  The geometrical shapes and the physical properties of stellar wind --
interstellar medium interaction regions form an important stage for studying
stellar winds and their embedded magnetic fields as well as cosmic ray
modulation. Our goal is to provide a proper representation and classification
of counter-flow configurations and counter-flow interfaces in the frame of
fluid theory. In addition we calculate flows and large-scale electromagnetic
fields based on which the large-scale dynamics and its role as possible
background for particle acceleration, e.g. in the form of anomalous cosmic
rays, can be studied. We find that for the definition of the boundaries, which
are determining the astropause shape, the number and location of magnetic null
points and stagnation points is essential. Multiple separatrices can exist,
forming a highly complex environment for the interstellar and stellar plasma.
Furthermore, the formation of extended tail structures occur naturally, and
their stretched field and streamlines provide surroundings and mechanisms for
the acceleration of particles by field-aligned electric fields.
