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The figure depicts two pairs of geographically-redundant sites, four sites in total.
The first geo-redundant pair, consisting of Site 1 and Site 2, are peers shown performing data synchronization and health monitoring with each other across a WAN IP backbone.
A second geo-redundant pair, consisting of Site 3 and Site 4, is depicted identically to the first pair, communicating over the same WAN IP backbone.