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I am running some SIMH emulators (think of them as vintage computer virtual machines) on a Raspberry Pi running Raspbian buster, and I'd like to set up networking so that a two-way connection with the outside is possible. For the record, I'm only using Ethernet (no WiFi) on a RPi 1.

In order to do that, a guide [1] suggests to create a tap interface to which the VM will connect, assigning it an IP inside the home network, and bridging it with eth0. However:

a) buster apparently ignores the /etc/network/interfaces initialization routine, so I can't use the kind of config script described in the guide

b) if I set up a tap interface manually with ifconfig tun0 192.168.1.88 up (as an example, not the same IP as the RPi), the ssh connection to the Raspberry Pi freezes and it basically stops responding to the network until I connect via serial terminal and take tap0 down

So my question is, what's the most appropriate way to create such a configuration, in which the VMs running inside the RPi have two-way access to the network (at least home network, ideally also to the outside world), in a way that's also respecting of buster's conventions for init scripts?

[1] - https://mansfield-devine.com/speculatrix/2016/03/networking-vax-openvms-on-simh-the-raspberry-pi/

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  • I can't answer your specific Question, but Raspbian-Buster still has Debian networking, and you can revert to this if you wish. How to set up Static IP Address explains how to disable the DHCP client daemon
    – Milliways
    Commented May 10, 2020 at 0:08
  • Any hypervisor/emulator like KVM, or QEMU, or Virtualbox, or XEN, or LXC, or what else, has its own network interface to the guests and they all describe it in its documentation. So you should have a look at the documentation of your SIMH emulators.
    – Ingo
    Commented May 10, 2020 at 11:15

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Current versions of SIMH don't need setting up tun/tap interfaces in order to be able to use TCP/IP with them, as it provides a nat: network interface that does all the work for you of setting up NAT to work with your emulated machine [1]

Just attach the guest's NIC as follows:

       sim> attach xq nat:tcp=2323:10.0.2.15:23,tcp=2121:10.0.2.15:21

and it'll even deal with port forwarding for you.

[1] https://github.com/simh/simh/blob/master/0readme_ethernet.txt (lines 184-215)

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