17 May
2024
17 May
'24
2:50 a.m.
On May 16, 2024, at 4:47 PM, Johnny Billquist
<bqt(a)softjar.se> wrote:
DECnet addresses are AA-00-04-00-xx-yy, which I'm sure most people are aware of. As
such, as long as each machine has it's own DECnet address, they will also have their
own MAC address. The question is, though, if KLH handles this completely transparent to
you, or if you need to do some things yourself here. For other simulators, it sortof
depends on the host system and your setup, and so on, since there is no standardized API
under Unix (or Windows, I believe) to set the MAC address on an interface. But there
sometimes do exist an API for it.
FYA, internally that scheme was sometimes referred to as "Bernie LaCroute's
hack" after the VP who insisted that using real 48 bit addresses was too hard.
For real hardware, the network interfaces do have a
MAC from the factory, but it's also stated in the standards that ethernet interfaces
should support software changing the MAC address of the interface. And that is what DECnet
normally does, and all DEC ethernet interfaces certainly allows this to be changed.
Not only that, most DEC LAN NICs supported multiple individual addresses per NIC, so you
could start up the system with LAT or IP enabled (bound to the default MAC address) and
then afterwards start DECnet Phase IV and have it use the Bernie address only for its use,
i.e., for traffic on protocol type 60-03. I'm not sure all OS supported this, and
early hardware didn't, but the QNA could and all DEC internally designed silicon could
as well.
And that means any emulator/simulator also gets
informed about the MAC address change, since the OS running on the emulator will poke at
the controller for it to change the MAC address to whatever DECnet needs it to be.
The question is then, what does the emulator/simulator do when this happens?
Johnny
On 2024-05-16 22:41, Thomas DeBellis wrote:
> On a KL emulation running Tops-20, if you want to run Phase IV, you have a choice of
the CI or NI. In order to not implement ARP for DECnet, they came up with the idea of a
certain range of 48 bit MAC address having a direct mapping.
> For the CI, this is built off of the CI interface number and there is no getting
around that, as I recall. For the NI, it wants to pick the MAC address. You can get
around this by knowing what MAC address it will pick and configuring that. It's
sometimes easier to just spend the $15 and get another USB interface and dedicate it to
the engine.
Interesting. I never heard of any spec for DECnet over CI. DECnet supported any number
of quite obscure devices, from PCL-11 to 802.5 token ring (sort of), but not CI in any
document I have ever seen.
paul