> I'd guess that running net pipe with 3 procs may be undefined.
It is indeed undefined. Running the net pipe program locally with 3 processors blocks, on my computer.
This issue is especially weird as there is no problem for running the example program on network with MPICH2 implementation, for 2 processes.
However, with MPICH2, it fails with 3 processes and blocks also on connect ("Connection refused"), which could indicate that it's actually a network issue, with both MPICH2 and OMPI. I don't know how many connections OMPI use to send the data in the example program, but with the assumption that it tries to open 2 connections (while for the same program, MPICH2 only uses one connection, which is another hypothesis), maybe the number of connections is the right way to look for. I'll ask MPICH2 users on their mailing list, so as to get their opinion about it.
Now that I know the program doesn't work both with OMPI and MPICH2 implementations, I guess it's not dependant of MPI implementation.
If you have any ideas or comments, I would be pleased to hear them.