[Simh] Ubuntu 17.10 and TAP device for SIMH

[Jordi Guillaumes Pons]

> On 9 Dec 2017, at 21:44, Tim Stark <fsword007 at gmail.com> wrote:
> 
> Folks,
>  
> Since I upgraded to Ubuntu 17.10 (now GNOME shell), I had some problems with networking setup. 
>  
> I finally resolved a problem with TAP device because ifconfig display format changed.  I updated my shell script to create TAP0 device for SIMH use.
>  
> With /etc/network/interfaces, I still have some problems with auto br0 or tap0 setup.   Does anyone have good TAP0 setup for that interfaces?
>  
> I successfully installed SIMH 4.0 beta and noticed that new VDE facility (virtual distributed ethernet). That is very new to me.
>  
> Does anyone have any experience with VDE?  VDE vs TAP?
>  
> For 4K monitor users, login with Xorg and use ‘xrandr –output DP-1 –scale 0.5x0.5’.

Hello Tim,

All my simulated VAXen and PDP11s use VDE since it was available. I’m also using VDE for KLH10 (the “current” source tree also supports it).

Theoretically, VDE puts more load onto the host OS and the network throughput is somehow lower, but in my opinion the flexibility it provides offsets those inconvenients. For instance, I can “plug in” the VDE virtual switch from my laptop using vde_cryptcab, so I can have “mobile DECNET” :)

As an example, this is the /etc/network/interfaces of one of my machines (a Cubietruck ARM SoC running ARMbian, a Debian derivative):

auto lo eth0
iface lo inet loopback
#iface eth0 inet dhcp

auto tap0
     iface tap0 inet manual
     vde2-switch -t tap0 -n 16 -s /tmp/vde.ctl -M /tmp/vde.mgmt -m 666 --mgmtmode 666
           
auto br0
        iface br0 inet static
        address 192.168.0.12
        network 192.168.0.0
        netmask 255.255.255.0
        broadcast 192.168.0.255
        gateway 192.168.0.128
        dns-nameservers 192.168.0.128 192.168.0.12
        bridge-ports eth0 tap0
        up    sysctl net.ipv4.conf.br0.proxy_arp=1
        up    ip link set dev $IFACE promisc on
        down  ip link set dev $IFACE promisc off            

This setup makes an ethernet bridge with static IP address, plugs in the real ethernet interface and a tap one, and creates a vde virtual switch plugs to tap0, so to the bridge. Then I simply attach the SIMH simulated NICs to /tmp/vde.ctl and have all of them visible in my network (no routing setup needed in the hosts).