I am trying to get the value of MPI_TAG_UB using the following code: MPI_Aint * maxTag;; int error, flag; error = MPI_Comm_get_attr(MPI_COMM_WORLD, MPI_TAG_UB, &maxTag, &flag); if(error != MPI_SUCCESS || !flag ){ printf( " ERROR IN native mpitagub\n"); } printf( "mpitagub = %d\n", *maxTag); For MPICH3 I get mpitagub = 1073741823 I also did it for OpenMPI and I get mpitagub = 2147483647 The value from OpenMPI makes sense since its 2^31 -1. But at the end the MPI_TAG_UB is MPI implementation dependent. *So I was wondering the value that I got from MPICH3 (mpitagub = 1073741823) is this OK? or my code is wrong somewhere?* Thanks Bibrak