Yes, indeed. It wasn't even meant to work. Here's an excerpt from the
DECnet (Phase IV) manual:
DECnet supports a variety of types of nodes developed during different
phases
of DNA implementation. Phase II, III, and IV nodes and DECnet/OSI nodes
can all exist on a network. There are con guration restrictions in such
a mixed
network; one major restriction is that only nodes running adjacent
phases can
communicate directly, ...
Exactly. The other restriction is that both endpoints of an application connection have
to understand the same protocol. Since there haven't been a whole lot of application
layer changes between Phase III and IV, that shouldn't be a big issue. The most
obvious one is "set host" which switched from the OS-specific versions to Cterm
(in some operating systems). But the old ones are often still supported. Things like
file transfer are likely to be fine.
Phase II is a different story, but implementations that old are probably very hard to
find.
Later there is mentioned that a Phase III node can exist in an Phase IV
area as an end node. It can communicate with a Phase V node through
the Phase IV area.
paul