Virtual network overlays for multipath datacenters

A system for generating a virtual overlay for a datacenter, comprising:

• a database, on a physical storage medium, maintaining a dataset capable of characterizing a tiered datacenter topology, operable for multipath routing, as a graph with a set of vertices representing network nodes and a set of edges representing network links;
• a controller, comprising memory and a processor, communicatively coupled to the database and operable to:
• access the graph from the dataset;
• create a set of virtual nodes by assigning network nodes, represented in the graph, to virtual nodes;
• create a set of virtual links between the virtual nodes by summing bandwidths of network links directly connected to network nodes in pairs of virtual nodes;
• generate a virtual overlay, with the set of virtual nodes and the set of virtual links, that assigns a single path between a source host and a destination host;
• and
• a virtual-node module communicatively coupled to the controller and operable, beginning at a tier most removed from a core tier of the datacenter, to:
• select a reference tier and a second tier, the second tier being defined relative to the reference tier and being one step higher on the tiered datacenter topology in a direction toward the core tier, the reference tier and the second tier being subject to reassignment after being used to generate the set of virtual nodes from network nodes;
• and
• generate the set of virtual nodes from network nodes, a virtual node of the set of virtual nodes comprising at least one network node in the second tier for which a path that includes the at least one network node in the second tier is describable through the datacenter from a corresponding, source node in the reference tier to a corresponding, destination node in the reference tier.