A system, controller and method having centrally optimized coding for a source routed forwarding based multicast network. The network comprises a plurality of nodes configured to transfer data packets to one another via a plurality of links. A controller is configured to control each of the nodes, and is configured to control forwarding of the data packets by establishing a header for each flow. The header defines a path for the flow of the data packets from a source to multiple destinations, wherein the length of the header is a function of the nodes and the branches in the path. The multicast path is represented as a header that consists of codewords representing interfaces, links and instructions. Some of the codewords are assigned different lengths in order to reduce the size of the header. Other codewords have a fixed size comprising a bit field.