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

[Chris Scheers]

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.
> 
> 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


If it turns out that it is not hardware, is it possible that there is a 
PC (or other 100MB equipment) connected to the backbone somewhere?

I had a similar problem with a DELNI/VAX/DECserver 200 environment once. 
  Periodically, LAT would go down, but DECnet would stay up.  (It did 
get noticably slower, though.)

The DELNI was connected to the company network, which was primarily 
100MB.  Periodically, something on the 100MB network would start 
generating enough data to swamp the 10MB DELNI, causing LAT to go down.

When the storm passed, LAT came back.

Putting a 10MB switch between the rest of the network and the DELNI 
solved the problem.

-- 
-----------------------------------------------------------------------
Chris Scheers, Applied Synergy, Inc.

Voice: 817-237-3360            Internet: chris at applied-synergy.com
   Fax: 817-237-3074