[Simh] Networking through multiple layers of emulation

[Susan Mackay]

Larry and others who have responded to my posting.

Just to get it out f the way, I'm using this rather complex  
arrangement because the last time I used the 'simh' program directly  
under OS X, I couldn't communicate with the host computer - and I  
don't have another computer I can use to access it. I tried using the  
Tap/Tun method but that doesn't seem to work (or at least I couldn't  
get it to) under OS X.However Parallels allows me to talk between  
virtual machines and between the VMs and the host - just what I'm  
trying to do. I don't want a VM guest OS like Windows (can't afford it  
just for this purpose) which is why I chose FreeBSD.

I'ved used the TcpDump (thanks for the suggestion neozeed) and I can  
see that the DHCP request is being sent and a response passed back  
from the DHCP server. however it does not appear to be heard by the  
simh/OpenVMS combination as nothing happens after that.

I noticed that the MAC address I set in simh is different to the one  
used by the FreeBSD interface and is different again to the one the VM  
is offering. Finally, the DHCP server device shows a list of the  
addresses it has given, and the MAC address it lists against the  
FreeBSD environment is that of the OS X host, and none of the other  
MAC addresses!!!!!

I'm still trying to learn about this level of networking stuff, but I  
understood that the DHCP messages are transferred using MAC addresses,  
there being no IP address for the DHCP service to talk back to (at  
least at the start of the exchange). If that is so, is there some way  
I can see the MAC addresses that are being passed between OpenVMS/simh  
and the DHCP server? I suspect that something somewhere is giving or  
sending the wrong MAC address and so the response from the DHCP server  
is getting lost.

Of course, if there is a simpler way, I'd love to hear about it. (It  
had better be simple if I'm to understand it!)

Thanks for the assistance.

Susan


On 10/11/2009, at 05:52, Larry Baker wrote:

> Susan,
>
> I'm not sure if your motivation is to study multiple layers of  
> emulation or not.  But, if not, it might be quicker for you to just  
> run SIMH directly on your Mac.  Many of us have compiled SIMH for  
> Macs to run OpenVMS.  Give it a try.
>
> Larry Baker
> US Geological Survey
> 650-329-5608
> baker at usgs.gov