[HECnet] Others DECnets

[Johnny Billquist]

Hi.

Paul Koning wrote:
-----Original Message-----
From: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] On
Behalf Of Johnny Billquist
Sent: Friday, December 04, 2009 6:49 AM
To: hecnet at Update.UU.SE
Subject: Re: [HECnet] Others DECnets

Hi.

Steve Davidson wrote:
They used to call that poor-mans-routing (PRM), and yes that is
basically how it worked.   ZKO has over 3000 machines and only had
areas
2 and 19.   The fix was hidden area support which in this case meant
anything from either 63, or 62.   I don't remember if they used areas
61
or 60.   I managed machines in area 2, 19 and 63.   My area 63 nodes
were
on satellites of clusters (in either area 2 or 19) that has DECnet
aliases   Worked very well.   For those who were unfortunate to not be
attached to a cluster PMR was the only way to either send mail, or
SET HOST.

Yes, PMR is "well known". :-)

I think I can see how the hidden network idea can work now.
The level one router just needs to have two separate network
interfaces,
and two separate physical networks, and then it could work.

The reason it will work is because DECnet can do a shortcut in some
places, one of them being that a level one router can actually talk
directly to a level two router in another area.
That doesn't sound right.   A level 1 router doesn't listen to area route
messages so it doesn't know anything about other areas, or area routers.
Only area routers do such a thing.

Yes. I agree. And I was kindof surprised that they actually do this, but I seem to remember discovering that they actually are doing this as I was trying to isolate areas with my bridge program. My problem was that I set up a filter which prevented traffic from generic machines in one area to send packets over the bridge, only allowing specific machines (level two routers in my case). The experimentation failed, since broadcast messages still were allowed to spill over, and I discovered that machines tried to talk directly with eachother without going through the level two router.

So that idea failed. :-(
But I learned something...

I don't remember the actual setup that was used, but I *think* it was
like this:
The network backbone was built out of area routers that had their max
area set to 62 (or whatever was the highest "real" area).   Any area that
contained hidden-area nodes would connect to the backbone with another
area router (or set of them) which have max area set to 63, and all the
other nodes in that site would only connect to these max-63 area
routers.   Those area routers could see the local area 63, but the
backbone could not because that's outside the range of area numbers it
was supporting.
So routing works.   Say that node 2.2 wants to talk to 63.123.   Assume
both are L1 routers for simplicity.   2.2 would send to its nearest area
router, which (by the config rule) has max area 63.   So it knows how to
get to the area 63 router.   That path is guaranteed not to involve any
backbone routers because those have max area set to 62 so they aren't
offering any path to area 63.   The packet gets to the area 63 router,
which delivers to 63.123.   The same works in the other direction.

Hmm. That was another intriguing idea... Gotta think a little bit more here.

I only know stuff from what I've observed here. I haven't actually tried making any "hidden" areas.

My effort was basically motivated by my trying to reduce traffic over the bridges, since I could configure my bridge to tell which machines were actually making meaningful data to really pass over the bridge.
I'll be happy to explain in more detail how and why this failed, if people really want to know.

	Johnny

	paul