The aim of this paper is to optimize tra±c distribution coefficients in order to maximize the trasmission speed of packets over a network. We consider a macroscopic fluidodynamic model dealing with packets flow proposed in [10], where the dynamics at nodes (routers) is decided by a routing algorithm depending on traffic distribution (and priority) coefficients. We solve the general problem for a node with m incoming and n outgoing lines and explicit the optimal parameters for the simple case of two incoming and two outgoing lines.