Re: DECnet, LAT, Cterm over IP/GRE - Timeout?
From: John E. Malmberg (wb8tyw_at_qsl.network)
Date: 03/20/05
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Date: Sun, 20 Mar 2005 00:38:04 -0500
Scott Fisher wrote:
> All,
>
> (Warning, this may be a bit long, but we did lots of testing and I
> wanted to present some facts).
>
> Question:
> Could we be timing out a DECserver (DS100, DS200) or Cterm across WAN
> (T1) and if so, what timers might I check? Or, do you have a better
> idea on my problem?
>
> Situation:
> We have a WAN (T1) with Alphas, DECservers (DS100, DS200), and windows
> boxes. Everything is fine. We run IP, DECnet, MOP, etc across the wan
> without problems. The DS100 downloads across the wan without problem.
> We want to move to MPLS which requires that all packets are IP – thus
> the problem with the DS100 and DECnet. We have an older application
> that requires VTs and attached printers and it will not be going away
> for a few years. Also, we rely on VMS Copy, Cterm, and submit/remote on
> the remote alphas. I know we can do things with ftp, telnet, dcl, etc,
> but it would be nice not to have to mess with that.
>
> Testbed:
> We can, in principle, do the IP thing (yes, with LAT too), by using GRE
> on our routers. We have created the following testbed:
>
> Alpha-A, DS100, DS200, Router -cable- Router, Alpha-B
>
> Running the routers back to back in our lab. It is running and
> basically functions (see below).
>
> Facts:
> 1. We can boot the DS100 and it will download from Alpha-B (i.e.,
> across the network). Works 100% of the time.
Brief use of MOP protocol.
> 2. From VT on DS100, we can connect to Alpha-A just fine. We can
> leave it logged in all day just sitting there and it will stay
> connected. No problems at all.
Exclusively LAT protocol.
> 3. We can connect from same VT to Alpha-B (across the MPLS with GRE)
> and it will connect just fine. PROBLEM: After about 20-30 minutes, it
> will “disconnect” from the service – the VT will talk to the DS100, but
> we are logged out of alpha-B. This problem happens at varying time
> intervals but 100% of the time.
Apparently the LAT protocol is having a problem from DS100 to Alpha B.
> 4. From VT on DS100, connect to Alpha-A, then $set host alpha-A (to
> itself). Works fine, stays connected.
> 5. From VT on DS100, connect to Alpha-A, the $set host alpha-B
> (across the network), connects fine, but times out after 5-30 minutes.
> Again, times vary but happens 100% of the time.
Apparently the DECNET protocol is having a problem from Alpha-A to Alpha B.
> 6. Copy large from Alpha-A to Alpha-B, it ran for 3 hours (big file
> for testing), and no problem at all. No timeout.
Was a CTERM(DECNET) connection like described in #5 set up at the same time?
> 7. From VT on DS100, connect to Alpha-A, then $telnet to Alpha-B. No
> problem, no timeout – ran for 1.5 days.
TCP/IP is more tolerant of some types of network disturbances than LAT
or DECNET.
> 8. Take all of this and do it in reverse to prove that it is on an
> alpha-a or alpha-b question. Results the same.
>
> So, it seems like we have some kind of a timeout going on, but I can’t
> think of where to go next. I apologize for the long message, but I
> think the data is important.
It may take a ethernet monitor to sort things out, with it specifically
monitoring the LAT or CTERM(Decnet) connections that you are having a
problem with.
It looks like there is definitely something different about Alpha B's
settings or connection to the network.
LAT is a non-routable protocol, and is sensitive to network disruptions.
DECNET is routable if the routers understand it. It can also be more
sensitive to network problems than TCP/IP. That might be adjustable,
but not an area that I have any current experience in.
-John
wb8tyw@qsl.network
Personal Opinion Only
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