Hello Manoj
One of the fundamental design characteristics of Cisco’s SD-WAN solution is the fact that it uses an overlay network. This overlay network is created using VPN0 which is the tunnel interface configured in all the devices. It is also the overlay network via which all SD-WAN functionalities and mechanisms take place.
Why do we need it for the vManage, vBond, and vSmart devices to operate? Well, it’s just a matter of design. Could Cisco have designed it so that communication between these devices doesn’t go through the overlay network? Probably yes. However, I believe that they chose to deploy it like this for a couple of reasons:
- All of the vEdge devices need to communicate over the VPN0 overlay network, and will forward all of their user traffic over that same overlay network. Since communication must take place between the vEdge devices and the various controllers, it only makes sense to allow the controllers to use the same communication paths.
- In the lesson, the vManage, vBond, and vSmart are all in the same physical location. What if you want to deploy several of these in other physical locations? By using VPN0 it simplifies such communication in a scenario like that.
These are simply my thoughts about why they did it, and there may be additional reasons, but fundamentally, it is a design choice.
I hope this has been helpful!
Laz