[HECnet] Thousands of DECnet errors on Tops-20

[Thomas DeBellis]

The only serial lines that I saw DECnet running on were synchronous 
connections.  The local connections between CU's 20's (before we got the 
CI's and NI's) were 56K baud synchronous lines running on KMC11's, which 
we thought were pretty hot stuff ...until...  Non-data center 
connections (our chemistry VAX, CMU & CWR 20's) were asynchronous lines 
running 9.6K baud (on DUP11's, I think).

The PANDA monitor's Multinet code implements serial IP (SLIP), which it 
will run over an ordinary DL or DH based asynchronous lines.  I didn't 
immediately see anything similar for DECnet, but it is doubtful that MRC 
would have put that it in; the code was supposed to run on a 2020, which 
has different IO drivers.  If his 2020 5.0 changes ever do surface, it 
may be conceivable that some of them might be retrofitted into 7.1 
(depends on what's applicable).

It is now possible that I will eventually figure out what this 
mysterious DDP device is.  I reconfigured both 20's to have the largest 
buffer possible (DECNET BUFFER-SIZE 1476 in SYSTEM:7-1-CONFIG.CMD, which 
I checked in the running monitor), rebooted /and/ ... I'm still getting 
the same frame too long error, viz:

    ***********************************************
    DECNET ENTRY
      LOGGED ON 16-Jan-2021 01:29:38-EST      MONITOR UPTIME WAS 0
    day(s) 0:16:8
             DETECTED ON SYSTEM # 3691.
             RECORD SEQUENCE NUMBER: 35752.
    ***********************************************
    DECNET Event type 5.15, Receive failed
     From node 2.522 (VENTI2), occurred 16-JAN-2021 01:29:11

       Line NI-0-0

       Failure reason = Frame too long
       Ethernet header = AB 00 00 03 00 00 / AA 00 04 00 08 0A

    ***********************************************
    DECNET ENTRY
      LOGGED ON 16-Jan-2021 01:29:38-EST      MONITOR UPTIME WAS 0
    day(s) 0:16:8
             DETECTED ON SYSTEM # 3691.
             RECORD SEQUENCE NUMBER: 35753.
    ***********************************************
    DECNET Event type 5.15, Receive failed
     From node 2.522 (VENTI2), occurred 16-JAN-2021 01:29:28

       Line NI-0-0

       Failure reason = Frame too long
       Ethernet header = AB 00 00 03 00 00 / AA 00 04 00 FF 0B

    ************************************************************************

Darn it‼️  So now I've got some modifications to actually make to the 
monitor to give some better error information (like the number of bytes 
overrun, if I can extract it).  So maybe I'll stumble over whatever DDP 
does.  It's odd; I can't think of any device that a pack of KL's could 
share except something like a dual ported disk or magnetic tape drive 
and that's only two KL's.

Meanwhile, I'll also do a tcpdump so I can try to correlate what Tops-20 
is silently whining about with what's coming over the bridge.

Finally, something to beware of if you are running the KLH10 
micro-engine and have a very large file that you're backing up (you're 
all running regular backups, /right/?)  The amount of disk activity will 
somehow prevent KLH10's front end timer from popping so, unless you are 
running my changes to DTESRV, you're going to /hang/ with a DTEKPA 
BUGINF.  A quick hack is to deposit a -1 into FEDBSW, which will keep 
the 20 from trying to reboot the front end (which KLH10 absolutely does 
not know how to handle).

So the quarterly full backups worked fine on the development machine 
(VENTI2) which has the patch, but not on the production machine (TOMMYT) 
which does not.  Pity, I had been up over 32 weeks and was only a little 
short of 3,000 hours uptime.
> ------------------------------------------------------------------------
> On 1/15/21 11:58 PM, Johnny Billquist wrote:
>
> I saw that and wondered as well.
> I was thinking maybe it could be for DDCMP devices without more 
> specifically defining what it would be, since DDCMP could be run over 
> any serial line?
>
>   Johnny
>> ------------------------------------------------------------------------
>> On 2021-01-15 22:53, Peter Lothberg wrote:
>>
>> The 2020 has a KMC11 and up to 2 DUP11, and those are the interfaces
>> the "MRC T20 DECnet thing supports.
>>
>> On the list of devices/sizes you posted is  a "DDP" device and I 
>> wounder if you knew what that is?
>>
>> --P
>>> ------------------------------------------------------------------------
>>> *From*: "tommytimesharing" <tommytimesharing at gmail.com>
>>> *To*: "hecnet" <hecnet at Update.UU.SE>
>>> *Sent*: *Friday, January 15, 2021 4:24:07 PM
>>> *Subject*: *Re: [HECnet] Thousands of DECnet errors on Tops-20
>>>
>>>     DDP?  I thought it was DUP-11.
>>>> ------------------------------------------------------------------------
>>>>
>>>> On 1/15/21 4:21 PM, Peter Lothberg wrote:
>>>>
>>>> Well, MRC was receiving "suggestions" from Stu Grossman on how to 
>>>> do it, but if my memory does not fail me the block size was 312, 
>>>> due to lack of buffer space in the already crammed single section 
>>>> 512KW 2020.  I'm afraid my tape and disk-pack are in Seattle.  I 
>>>> knew it was not 576 as it had two DUP-11's and using it for transit 
>>>> failed...
>>>>
>>>> Quiz, do you knew what a DDP is?
>>>>
>>>> -P 
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