15 Jan
2016
15 Jan
'16
4:01 a.m.
On 2016-01-15 03:55, Brian Hechinger wrote:
Well, the routers really only need to support ethernet
and whatever we
make their WAN links. No one else should care. The only thing this
changes for others is which bridge hub they connect to.
Right. As long as they have something they can connect with.
It?s only a small number of people who need to decide
on what this WAN
link is going to be. And it doesn?t have to be the same between any two
hubs. If you want to use Multinet to me (for example) and I want to do
GRE to Paul that really shouldn?t matter.
Does that makes sense?
Yes. Totally. But a couple of years ago, your options were really
limited no matter who you were. Multinet VMS, Cisco GRE, and that was
about it. If people were running something else, you had no options at
all. And that is still true for some people. However, with the pything
decnet router and so on, they now also have an option.
My point is essentially that for many, ethernet was the only reasonable
option for a long time, so the bridge made sense. And it still does for
some. However, where we can run something else, we should. Having a
larger ethernet segment that covers the whole world is not really a
great solution. :-)
Johnny
-brian
--
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
On Jan 14, 2016, at 9:42 PM, Johnny Billquist
<bqt at softjar.se
<mailto:bqt at softjar.se>> wrote:
On 2016-01-15 03:25, Brian Hechinger wrote:
Yes. This is actually just the traditional way networks are designed.
Ethernet is a LAN - as in local. It's not designed for long haul
connections. It only works because the internet today have pretty
amazing capacity compared to the 80s.
But to get a more traditional topology, we need the routers in between
somehow - and the WAN links.
The problem with that have been that much DECnet gear only supports
various links that best would be described as arcane by todays
standards, in addition to the ethernet. How many use X.25 nowadays? Or
synchronous serial lines?
Well, if you were running a Cisco box, you could tunnel DECnet over
GRE. Not everyone have one of those. The other option more "generally"
available was VMS machines running Multinet, as that supported DECnet
links carried over IP.
One option that is slowly becoming more and more plausible are
specific routers, such as Pauls python router, and Rob Jarrats
implementation.
I can now happily add another. I think I found the annoying bug in my
Multinet-compatible DECnet driver for RSX, so now RSX can also haul
long links over point-to-point instead of having to rely on the bridge.
First link, between MIM and LEGATO is up, and looking stable.
More coming, I hope. Steve, how about SG1? ;-)
Peter, would you like a link or two between somewhere at your end and
MIM as well? Maybe less useful, since we already have DIMMA that does
the same.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email:bqt at softjar.se <mailto:bqt at softjar.se> || Reading
murder books
pdp is alive! || tryin' to stay hip" - B. Idol
On Jan 14, 2016, at 8:03 PM, <Paul_Koning at
Dell.com
<mailto:Paul_Koning at dell.com>> <Paul_Koning at Dell.com
<mailto:Paul_Koning at dell.com>> wrote:
> On Jan 14, 2016, at 4:40 PM, hvlems at zonnet.nl
> <mailto:hvlems at zonnet.nl> wrote:
>
> ...
>> Can the bridge program detect whether there are area routers for
>> the dame area at both ends and favor the local one, possibly block
>> advertising of the remote area router?
>
> I tried blocking traffic from a node in one area from getting to
> another
> area, with the exception of packets from area routers.
> Unfortunately, it does not work. DECnet can be clever about local
> ethernet connectivity. If you are on the same ethernet segment, nodes
> can communicate directly with other nodes on the same ethernet segment,
> even if they are endnodes, and this exen extends to nodes on different
> areas. So such filtering in the bridge cause communication to fail for
> endnodes on the ethernet segment, when the destination is on the same
> ethernet, even if in a different area.
DECnet expects a "transitive Ethernet" -- if A can talk to B and B
can talk to C, A must be able to talk to C. That's actually a
common assumption, other network protocols do the same. DECnet is a
bit unusual in that it explicitly verifies this property, at least
for routers -- that's why router hellos have the router list in
them. We put that in because we had run into some defective
Ethernets that were non-transitive, causing very strange misbehavior
until this protocol mechanism was added.
End nodes have an on-Ethernet cache: if X talks to Y and both are on
the same Ethernet, they will do it directly. From the first packet
if there are no routers; after the initial round-trip if there are.
If you create a non-transitive Ethernet -- which is what filtering
does -- this will fail. There is no workaround. If you don't want
all the nodes on an Ethernet to have direct communication, the only
solution is to split it into two separate Ethernets, interconnected
by a router (not a bridge).
And this is what I was (and always have been) thinking. Make
?shorter? ethernet segments that are less geographically diverse. Put
routers between them. That should solve most problems, no?