...
The 2.0.0 (phase IV) routing spec talks about the "on Ethernet"
cache
instead, and describes it in a way that makes it help only for
directly
attached nodes. The "previous hop" flavor was a generalization in,
I
think, 2.1.0 (Phase IV+).
Hmm, yuck. Now I'll have to try to remember some details, as well as
extrapolating some stuff.
No, as far as I can remember, the end-nodes will only remember (or
know)
of one level 1 router. It will pick the one with the highest priority
in
case there are more than one on the local segment. That will become
the
designated router, and will be used for all traffic I believe.
The way this works is that there are two multicast addresses used on
Ethernet segments. (Well, three later on, a separate one for all L2
routers.) One is "all routers", one is "all endnodes". Routers listen
to the first, endnodes to the second. Hellos are sent to "all routers"
so ONLY routers hear hellos. Both endnodes and routers send hellos
(different types). So routers build a list of all the nodes on each
interface. The routers on an Ethernet pick one to be the designated
router, and only that router sends a hello to "all endnodes". That's
how endnodes know the DR.
End-nodes will, however, just snoop hello-messages, and know about
other
nodes that are on the same ethernet segment (I'm not sure if this
generalizes to other mediums than ethernet, I think the manuals only
talked about ethernet). So, you can actually have an ethernet segment
with only end-nodes, and communication will actually work anyway. Even
though if you look at adjacent nodes with NCP, you'll not see any.
That's the ethernet cache unless I read things wrong here, btw.
No, endnodes don't do any snooping (nor do routers). DECnet
intentionally was designed to rely on advertisements (hello messages)
and those were done in a way that limits overhead. So end nodes hear
only hellos from a single system (the designated router).
If an end node is asked to talk to some address, it consults the cache.
If it's in the cache, the data there is used. If not, the message goes
to the designated router if one is known. Finally, if there is no DR
(single endnode-only LAN) then it sends directly to the destination
using the calculated MAC address.
Incoming traffic fills in the previous-hop cache, so once you get past
the first message, end node traffic goes via the optimal path.
What I find "horrible" about this is that end-nodes will (atleast in
VMS) will actually happily even talk with machines in another area, if
they happen to be sitting on the same ethernet segment (this has
bitten
me with my bridge and HECnet).
Yes, that was considered a feature. It's a side effect of the way the
previous hop cache works, and when we realized this we decided it was a
good thing so that's how it ended up.
Anyway, the comment is that the path might not be optimal. End nodes
pick the level 1 router with the highest priority. If you have two
level
1 routers, the one you didn't communicate with might have been more
optimal, but you'll never know. And the same is true for area routers.
For out of area traffic you're definitely right, the first leg is to the
best L2 router for the destination area, which may not be the best way
to get to the final destination. (In a sensibly layed-out hierarchical
network, the difference should not be large.) But end nodes do
communicate just as efficiently as routers, thanks to the previous hop
cache. And in fact, for the multi area Ethernet case, they do better
than routers because routers will not talk directly to an out of area
node, even if it's on the same Ethernet.
paul
Brian Hechinger wrote:
On Mon, Jun 28, 2010 at 12:10:31PM -0700, Johnny Billquist wrote:
Should I just use one area? What's the best way to set that up?
Areas in DECnet are not really meant to be associated with physical location, but rather with organizational. So keep it within one area.
Ok, sounds good to me.
For physically different locations, you might want to use level 1 routers, though. But as the internet nowadays is so fast, using just a bridge, and pretend that it's all one ethernet segment also works just fine.
My upstream blows (as well as latency in general) so I'd like to avoid
putting any more traffic across it than is absolutely nessesary.
In that case you should definitely not use my bridge...
I suppose it's not a huge deal at this point since the SIMH instance at
the colo will be the only thing running most likely for a little while.
That being said, how should I set it up? L1? L2? Does anyone want to
use me as a hub?
L1? L2? As in layers in the network stack?
Also, is there a list of what areas are already in use so I can pick an
unused one?
Already answered by others, I noticed... :-)
Johnny
Paul Koning wrote:
Johnny, the original DECnet manuals showed pictures of area routers
that
were interconnected by WAN links. Each site had its own area number.
In
fact
the name "area routing" implies clearly that the concept was meant to
set up
DECnet networks that were geographically separated.
I don't remember those pictures, but this is an issue that generated a
lot of debate and a lot of annoyance in the DECnet architecture group.
The pictures, atleast in the RSX manuals, are very simplistic. Like five nodes, maybe four areas, and spread between the west and east coast of the US.
...
One reason for separating systems in different areas was that
rebooting
the
pc's would generate so many DECnet state up and down messages that
PDP-
11's
and the older VAX systems choked in their console output.
That's a good one. (Actually, the way to deal with that is to turn the
logging to console off for that event...) Yes, that's a valid example.
The purpose of area routing is to avoid having things get too large.
There were various opinions on how big an area (or Phase III network)
could reasonably be. Originally the limit was assumed to be about 32,
without any basis that I know of. That too produced a pile of debate,
and later on it became obvious you could go much higher. But clearly
you couldn't run a flat Phase III style network with 10,000 nodes.
Well, phase III networks could never be more than 255 nodes. :-)
For that reason area routing was introduced, so each instance of the
routing algorithm (in-area and level 2) would deal with a reasonably
small topology. Again debates broke out whether a full area (1000
nodes) was acceptable. It turned out yes, but certainly keeping it
smaller, say to 100-200, would be a good thing if possible.
When phase IV came, and the node address was extended to 16 bits, it's obvious (I think) that you didn't want a flat 16-bit address space.
So then it becomes a question of how to split that address up. By that time, I think they had come to the conclusion that a single network could definitely be more than 255 nodes. 1023 seemed like a good size, leaving 63 areas. (Neither node 0, nor area 0 is permitted.)
Geography isn't a consideration unless the links are slow enough to make
route change propagation an issue. Corporate organization (different
departments) CERTAINLY isnt' a consideration, though some people tried
to argue that it was valid to do so.
Well, level 1 routers gives you pretty much the same isolation as areas. Unless you consider the relative size of the level 1 routing messages a problematic burden compared to level 2 routing messages. However, I'm not even sure you can make the system not transmit level 1 routing messages on all interfaces, meaning they will go out anyway, even if you only have another area at the other end of the line.
Johnny
Paul Koning wrote:
...
Level 1 routers knows where all machines in the same area are located,
and knows the most efficient way to any node within the same area.
However, it only keeps track of the closest area router, and knows
nothing about any other area.
Area routers work just like level 1 routers, but they also have an
area
routing table, so they know the most efficient path to an area router
for any area.
So, an end node only knows what machines are on the same segment, and
which is the closest level 1 router. Level 1 routers knows where all
machines are in the same area, and knows where the closest area router
is.
Area routers knows where every machine is on the local area, and also
where all area routers are.
Right... except for end nodes. Those know what *routers* exist on the
same segment. End nodes don't know (directly) about other end nodes.
To make that case efficient, end nodes have a "previous hop cache".
Whenever an end node hears from another node, it remembers the previous
hop (the last router on the path) and sends future traffic for that
destination to that router. This way it can pick any router for the
initial packets but will quickly move to the optimal one. It also
tracks directly connected endnodes in that cache, because a router that
forwards a packet onto the same segment as it arrived will leave the
"intra-Ethernet" bit in the header set, which tells the endnode that
destination is directly reachable.
The 2.0.0 (phase IV) routing spec talks about the "on Ethernet" cache
instead, and describes it in a way that makes it help only for directly
attached nodes. The "previous hop" flavor was a generalization in, I
think, 2.1.0 (Phase IV+).
Hmm, yuck. Now I'll have to try to remember some details, as well as extrapolating some stuff.
No, as far as I can remember, the end-nodes will only remember (or know) of one level 1 router. It will pick the one with the highest priority in case there are more than one on the local segment. That will become the designated router, and will be used for all traffic I believe.
End-nodes will, however, just snoop hello-messages, and know about other nodes that are on the same ethernet segment (I'm not sure if this generalizes to other mediums than ethernet, I think the manuals only talked about ethernet). So, you can actually have an ethernet segment with only end-nodes, and communication will actually work anyway. Even though if you look at adjacent nodes with NCP, you'll not see any. That's the ethernet cache unless I read things wrong here, btw.
What I find "horrible" about this is that end-nodes will (atleast in VMS) will actually happily even talk with machines in another area, if they happen to be sitting on the same ethernet segment (this has bitten me with my bridge and HECnet).
Now, this means that a machine that sits in one area will not
neccesarily take the shortest path to a machine in another area. In
fact, it will not neccesarily take the shortest path even to another
machine in the same area. But that's another story. :-)
??? It certainly will, where "shortest" is defined as "least path
*cost*", not necessarily fewest hops.
Sorry. Yes, you are right. I should have been more careful with my words. It was the path cost I was thinking of. I should have said cheapest, not shortest.
