Nowadays, common systems in the area of high performance computing exhibit highly hierarchical architectures. As a result, achieving satisfactory application performance demands an adaptation of the respective parallel algorithm to such systems. This, in turn, requires knowledge about the actual hardware structure even at the application level. However, the prevalent Message Passing Interface (MPI) standard (at least in its current version 2.1) intentionally hides heterogeneity from the application programmer in order to assure portability. In this paper, we introduce the MPIXternal library which tries to circumvent this obvious semantic gap within the current MPI standard. For this purpose, the library offers the programmer additional features that should help to adapt applications to today's hierarchical systems in a convenient and portable way.