[HECnet] Thousands of DECnet errors on Tops-20

[Johnny Billquist]

On 2021-01-17 23:10, Thomas DeBellis wrote:
> 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).

Well, as noted, DDCMP exists both over synchronous and asynchronous 
serial lines. And DDCMP did run over some other stuff as well.

> 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).

Ok. Yeah my thinking was the equivalent of SLIP. It exists primarily in 
VMS, where you can (if I remember right) even turn on DDCMP on a line 
where you just logged in, which would be the thing on a dial up line. 
RSX is a little more static in that serial lines using DDCMP have to be 
configured in advance, and then cannot be used for normal terminal action.

> 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.

Definitely interested in what size we are talking about here, but I am 
sortof suspecting you are getting 1500 byte frames, and it sounded like 
the code you looked at suggested the maximum frame size to be slightly 
short of this.

As for DDP, it's totally unrelated to this, so how about playing with 
that another day?

Also not sure why you think it would be shared from a hardware perspective.

> 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.

Would be a bit interesting, yes.

> 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.

Ouch. :-(

   Johnny

>> ------------------------------------------------------------------------
>> 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 

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol