1. A method comprising: performing with a first cluster of first switching devices first multipathing through a network except through a second cluster of second switching devices within the first cluster; and performing with a second cluster of second switching devices second multipathing just through the second cluster, wherein switching devices of the first switching devices are compatible with a software-defined networking (SDN) protocol, wherein switching devices of the second switching devices are compatible with a protocol for an open systems interconnection (OSI) model layer, wherein the first switching devices comprise a plurality of border switching devices located at a boundary between the first cluster and the second cluster, each border switching device also compatible with the protocol for the OSI model layer, wherein each second switching device is directly connected to just a pair of the border switching devices, and just routes network traffic between the pair of the border switching devices through the second cluster of the network, such that the first switching devices and the second switching devices together effect end-to-end multipathing through both the first cluster and the second cluster of the network.