[HECnet] Same MAC address on different nodes

[Johnny Billquist]

On 2014-05-25 15:53, Jean-Yves Bernier wrote:
At 9:26 AM +0200 25/5/14, Johnny Billquist wrote:

You mean "the Hardware address is whatever you set in simh before
starting". CEX will set it to "Physical address" (in DECNET parlance)
which is AA-00-04-00-(1024 x area + node).

Uh... Not really. simh do not actually change the MAC address of the
physical interface.

Of course, simh don't do DECnet. Communication EXecutive does.

Right. But the communication executive does it by programming the ethernet interface, which get down to a command into simh...

The simh interface starts out with 08-00-2B-AA-BB-CC, but that is
changed to AA-00-04-00-01-28 by DECnet when it starts up, at which
point it no longer listens to 08-00-2B-AA-BB-CC. That address is just
kept around as the original hardware address of the simulated network
interface inside simh.

So we have:

Executor node = 10.1 (SHARK)
    Physical address = AA-00-04-00-01-28
Line = QNA-0
    Hardware address = 08-00-2B-AA-BB-CC

Executor node = 10.2 (SNAKE)
    Physical address = AA-00-04-00-02-28
Line = QNA-0
    Hardware address = 08-00-2B-AA-BB-CC


We still have the question "when two nodes runs on the same host, is SET
XQ MAC" necessary? In other words, does the "Hardware address" play any
role in DECnet, besides just being kept around?

No role at all.

Since it would be pointless to put the same address, i tried

SET XQ MAC==00:00:01:00:00:01/02, then

Executor node = 10.1 (SHARK)
    Physical address = AA-00-04-00-01-28
Line = QNA-0
    Hardware address = 00-00-01-00-00-01

Executor node = 10.2 (SNAKE)
    Physical address = AA-00-04-00-02-28
Line = QNA-0
    Hardware address = 00-00-01-00-00-02

And I see no difference.

Because it won't any difference. :-)

So, a NIC may have different MAC addresses depending of the network
stack running. Am I right here?

Sortof. Your machine normally do only have one MAC address, but if you
have DECnet running, it will need to change your MAC address. All
other network protocols on your machine will then also use this "new"
MAC address.

If we would run on bare metal. They don't because simh shields it. Maybe
the "Physical address" is kept just for restoring it at shutdown?

Not even that. The physical address is in a PROM on the ethernet card. Any resetting of the bus, and the ethernet card reverts to the address stored in the PROM. (Or whatever you set it to, if we talk about simh.)

Well, my system is working 99%, that's not so bad :)

It is working 100%, you just have performance issues...

Besides playing around, which I admin is awfully fun, the reason for
using DECnet was to transfer big files (tens of megabytes). So I am out
of luck for now, but I haven't said my last word.

Like I said before. I would start by examining various counters on the machines to get more understanding of what the problem is, and then try to solve it from there.

I know that different network interface speeds mess things up, for example, and I have code in my bridge to help get around the problem if the bridge is sitting between the systems.

	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