Multi-layer optical networks have recently evolved towards IP-over-WDM networks. Therein, in order to avoid protection/ restoration redundancies against either single or multiple failures, synergies need to be developed between IP and optical layers in order to reduce the costs and the energy consumption of the future IP-over-WDM networks. The authors propose two new optimization models. The first one is an enhanced cut-set model, relying on a column generation reformulation. The second one is a path model, based on a multi-flow formulation. Both models can solve exactly most benchmark instances, which were only solved heuristically so far.