[Simh] MicroVax 3900 Networking on a Macbook Air

[Jordi Guillaumes i Pons]

> 
> Johnny's comments and suggestions are right on.  
> 
> One way to help get you there might be to use VDE networking. Some folks have used vde for various purposes.  If someone who uses VDE networking provides some guidance we can add more vde specific information to 0readme_ethernet.txt.

I wrote this guide some time ago. 

http://ancientbits.blogspot.com.es/2012/06/simh-39-using-vde-for-fun-and.html

It is oriented to debian-style Linux distributions, but can be easily adapted to OSX, given:

- You need to install the tuntap drivers. http://tuntaposx.sourceforge.net/download.xhtml

- You will have to write a shell script to set up the network “on demand”. In the post I write about setting it up automatically at startup.

- The bridging setup is different in OSX. Instead of using brctl to set up the bridge and attach interfaces to it, in OSX you use simply ifconfig. For instance, to set up a bridge and add tap0 and en0 to it:

sudo ifconfig bridge1 create
sudo ifconfig bridge1 up addm tap0
sudo ifconfig bridge1 up addm en0

To put down the bridge:

sudo ifconfig bridge1 destroy

(The idea is to attach the VDE virtual switch to tap0, and then bridge tap0 to en0 so the packets appear both in your WIRED ethernet and your virtual switch).

- If you don’t wat to set up a bridge, you’ll need to enable IP forwarding. Add this line to /etc/sysctl.conf and reboot (or source it): 

net.inet.ip.forwarding=1

Note this will enable to reach your virtual vax using TCP/IP but not DECNET; to use DECNET you have to set up a bridge, or to tunnel the DECNET packets using Johnny’s bridge or a VDE ssh tunnel (as shown in the blog post). IIRC the current versions of simh do have builtin support of Johnny’s bridge “procol” under the XQ device. (attach it to udp:ip_address:port to set it up, and set up the “real” bridge at the other side).

To summarize, step by step:

- Install the tuptap drivers.
- Install VDE using macports or whatever package manager you use.
- Build SIMH with VDE support. Be sure you get the following two lines when you issue the “make” command:

*** - dynamic networking support using OSX provided libpcap components.
*** - Local LAN packet transports: PCAP VDE TAP

- Configure your simh instance to use VDE (vax.ini file):

set xq enable
attach xq vde:/tmp/vde.ctl 

- Start VDE networking:

#!/bin/sh
echo Iniciant switch virtual
vde_switch --mode 666 --numports 8 -mgmt /tmp/vde.mgmt --mgmtmode 666 -s /tmp/vde.ctl --daemon 
vde_plug2tap --daemon tap0

(You need the last line just if you want to set up bridging).

- Set up the bridge as shown before, or set up a vdeplug link using SSH.

I’ve just tested it works under El Capitan as I am writing this mail, and it seems to work OK.

Drop a line if you have any trouble and we’ll try to sort it out!