Anyway, the comment is that the path might not be optimal. End nodes pick the level 1 router with the highest priority. If you have two level 1 routers, the one you didn't communicate with might have been more optimal, but you'll never know. And the same is true for area routers.
Johnny
...
Level 1 routers knows where all machines in the same area are located,
and knows the most efficient way to any node within the same area.
However, it only keeps track of the closest area router, and knows
nothing about any other area.
Area routers work just like level 1 routers, but they also have an
area
routing table, so they know the most efficient path to an area router
for any area.
So, an end node only knows what machines are on the same segment, and
which is the closest level 1 router. Level 1 routers knows where all
machines are in the same area, and knows where the closest area router
is.
Area routers knows where every machine is on the local area, and also
where all area routers are.
Right... except for end nodes. Those know what *routers* exist on the
same segment. End nodes don't know (directly) about other end nodes.
To make that case efficient, end nodes have a "previous hop cache".
Whenever an end node hears from another node, it remembers the previous
hop (the last router on the path) and sends future traffic for that
destination to that router. This way it can pick any router for the
initial packets but will quickly move to the optimal one. It also
tracks directly connected endnodes in that cache, because a router that
forwards a packet onto the same segment as it arrived will leave the
"intra-Ethernet" bit in the header set, which tells the endnode that
destination is directly reachable.
The 2.0.0 (phase IV) routing spec talks about the "on Ethernet" cache
instead, and describes it in a way that makes it help only for directly
attached nodes. The "previous hop" flavor was a generalization in, I
think, 2.1.0 (Phase IV+).
Now, this means that a machine that sits in one area will not
neccesarily take the shortest path to a machine in another area. In
fact, it will not neccesarily take the shortest path even to another
machine in the same area. But that's another story. :-)
??? It certainly will, where "shortest" is defined as "least path
*cost*", not necessarily fewest hops.
paul
On 30.6.2010 15:45, Johnny Billquist wrote:
H Vlems wrote:
Johnny, the original DECnet manuals showed pictures of area routers that
were interconnected by WAN links. Each site had its own area number.
In fact
the name "area routing" implies clearly that the concept was meant to
set up
DECnet networks that were geographically separated.
Certainly. But that does not imply that just because you have physically
different locations that they must be in different areas. And areas
don't necessarily imply geography... :-)
Level 1 routers does exactly the same job, the same way, but keeps it
within one area.
But basically, the reasons for the different "levels" are originally
technical. You have segments, which more or less means directly
connected machines.
Then you have an area, which connects these segments. Traffic within a
segment can be fairly high. Between segments there is much less traffic,
since only traffic actually meant for a destination at the other end is
going through, and then of course the routing messages of the level 1
routers.
Level 1 routers knows where all machines in the same area are located,
and knows the most efficient way to any node within the same area.
However, it only keeps track of the closest area router, and knows
nothing about any other area.
Area routers work just like level 1 routers, but they also have an area
routing table, so they know the most efficient path to an area router
for any area.
So, an end node only knows what machines are on the same segment, and
which is the closest level 1 router. Level 1 routers knows where all
machines are in the same area, and knows where the closest area router is.
Area routers knows where every machine is on the local area, and also
where all area routers are.
Now, this means that a machine that sits in one area will not
neccesarily take the shortest path to a machine in another area. In
fact, it will not neccesarily take the shortest path even to another
machine in the same area. But that's another story. :-)
For most points and purposes, a level 1 router and an area router will
give you exactly the same effect.
So, just because you have machines that are physically remote is by no
mean a reason for them to be in separate areas. A level 1 router will
solve that just as well.
What areas bring to the table is essentially just that you expand the
address space, and add another level of hierarchy to the network. It is
(obviously) up to you how you want to interpret that extra level. I'm
not saying that you cannot use it to match network hierarchy to
geography, just that there is no technical reason to align things that way.
I ran a fairly large DECnet environment 20 years ago with >20
PDP-11's, >80
VAX systems >600 pc's and several alpha's, plus a few unix systems
that ran
DECnet too (in those days DECnet was the multiplatform protocol of
choice).
I seprataed each factory in its own DECnet area. DEC Holland got midly
interested in the design because they wondered whether the level 2
routing
overhead wouldn't hurt network performance. Which it didn't :-)
Can't see why it should. If you have a fairly busy network, the overhead
of the level 2 routing packets is very low. And if the network is mostly
idle, you have the capacity to spare anyway.
