[HECnet] DECnet Phase IV through Linux GRE Tunnel?

[Johnny Billquist]

On 2018-01-07 02:30, Supratim Sanyal wrote:
> On 1/6/2018 20:20, Johnny Billquist wrote:
> 
>> We could, in theory, connect them all using the bridge as well. But 
>> it's not a good idea. DECnet does not scale well in that way.
>>
>> Security is not the biggest issue.
> 
> True that. I know first-hand what a mess packets looping back over 
> ethernet can be.

Not the only problem either. DECnet over Ethernet means all routing 
nodes needs to keep track of all other routing nodes on the ethernet 
segment, and they all broadcast packets at regular intervals. And so, 
DECnet have a limit on how many routing nodes can be on a segment, which 
is somewhat limited. And all nodes (even non-routing ones) broadcast 
packets at regular intervals.
And even nodes from different areas take shortcuts with ethernet 
sometimes, not even going over routing nodes when talking on the same 
ethernet segment.

All in all making it starting to look pretty bad when you get too many 
nodes on one ethernet segment.

Packet looping in ethernet is not DECnet specific, and is the reason why 
switches implement STP. I was just too lazy to do that with the bridge 
program. ;-)

> Still, Mark could patch in all simulated nodes and bridge in all 
> physical nodes to a VDE switch for local DECnet traffic, and use a 
> router SIMH node for Multineting to MIM ...

Or just use an actual ethernet switch, since he'll need one for the 
physical machines anyway.

In the end, he need a router in order to keep local traffic local. And 
the router will have one interface towards the local side, which needs 
to get on to an ethernet switch in order to connect physical machines 
anyhow, and one interface towards the rest of HECnet, in which case a 
Multinet link is just as good as anything else, and already is known to 
work, and can be done with the equipment he has at hand, if he just 
installs VMS Multinet.

   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