SD-WAN - vEdge full mesh

By default, in an SD-WAN implementation, the vEdge devices are set up to communicate in a full-mesh manner. This means that all sites can communicate with each other directly.

However, this assumes that the underlay network that is serving the SD-WAN topology must also have established direct communication between all parts of the network to achieve this. What happens if the underlay network itself doesn't have this direct communication? Such as in the case of a DMVPN Phase 1 scenario?

So if you have topology where two vEdge devices cannot communicate directly over the underlay due to the restrictions of that underlay network, but each can each communicate with the main site where the controllers are hosted, the Cisco SD-WAN fabric will inherently handle the situation to a certain extent. The system’s OMP and TLOC properties will play a role in determining viable paths.

If direct communication between two vEdges is not possible due to underlay restrictions, the initial tunnel establishment will fail. However, even if a direct path isn’t available, when they need to exchange data, the traffic will inherently use the main site as a relay point since a direct path isn’t viable. This is part of the SD-WAN’s inherent path decision mechanism.

So based on the OMP path attributes, the vEdge will choose the best available path. If the direct path is unavailable, it will select another path, like through the main site.

This is not to be confused with the SD-WAN Hub and Spoke topology option which takes a full-mesh topology and restricts communication such that each vEdge can only communicate with the main site.