I'm surprised if DEC Holland was that curious, or didn't know better,
since DEC's internal network was way larger at that time.
They had already passed 60.000 nodes on Easynet (which was the name of
the internal network). I worked at DEC for a while in the 80s, and
Easynet worked just fine, and was very nice.
If I remember right, areas were sortof allocated by country, although
some places (like the US) used several, while some places shared one
between several countries.
Quite correct. Finland used area 50.
In early 1990's the Easynet had Phase V area routers, which also were used for TCP/IP routing (Integrated IS-IS).
Kari
One reason for separating systems in different areas was that
rebooting the
pc's would generate so many DECnet state up and down messages that
PDP-11's
and the older VAX systems choked in their console output.
Yeah, that can be an annoyance. But that's what the logging filters are
there for.
Johnny
Hans
-----Oorspronkelijk bericht-----
Van: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] Namens
Johnny Billquist
Verzonden: maandag, juni 2010 21:11
Aan: hecnet at Update.UU.SE
Onderwerp: Re: [HECnet] Attaching to hecnet
Brian Hechinger wrote:
Ok, so I should be getting to my plans soon enough here and had some
questions
about how I should set this up.
I'm going to install SIMH on the machine in colo (100mbit connection
here
in
the US, so might be useful as a "hub") as well as a small handful of
boxes
here at home.
Sounds good.
Should I just use one area? What's the best way to set that up?
Areas in DECnet are not really meant to be associated with physical
location, but rather with organizational. So keep it within one area.
For physically different locations, you might want to use level 1
routers, though. But as the internet nowadays is so fast, using just a
bridge, and pretend that it's all one ethernet segment also works just
fine.
Johnny
Geen virus gevonden in het binnenkomende-bericht.
Gecontroleerd door AVG - www.avg.com Versie: 9.0.830 / Virusdatabase:
271.1.1/2969 - datum van uitgifte: 06/28/10
20:35:00
.
H Vlems wrote:
Johnny, the original DECnet manuals showed pictures of area routers that
were interconnected by WAN links. Each site had its own area number. In fact
the name "area routing" implies clearly that the concept was meant to set up
DECnet networks that were geographically separated.
Certainly. But that does not imply that just because you have physically different locations that they must be in different areas. And areas don't necessarily imply geography... :-)
Level 1 routers does exactly the same job, the same way, but keeps it within one area.
But basically, the reasons for the different "levels" are originally technical. You have segments, which more or less means directly connected machines.
Then you have an area, which connects these segments. Traffic within a segment can be fairly high. Between segments there is much less traffic, since only traffic actually meant for a destination at the other end is going through, and then of course the routing messages of the level 1 routers.
Level 1 routers knows where all machines in the same area are located, and knows the most efficient way to any node within the same area. However, it only keeps track of the closest area router, and knows nothing about any other area.
Area routers work just like level 1 routers, but they also have an area routing table, so they know the most efficient path to an area router for any area.
So, an end node only knows what machines are on the same segment, and which is the closest level 1 router. Level 1 routers knows where all machines are in the same area, and knows where the closest area router is.
Area routers knows where every machine is on the local area, and also where all area routers are.
Now, this means that a machine that sits in one area will not neccesarily take the shortest path to a machine in another area. In fact, it will not neccesarily take the shortest path even to another machine in the same area. But that's another story. :-)
For most points and purposes, a level 1 router and an area router will give you exactly the same effect.
So, just because you have machines that are physically remote is by no mean a reason for them to be in separate areas. A level 1 router will solve that just as well.
What areas bring to the table is essentially just that you expand the address space, and add another level of hierarchy to the network. It is (obviously) up to you how you want to interpret that extra level. I'm not saying that you cannot use it to match network hierarchy to geography, just that there is no technical reason to align things that way.
I ran a fairly large DECnet environment 20 years ago with >20 PDP-11's, >80
VAX systems >600 pc's and several alpha's, plus a few unix systems that ran
DECnet too (in those days DECnet was the multiplatform protocol of choice).
I seprataed each factory in its own DECnet area. DEC Holland got midly
interested in the design because they wondered whether the level 2 routing
overhead wouldn't hurt network performance. Which it didn't :-)
Can't see why it should. If you have a fairly busy network, the overhead of the level 2 routing packets is very low. And if the network is mostly idle, you have the capacity to spare anyway.
I'm surprised if DEC Holland was that curious, or didn't know better, since DEC's internal network was way larger at that time.
