[Simh] Using TAP/TUN

[Michael Bloom]

I've started looking a little deeper,  and the first thing I found is 
this from linux-source/Documentation/networking/tuntap.txt:

    4. What is the difference between TUN driver and TAP driver?
    TUN works with IP frames. TAP works with Ethernet frames.

So it would seem that to get the desired multi-protocol generality, one 
would want to use the TAP ioctls not the TUN ioctls that tunctl.c uses.  
Meaning to support non IP protocols, the example in 0readme_ethernet.txt 
would need to change to use a "tapctl" program rather than the tunctl 
program it currently uses (or tunctl could be made into a more generic 
tuntapctl program).  Or perhaps it somehow works as desired right now, 
in spite of the available documentation.

I downloaded the uml_utilities  source, and unfortunately, the code 
contains precious little commenting other than "Licensed under the GPL" 
and no documentation.  So figuring it out may take a little time.

There is a "uml_switch" program.  If we're lucky, this may be a network 
switch in software.  Unfortunately, it uses the TUN ioctls, so if it is 
a switch it would need reworking to use TAP ioctls for it to be an 
ethernet switch rather than an IP switch.  If only it were commented, I 
could say more at this time.

- Michael


On 03/05/2012 05:55 AM, Mark Pizzolato - Info Comm wrote:
> That is completely true for IP traffic.
>
> However, the key goal for the simulator level networking is to have
> these simulated systems be able to talk to other real or simulated systems
> in all the ways that they did when they were natively networking.  When
> these systems were in their prime, IP was not the dominant networking
> protocol.
>
> These systems spoke DECnet, LAT, SCS(Vax Cluster Communications), etc.
> All of these protocols were designed around communications on a LAN.
> The 0readme_ethernet.txt document's goal is to try and get a simulator
> to BOTH be able to participate with these protocols on the local LAN
> AND to have the host system be able to also communicate with the host
> System with whatever protocols they may actually share (usually only
> IP these days).
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