[HECnet] Same MAC address on different nodes

[Jean-Yves Bernier]

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.

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?

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.


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?


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.



-- 
Jean-Yves Bernier