[HECnet] DECnet et al

[Johnny Billquist]

On 2011-07-17 19.53, hvlems at zonnet.nl wrote:
Ennodes only become clever when the first datagram from the remote host returns. After that unnecessary routers are bypassed. Perhaps phase IV+ is different, in phase IV the first packet to a host outside the area is always sent to a router, when present.

It's the same inside the area. Endnodes maintain a cache of DECnet nodes it can communicate directly with, and bypass routers for those destinations. No matter what area. And it does this wether a router exists or not.

For everything not in the cache, the designated L1 router is used. It might be, however, that if no router exists, it just chances and tries to communicate directly anyway, even without a cache entry, since it has nothing to loose.

But if we skip L1 routers, then we loose all communication within the area as well, if it is formed by more than one segment. And still, all L2 routers are also L1 routers.
And I'm pretty sure an endnode will not use a L1/L2 router in another area as its designated router.

So skipping routers will reduce functionality in severe ways. But the need for plain L1 routers are perhaps not that big. But they might still have their use.

There exists also one problem not mentioned here, in connection with my bridge program. Machines have limits on how many broadcast endnodes and routers are handled on one ethernet segment. As we grow my virtual ethernet segment, we'll start hitting problems here. We might eventually want to split this into two different segments, with a router in between...

	Johnny

Verzonden vanaf mijn draadloze BlackBerry  -toestel

-----Original Message-----
From: Johnny Billquist<bqt at softjar.se>
Sender: owner-hecnet at Update.UU.SE
Date: Sun, 17 Jul 2011 19:40:10
To:<hecnet at Update.UU.SE>
Reply-To: hecnet at Update.UU.SESubject: Re: [HECnet] DECnet et al

On 2011-07-17 17.30, hvlems at zonnet.nl wrote:
Bob, endnodes in different areas can only talk to each other if there's no router present. So your scheme only works if all of us shut down all our L1 and L2 routers. Once an endnode sees a router in its area it will send all its off-area datagrams to it. If that router is an L1 router then the other area is seen as unreachable. If it is an L2 router then it must see the other area router.

No, endnodes will be clever and directly talk to other nodes that are
directly connected, even in the presence of a router. But the router is
needed to talk to anything not directly connected.

	Johnny


I do need L1 routers (for DDCMP and DSSI circuits) and possibly others do too.
Show net/old is neat and useful when systems are in different rooms !
Hans
Verzonden vanaf mijn draadloze BlackBerry  -toestel

-----Original Message-----
From: "Bob Armstrong"<bob at jfcl.com>
Sender: owner-hecnet at Update.UU.SE
Date: Sun, 17 Jul 2011 08:21:12
To:<hecnet at Update.UU.SE>
Reply-To: hecnet at Update.UU.SESubject: RE: [HECnet] DECnet et al

Yes.   But any L1 routers need help from L2 routers to get out of area.

      Yeah, but given that the routers aren't actually needed for two nodes to
talk (under HECnet circumstances) then we don't actually need the routing
nodes at all.   Sounds like their only real use is to be able to do a "SHOW
NETWORK/OLD" and see an nice list of active nodes (which is undeniably
neat)...

      So a node configured as an end node in area 'n' can actually communicate
directly, over Ethernet, with another end node in area 'm'?   But a L1
routing node in area 'n', in the same physical network topology, would
actually relay its packets for a node in area 'm' via an L2 router?   And
does this actually take two L2 routers to hand off the packets, one for area
'n' and one for 'm'?

    So (again, in the HECnet situation only) having an L1 router is a real
penalty - where as two end nodes could talk directly, just changing the same
machines to L1 routers would require the same traffic to be handled by two
intermediate nodes.

      Or an I confused?   That's a bit bizarre.

Bob