[Simh] VMware "internal network" and VAX mop frames

[Paul Koning]

> On Feb 21, 2018, at 9:08 AM, Timothe Litt <litt at ieee.org> wrote:
> 
> I can't think of anything that would fail if the ROM address is the same as the DECnet address (which is what you're setting up), but no real hardware could ever have been configured that way.  (It is possible for software to obtain both, though only one goes on the wire.  One set by software overrides the ROM, which is globally unique.)

Most of the later DEC NICs support multiple MAC addresses, with the ROM address as the default.  On such NICs, MOP and LAT (and possibly other protocols) use the ROM address, while DECnet Phase IV would use the HIORD style address.  A few older NICs, for example the DEUNA, don't have this capability and for those the MAC address changes for everyone as soon as you turn on DECnet.

> ...
> I'm not a VMware user, so they may use different terminology than the following.
> 
> So VMware would need to understand that a MAC address can be changed - more recent OSs don't set the MAC address, so it could be confused.  I wouldn't be surprised if it acted like a switch & tried to filter "unneeded" packets.

That's definitely a possible issue.  Another possibility is that multicast isn't supported properly.  All NICs support broadcast, because otherwise IP would not work, but multicast is not so commonly used.  DECnet uses it everywhere, though, and requires it to be there.

I remember some discussions about trouble if you use a wireless LAN as opposed to a wired NIC, but I don't remember any details.

	paul