can consist of a few or a large number of vEdge routers. A single vManage NMS, which provides management and configuration services to the vEdge routers, can support up to about 2,000 routers, and a vManage cluster can support up to about 6,000 routers. vEdge Join Overlay Network with one of these Methods:

In addition, since it is a routed network, the benefits of ECMP are leveraged, resulting in different paths being utilized for traffic between the same pair of VTEPs. Now, the follow-up question is, what is carried in the overlay and why is the overlay required in the first place?

BGP EVPN is a standards-based distributed control plane for Network Virtualization Overlay (NVO) that provides Layer 2 and Layer 3 connectivity over IP or IP/MPLS underlay networks. Initially designed for use with MPLS data plane in service provider networks, EVPN has been widely adopted in data centers as a control plane mechanism for VXLAN ...

A network fabric, or simply a fabric, is a collection of interconnected network nodes forming a scalable, resilient and high performance network architecture. A fabric can also be defined simply as an overlay or a logical topology used to virtually interconnect devices and built on top of a physical underlay topology that is being abstracted by ...

Basically Underlay is the actual network, ie all the hardware and Wan links so nitty gritty of setting up a network connection. Overlay is abstraction of that network which makes it simpler for engineers to connect from the Campus to cloud.

Centralized control policy affects the network wide routing of traffic by manipulating the routing information exchanged by the Overlay Management Protocol (OMP). OMP is a uniform control plane protocol designed specifically for overlay network and responsible for the overlay routing, data policies distribution and other functions.

The basic idea here is to make the communication between VM's using the overlay network created by the VXLAN. The requests from VM#1 to VM#2 will be destined for VM#2's MAC address. The request will also be sent to the VTEP, which is located on the host and will be checking VNI looking for the VM, which the source is associated with.

Nowadays, we already have SDN but with VMWARE NSX, running VXLAN Overlay Networks, and I can say that everything told on this webinar is 100% percent true. One of the networks that we have virtualized is a BGP + ASN, OSPF with HA VPN Site to Site IPSec, network between 2 Data Center, running and connected witch overlay VXLAN NSX over our IP BGP ...

Now, the next task is to build an overlay control plane with VXLAN BGP EVPN on-top of the BGP underlay transport network. The overlay control-plane is an address-family in BGP referred to as "L2VPN EVPN"; the L2VPN address-family will be configured under the same BGP instance that was configured for the BGP underlay.