SD-WAN node reachability

For the correct operation of ADVPN 2.0 mechanisms, the SD-WAN nodes must be able to communicate with each other across the overlay network. This is required for the Discovery process, but also for a subsequent triggering of additional shortcuts.

There are no constraints on a specific path that the ADVPN 2.0 control messages take on their way between the nodes, as long as they reach their destination through the overlay network. Typically, they will be routed through one or more Hubs on their way between Spokes. Neither the results of the Discovery process nor the selected shortcut path depend on the route taken by the control messages.

This is unlike the earlier version of ADVPN, where the route taken by the control messages determined the shortcut path selection. This decoupling, implemented in ADVPN 2.0, eliminates the need for a overlay stickiness policy (common in the earlier SD-WAN/ADVPN deployments) and allows greater flexibility, both in a single region and in multi-regional deployments.