[HECnet] Same MAC address on different nodes

[Johnny Billquist]

On 2014-05-24 23:14, Jean-Yves Bernier wrote:
At 10:21 PM +0200 24/5/14, Johnny Billquist wrote:

So "Physical" is not "Hardware", and there is no need to SET XQ MAC.
I tried and it maked no change.

Right. Since your machine will set a different MAC address anyway, at
start, when you enable DECnet. The physical address is whatever you
set in simh before starting. It have no actual relevance once DECnet
starts. If you were to run something else, which did not use DECnet
(such as Unix), the address you set in simh will be the actual MAC
address used, since IP do not change the MAC address of interfaces. No
need.


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).

The MAC address is AA-00-04-00-01-28 for DECNET and 08-00-2B-AA-BB-CC
for Linux.

Uh... Not really. simh do not actually change the MAC address of the physical interface.
What it does is that it "fakes" it, so that you get a second MAC address on the physical interface, which just leads into simh. Linux own MAC address is yet again something else, and that is never touched.
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.

And with "physical" here I mean the actual network card in your PC, which Linux (or whatever host) is using.

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.
So, if you in Linux runs both DECnet and TCP/IP, you'll have a different MAC address than if you were to only run TCP/IP.

Really hard to give a good explanation on why without having good
access to all parts of the setup to be able to test and examine things.

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

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

	Johnny

-- 
Johnny Billquist                                   || "I'm on a bus
                                                                  ||   on a psychedelic trip
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