[Simh] Cluster communications errors

[Mark Pizzolato]

On Friday, July 20, 2018 at 6:05 AM, Hunter Goatley wrote:
> On 7/20/2018 7:58 AM, Paul Koning wrote:
> > Is that the Ethernet interface down/up that happens when DECnet sets the
> > MAC address?  I assume you don't have a card that supports multiple MAC
> > addresses.
> 
> It probably is. That makes total sense, and I should have realized that.

I'm quite sure that the MAC address change happens much earlier than 
the DECnet startup when a VMS cluster is configured on the system.  As 
soon as the booting system gets its SYSGEN parameters and knows its 
SCSSYSTEMID it 1) has enough info to set the DECnet MAC address and
2) is capable of engaging in cluster communications using this ID (and MAC).

> > On the USB thing: USB bridge things are often consumer grade devices, and
> > while they may "work" in the sense that you can get a packet in and out, I
> > would not necessarily expect them to behave sanely under any nontrivial load.
> > The same way I would not expect to run a cluster on a $50 Ethernet switch.
> 
> True. We have some USB dongles we've used with CHARON-VAX for years
> without incident, but I don't even know if these are the same brand
> dongles. Even if they are, that doesn't mean anything, of course.
> 
> I'm not a hardware kind of guy, so I tend to miss some of the obvious
> things, like remembering that the "dedicated card" is a USB dongle of
> unknown make. ;-)

I agree with Paul completely here and I wonder, at least for the sake of proving 
the USB device is or is not a factor, why not merely share the host system's 
primary LAN.  Nothing special to get this to work except changing the 
ATTACH XQ argument in the configuration file.  When using that LAN interface,
without jumping through hoops configuring internal bridging, the host won't
be able to talk to the simh VAX instance, but I suspect that may not be a high
priority.

> So I took it down again and did SET THROTTLE 80%.  Still considerably slower, 
> but workable. And as soon as DECnet started, it lost communication and 
> re-established it. It's now two minutes farther into the boot with no further 
> drops.
>
> It drops between the "Starting DECnet" OPCOM message and the first 
> "adjacency up" OPCOM message. After that, all is well.
 
I would be quite surprised if a USB LAN device actually provided reliable 
status/statistic information to the host it is connected to beyond the
basics of link connection state and/or speed settings.

- Mark