[Simh] Vax.exe emulator and Multinet network configuring

[Johnny Billquist]

On 2019-05-10 02:01, Paul Koning wrote:
> 
> 
>> On May 9, 2019, at 7:55 PM, Johnny Billquist <bqt at softjar.se> wrote:
>>
>> On 2019-05-10 01:46, Paul Koning wrote:
>>>> On May 9, 2019, at 3:20 PM, Hittner, David T [US] (MS) <david.hittner at ngc.com> wrote:
>>>>
>>>> (It's been a long time since I've played with SMAC on wireless. I did get it to work, but it wasn't worth the pain to me, so I upgraded to DECNET/OSI non-compatibility mode.)
>>>>
>>>> IIRC, when you start DECNET IV, it sends a broadcast packet to see if there is an address collision with the hard-coded DECNET IV address before it changes the MAC to the DECNET IV MAC.
>>> That's not in any DECnet standard.  It may be someone did that, and it wouldn't be a bad idea to do so.
>>> BTW, some NICs allow enabling multiple individual addresses and choosing which one you want.  DEC made that standard fairly early on, once it became clear that combining LAT and DECnet on a single interface was a pain.  DEUNA doesn't do this, DEQNA does, and all the DEC single-chip Ethernet interfaces support it.  On such interfaces you'd use the aa-04 address for DECnet and the "hardware address" for other things.
>>
>> Hum? My understanding is that the DEUNA and DELUA works exactly the same in this aspect. And combining DECnet and LAT is not a problem on of those interfaces, so now I'm curious what you are thinking of?
>>
>> Also, at least under RSX, all software is definitely using the same MAC address for any and all network protocols you might be running, which includes DECnet, LAT, MOP, IP, ARP, and anything else you might want to throw at it.
> 
> That's certainly allowed, but as I said, most DEC NICs allow you to avoid the DECnet address for other protocols.
> 
> The difficulty was with VMS, which would start LAT before DECnet and use the hardware address for LAT if the individual address hadn't been overridden.  So your sessions would fail because the address would change.  The solution, with the DEUNA, was either to start LAT after DECnet, or to teach VMS the DECnet address via some other system parameter so it would be set at boot time, not wait until DECnet startup.  The multiple individual address feature was made a standard part of the DEC Ethernet architecture so you wouldn't need to do any of this; if a protocol needed a specific format address it could just use it, without bothering other protocols on the same machine.

Ok. Yes, changing the MAC address is always a potential problem.

But I wonder if you are mixing controllers up. I just re-checked the 
DELUA manual, and it only allows one physical address. You can change 
it, but there can be only one, and if you want to receive any others, 
you'll have to go into promiscuous mode. It allows up to 10 multicast 
addresses.
And this is just the same as for the DEUNA.

Maybe later DEC controllers allowed more, but as far as I know, the 
DELUA do not.

Also, the DEUNA and DELUA does not allow you to set the source MAC 
address on transmitted packets. You need to have the room for it, but at 
transmission, the controller will on its own insert the actual physical 
source address in the transmitted message. So it's probably totally 
impractical/impossible to use several MAC addresses, even if you were to 
enable promiscuous mode. Promiscuous mode can be used to get packets on 
the ethernet, but you still can't act as if you have multiple MAC 
addresses. And changing the MAC address is a very disruptive process 
that you cannot really be doing during normal operation.

I should probably go and dig some in VMS, but my recollection is that 
the address changes halfway through the booting, and for that reason the 
network goes down and up again during booting, and other protocols like 
LAT handles this. But I might be misremembering things in VMS. I use it 
too seldom these days...

   Johnny

-- 
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