Multipath forwarding consists in using multiple paths simultaneously to transport data. While most techniques in this area require endpoint modifications, this article proposes to do it inside the network, transparently to the hosts. This approach, however, is known to introduce packet reordering at the receiving end, which may cause critical performance degradation. We present a Software Defined Network architecture which automatically sets up multipath forwarding including solutions to those issues, both at the sending side, through multipath scheduling algorithms, and the receiver side, by resequencing out-of-order packets in a dedicated in-network buffer. A prototype of the model is implemented with wide-spread technologies and evaluated in both emulated and real networks. The results show consistent throughput improvements, thanks to the use of aggregated path capacity. Comparisons to Multipath TCP are given, where we show our approach can achieve similar performances, while offering the advantage of endpoint-transparency.