[Info-vax] Loosing all LAT connections on one machine in DECNet Network

[JCamCMKRNL]

I have a Dedicated network (10-Base5 ethernet) which only runs DECNet
traffic on it. This network has 5 Machines on it (four PDP-11/RSX11M+
and one VAX/VMS) and several DECServer 200MC terminal servers.

Recently on a few occasions (three times in the last three weeks) all
the LAT connections to the one VMS Machine are dropped. The users who
were logged in are disconnected, and their interactive process
terminates, returning them to the DECServer "Local>" prompt. When they
enter in the DECServer command "SHOW SERVICE" we see all the other
machines, but not the VMS Machine.

The VMS machine is still running fine, and there are no additional
device errors. We can still log into any one of the PDP-11 systems
through LAT on the DEC Servers, and then connect to the VMS system via
the SET HOST command, but still cannot connect to the VMS system via
LAT.

There were no Network messages logged to OPCOM, and the LATACP process
is still running. Later, time passes (sometimes several minutes, and
other times several hours) and the service returns with no apparent
reason or operator interaction. On one of these occasions we performed
a system reboot of the VMS system, but this did not restore the LAT
service for the system immediately. Instead, the LAT service came back
about 15 minutes after the reboot.

I tried using the LATCP program to see if I could do anything when it
was in this state, and it seemed to be working fine, but I still could
not connect from any terminal server.

Our basic topology is: All the 5 systems and one DECServer are in data
center connected to a DELNI hub, which in-turn is connected to the
thickwire 10-Base5 backbone. This Backbone runs throughout the plant
to several IDF communications closets. Some of these closets have one
DECServer connected to the Backbone directly via a transceiver and AUI
cable, and others have Multiple DECServers connected to a DELNI which
in-turn is connected via an AUI Cable to the Backbone transceiver.

When we loose all the connections to the one VAX system the LAT
service disappears on all DECServers throughout the plant, including
the one in the data center which is connected to the one DELNI with
the 4 PDP-11s and one VAX system.

I have DECNet network logging turned "ON" on the VAX, and see no
network OPCOM messages. I see no feature in LATCP to enable logging.

Based on this information I am reasonably sure that I am not dealing
with a hardware issue, because I can still connect to the PDP-11
systems via LAT and then connect to the VAX via SET HOST.

Is there a log file for the LATACP process?
Does anybody have any ideas as to how I might Diagnose this issue?

Any ideas would be deeply appreciated.
Jeff Cameron