A multipath routing architecture for large data transfers is disclosed. The architecture employs an overlay network that provides diverse paths for packets from communicating end hosts to utilize as much capacity as available across multiple paths while ensuring network-wide fair allocation of resources across competing data transfers. A set of transit nodes are interposed between the end-hosts and for each end-to-end connection, a transit node can logically operate as an entry gateway, a relay or exit gateway. Packets from the sender enter the entry node and go to the exit node either directly or through one of a plurality of relay nodes. The exit node delivers the packets to the receiver. A multipath congestion control protocol is executed on the entry node to harness network capacity for large data transfers.