1. A system comprising: a virtual data center manager in a physical data center for allocating bandwidth and allocating a plurality of routing paths for a plurality of virtual data centers, the physical data center comprising a plurality of servers and a plurality of switches; the plurality of servers configured to perform packet classification and to define a particular path of the plurality of routing paths with source routing; and the plurality of servers and the plurality of switches configured to implement priority queuing for the plurality of routing paths.