Institutional grids consist of the aggregation of clusters belonging to different administrative domains to build a single parallel machine. To run an MPI application over an institutional grid, one has to address many challenges. One of the first problems to solve is the connectivity of the different nodes not belonging to the same administrative domain. Techniques based on communication relays, dynamic port opening, among others, have been proposed. In this work, we propose a set of Grid or Web Services to abstract this connectivity service, and we evaluate the performances of this new level of communication for establishing the connectivity of an MPI application over an experimental grid.