[Simh] Klh10 vs Simh

[Johnny Billquist]

I must admit that my WiFi knowledge is a bit sketchy, but on the other 
hand do I think that I know ethernet...

But reading up on 802.11, I don't see what you mean by 802.1. I'm not 
even sure what 802.1 actually says.

However, 802.11 uses 802.2 for packets, which is unlike ethernet, which 
is not an 802 protocol at all.

Also, reading up on 802.11, it appears that source and destination MAC 
address are always present. However, there are potentially two more MAC 
addresses in the packet, which I have not found much good information 
about yet. Wikipedia suggest the third is for filtering purposes, and do 
not even explain the fourth one.

What I do know, from observation, is that if I have something like simh 
setup to communicate over WiFi, packets do get sent out, but my simh 
instance will not receive any unicast packets to it, which suggests that 
the switch do not send such packets out over WiFi to the correct 
destination. I would assume it is because switches knows which stations 
actually do exist, but that is a guess on my part.

	Johnny

On 2016-02-28 07:29, Peter Svensson wrote:
> Hi all,
>
> The answers given last time were not all that accurate. WiFi for
> historical reasons conserve bandwidth by assuming that the client side
> 802.11 mac address is the same as the 802.1 sender mac address and thus
> omits the latter. This is the so called 3-address mode. This does not
> leave any room for more than one 802.1 mac address on a client.
>
> However, there is also a 4 address mode for WiFi which does support
> bridging since the 802.1 frames are transported verbatim. This mode has
> many different names from vendors. Most commonly it goes by the name
> WDS, but that name is unfortunately also used by a bunch of non
> transparent mechanisms from other vendors.
>
> See e.g. http://linuxwireless.org/en/users/Documentation/iw/
>
> 802.11 does not care about broadcast one way or another. It is just
> transported. It does not care what layer 3 is used (except only one
> layer 2 sec address in 3 address mode).
>
> The decision to save 6 bytes is an unfortunate historical artefact. The
> (802.11 standard) option to not save these bytes is not always exposed
> on wifi equipment. Some does, and most can I'd you run OpenWrt or
> similar software on them. Not sure about Windows though.
>
> Peter
>
> On February 27, 2016 11:01:31 PM GMT+01:00, Johnny Billquist
> <bqt at softjar.se> wrote:
>
>     On 2016-02-27 20:14, Andreas Davour wrote:
>
>         On Sat, 27 Feb 2016, Johnny Billquist wrote:
>
>             On 2016-02-27 17:53, Michael Kerpan wrote:
>
>                 It's not that multiuser is impossible using KLH10
>                 networking emulation
>                 and native TOPS-20 TCP/IP, it's that it's a lot harder
>                 to set up than a
>                 SIMH virtual multiplexer. Wifi (under Linux at least)
>                 doesn't play all
>                 that well with bridging and virtual networking stuff,
>                 which makes
>                 setting up networking in KLH10 nigh impossible for those
>                 of us stuck on
>                 wireless. I can't even really set up a VM and run KLH10
>                 in a guest,
>                 because Virtualbox's bridged mode doesn't work for me.
>                 Additionally, the
>                 idea of putting anything running a 30 year old TCP/IP
>                 stack onto the
>                 Internet scares me, even if the folks at twenex.org
>                 <http://twenex.org> <http://twenex.org>
>                 have done so.
>
>
>             The WiFi problem is easy to solve. It's called a router.
>             Your host
>             routes IP between the WiFi interface and the virtual network
>             the host
>             and your virtual machine shares.
>
>             Trouble setting up networking on the virtual machine? Maybe.
>             But this
>             boils down to - if you want to run that host, you should
>             learn how to
>             manage it.
>
>             Security issues are mostly non-issues. How many script
>             kiddies today
>             even know what a TOPS-20 host is. There are most certainly
>             vulnerabilities, but they are very different from the ones
>             presented
>             by modern machines.
>
>             I have an RSX system on the Internet, and it gets constant
>             probing
>             over telnet and http, but they are all probing in ways that
>             just don't
>             make sense. So I have never felt more secure.
>
>
>         To Johnnys suggestions I might add that (I don't know exactly what
>         problems you're having) maybe openvswitch might help out?
>
>
>     The problem is that WiFi is not really like ethernet (I think we covered
>     this a month ago, but maybe it was on a different list). Anyway, if you
>     have a simh instance using WiFi for the network, it do not work, since
>     putting the interface in promiscuous mode, and pretend you have a second
>     machine with a different MAC address do not work, since with WiFi, the
>     base station actually knows which MAC addresses are connected, and if a
>     packet comes in for a device for which the MAC address is not
>     registered, the packet will not be send out over WiFi, so you will not
>     get anything, even though you think you have your
>     interface in
>     promiscuous mode, and are sending packets out with a different source
>     MAC address, which you might think the WiFi switch would learn, as it
>     would had it been ethernet.
>
>       Johnny
>


-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol