Creation of a virtual overlay for a multipath network with tiered topology is disclosed. A virtual-node module may group network nodes connected within a common tier, which is initially the tier furthest from the core. This module may also group network nodes at a consecutive tier, closer to the core, that connect a pairs of groupings in the common tier by links between the common and consecutive tiers. Groupings with a common network node may be combined and designated as virtual nodes. A virtual-link module may sum bandwidths for network links between virtual-node pairs with nodes in both the common and consecutive tiers. A check module may combine virtual nodes and links and network nodes and links not yet virtualized in a graph, which it may check for a cycle. An iteration module may iterate both tiers toward the core, triggering further grouping, summing, and updating until no loop exists.