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

[John E. Malmberg]

JCamCMKRNL wrote:
> 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.

Based on past posts on comp.os.vms and entries like this Ask The Wizard 
one below, I would put some suspicion on the DELNI that is common to the 
interruption.

http://h71000.www7.hp.com/wizard/wiz_1585.html

When I worked more directly with networking hardware, I would use a 
network sniffer to look at the packets to see what was going on.

Wireshark is a free network sniffer that you can install on Linux or 
even Windows.

-John
wb8ytw at qsl.network
Personal Opinion Only