We present here methods that optimaly design a network built on two layers with discrete costs. This case occurs when we globaly design a virtual network (IP) on a sparse physical network (WDM). The models used results from the projection of the flow variable formulation on the binary capacity installation variables. This document is especially focused in algorithms solving a sub-problem of 2-layered network design. Its formulation expressed with binary variables is close to the famous multiple choice multidimensionnal knapsack problem (MCMK). We give numerical results for two-layered network instances obtained with a global method using algoritms inspired from the MCMK form of the master problem and compare optimal and approximate solutions for different cost configurations.