[HECnet] Network topology according to MIM.

It's fine to use just a basic network topology. My point was that the topology you objected to is a valid and desirable real world topology (in other settings, arguably). But note that unless your topology is exactly a tree (no redundant paths at ANY spot), you may have asymmetric paths. Consider two paths A-B-Q-X and A-C-P-X (with equal circuit costs throughout). A-X traffic would go A-C-P-X, X-A traffic would go X-Q-B-A. That's normal. Asymmetry is not a problem; the DECnet architecture has absolutely no interest in avoiding such a thing. What it does try to do (and in this it explicitly differs from IP routing algorithms) is "determinism": any given network topology will, in the steady state, behave in a consistent way independent of what sequence of events lead to that topology. This is, for example, why DECnet has tiebreaker rules in route selection and designated router election that are designed for determinism, unlike, say, the OSPF designated router election that explicitly aims at a different property. (One can argue forever which choice is better, and I don't intend to get into that now; the point simply is that DECnet chose that principle and applied it consistently, while other designers chose differently.) paul