[Simh] The Ultimate SIMH VAX Networking Challenge!

[Hans Rosenfeld]

On Sat, Jul 04, 2009 at 02:49:31PM -0700, Seth Morabito wrote:
> 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.

Create a pair of tap devices with taptap for each SIMH VAX. All those
tap devices need to be "up" without any addresses assigned. Bridge all
the even-numbered tap devices with eth0, and attach each SIMH VAX to a
differen odd-numbered tap device.

> 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.

eth0: up
tap0, tap1: up
tap2, tap3: up
br0: eth0, tap0, tap2
br0 192.168.0.100 up
attach 1st SIMH to tap1
attach 2nd SIMH to tap3

Of course, if you want the emulated systems to be reachable from outside
of your local net, you will need to get some offical IP addresses for them.

> 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.

I always assigned the address formerly assigned to eth0 to br0 on Linux,
but I don't know if that makes the difference.

> 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!

I run a similar setup with 2 SIMH PDP-11, 1 P11 and 2 KLH10 on NetBSD.


Hans


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