[Simh] The Ultimate SIMH VAX Networking Challenge!

[Seth Morabito]

Hey everyone,

I've got a puzzler for the more experienced SIMH users here who might
already be doing what I'm trying to do.

My end goal is to have a single host system, with a single physical
Ethernet, hosting two (or more!) SIMH VAX instances. Each SIMH VAX
should be able to communicate with all the others, and with the host,
and all of them should be reachable from the public Internet.

So, for a concrete example: Assume the host has a single ethernet,
eth0, with address 192.168.0.100. The two simulated VAXen should have
addresses 192.168.0.101 and 192.168.0.102, and be able to communicate
with the host, with each other, and with anything else on the
192.168.0.0/24 network.

I've been trying to wrap my head around various techniques using
taptap.c and bridge-utils, but I have been frustrated getting anything
to work.

For reference, here are the pages I've been studying:

http://www.retrocomputinggeek.com/retrowiki/SIMHNetworking/
http://www.itsecuritygeek.com/itsgeek/comments/simh-modified-version-of-taptapc/

The technique of using taptap.c works well for host-to-SIMH
communication, but the VAX is not routable to the outside world since
it needs to be on its own network. Conversely, trying to use
bridge-utils to create a tun0/eth0 bridge just causes the host to
become unrechable on eth0's IP address (quite alarming when I was
trying to set up the bridge remotely, and ssh simply froze up after
adding eth0 to the br0 bridge!), so I've had no luck with that at all.

Has anyone had success doing this? I've been searching for a solution
for a couple of days now, I've lost hope that it can actually be done!

-Seth
-- 
Seth Morabito
Union City, CA, USA
sethm at loomcom.com