The electrical grid is facing a significant shift from a centralized generation system to a more distributed setting where each portion of the grid is managed by a local control system and it can work both as a producer and as a consumer. This brings many advantages, but a cooperation mechanism between the different players needs to be established in order to ensure the overall network proper working conditions. This paper presents an optimization framework for the management of an aggregation of microgrids. The main objective is to show that, if properly coordinated, microgrids can give a significant support in terms of ancillary services provision. Finally, a distributed algorithm is described, designed in such a way each microgrid preserves its internal information and the control of its resources.