[Simh] EXT :Re: simh on RaspBerry Pi

[Timothe Litt]

LAT uses a different protocol ID.  Most of the WiFi stuff knows TCP/IP;
some do the VPN protocols.

LAT uses group multicast - which I doubt many WiFi applications use or
stress.

It's been a while, but I think the story goes roughly like this:

Routers try to partition the network based on snooping IP; DECnet, LAT,
LAD/LAST are not considered.  Because bandwidth is relatively scarce
(less so with 802.11AC, but there are more demands and interference than
ever...), the routers/access points try to partition clients so
bandwidth isn't wasted broadcasting stuff that no-one is listening to. 
But you can't know that unless you understand the protocol; multicast is
one-way at the MAC level.

They're not alone; try running eigrp, gre multipoint, nhrp or even VPNs
(ESP/AH+GRE) on WiFi.  (Not to mention private protocols like ANF10 on
Etherent.)

Typically you might get a connection from a client to a router, but put
a second client in the same WLAN and they can't talk to each-other.

Then the client drivers/hardware know about a MAC address - but add SimH
and each emulator thinks it has one.  Getting more than one thru the
filters rarely works.  So maybe with pcap you can send from the virtual
MAC address - but the return packets don't get back thru the filters.

Some wired switches have similar issues, but they do better at learning
based on MAC addresses.  Bandwidth on copper is cheaper.

I've probably forgotten or blurred a detail - it got to the point where
we accepted that 'it just doesn't work." 

Of course, with enough engineering and opening of black boxes, anything
is possible - in theory.


On 15-Feb-16 13:53, Paul Koning wrote:
>> On Feb 15, 2016, at 1:48 PM, Hittner, David T (IS) <david.hittner at ngc.com> wrote:
>>
>> LAT runs fine over the (wired) Ethernet port.
>> LAT doesn’t run over wireless Ethernet without major help from the wireless hardware or unless it’s tunneled over IP.
> I'm still baffled.  Why doesn't it?  802.11 has the same MAC layer service as Ethernet -- broadcast, multicast, unicast, 48 bit addresses, etc.  What specifically does LAT do that doesn't work on 802.11?  Is it a standards issue, or a case of defective implementations?
>
> 	paul
>
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