They had already passed 60.000 nodes on Easynet (which was the name of the internal network). I worked at DEC for a while in the 80s, and Easynet worked just fine, and was very nice.
If I remember right, areas were sortof allocated by country, although some places (like the US) used several, while some places shared one between several countries.
One reason for separating systems in different areas was that rebooting the
pc's would generate so many DECnet state up and down messages that PDP-11's
and the older VAX systems choked in their console output.
Yeah, that can be an annoyance. But that's what the logging filters are there for.
Johnny
Hans
-----Oorspronkelijk bericht-----
Van: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] Namens
Johnny Billquist
Verzonden: maandag, juni 2010 21:11
Aan: hecnet at Update.UU.SE
Onderwerp: Re: [HECnet] Attaching to hecnet
Brian Hechinger wrote:
Ok, so I should be getting to my plans soon enough here and had some
questions
about how I should set this up.
I'm going to install SIMH on the machine in colo (100mbit connection here
in
the US, so might be useful as a "hub") as well as a small handful of boxes
here at home.
Sounds good.
Should I just use one area? What's the best way to set that up?
Areas in DECnet are not really meant to be associated with physical location, but rather with organizational. So keep it within one area.
For physically different locations, you might want to use level 1 routers, though. But as the internet nowadays is so fast, using just a bridge, and pretend that it's all one ethernet segment also works just fine.
Johnny
Geen virus gevonden in het binnenkomende-bericht.
Gecontroleerd door AVG - www.avg.com Versie: 9.0.830 / Virusdatabase: 271.1.1/2969 - datum van uitgifte: 06/28/10
20:35:00
Hi, Hans.
H Vlems wrote:
OK Johnny, talk to me :-)
This is my plan: I intend to modify two systems to try the connection to
HECnet.
1) I have a linux system under Fedora 9 that will run the bridge software
and an Alpha Server 1200 under VMS V8.3 and DECnet phase IV, address 1.1010.
That should work without any strange problems. You'll probably want to connect the bridge to me in that case. Let me know when you are ready to try.
2) a VAXstation 4000 model 90A, running VMS V7.3 and DECnet phase V, in area
44.
I'd like to try that connection without the linux system.
You need to find someone who can act as the other end in this case. Which I suspect meaning someone running phase V and as an area router. I don't know who might be doing this. Maybe someone who do can speak up.
Anyone know if this would be compatible with DECnet over IP as Multinet does it?
Option 2 is my preferred situation since it removes a by and large unknown
factor from the equation (the linux box).
Sure. We just need to identify someone you can connect to.
So, what do I need to know and to do to make this work?
Someone to connect to...
Johnny
Hans
-----Oorspronkelijk bericht-----
Van: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] Namens
Johnny Billquist
Verzonden: maandag, juni 2010 21:03
Aan: hecnet at Update.UU.SE
Onderwerp: Re: [HECnet] Attaching to hecnet
H Vlems wrote:
What I meant with the phase III-IV-V answer is that direct connectivity
between a phase V and phase III system won't work. But poor man's routing
will work with a phase IV node in between. Functionality of course is
limited by the phase III host :-)
I wonder if phase III to phase V neccesarily will not work. However, DEC never guaranteed that it will work, nor did they ever try it.
But you're absolutely right that very few people will have a phase III
system, RT-11 being the most likely candidate?
Probably. Or if someone is running some old versions of other systems.
I've seen the bridge program, but am not sure how to make the .conf file
work. Is it possible to use DECnet address 1.1010 to try and make this
work?
Yes. 1.1010 is not used by anyone, so that node number would be ok to use to test.
But you also need to talk with me (or someone else) with the bridge running, to act as the remote end.
Johnny
Hans
-----Oorspronkelijk bericht-----
Van: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] Namens
Johnny Billquist
Verzonden: maandag, juni 2010 11:02
Aan: hecnet at Update.UU.SE
Onderwerp: Re: [HECnet] Attaching to hecnet
Hi.
H Vlems wrote:
DECnet phase IV nodes are backwards compatible with phase III.
Yes. But the question here was if phase V will interoperate with phase III. I don't know the answer to that one, but on the other hand, I don't think anyone around is running phase III anyway.
There are no restrictions in functionality between phase IV nodes and
phase
V as seen by the unpriviledged user. Area routing may be an issue on
Alpha,
and of course ncl is more of a pain to remember than ncp ;-)
True, as far as that goes.
However, I am not sure that a phase V node can operate as a phase IV area router.
Someone else pointed out that although DEC claimed that alphas could not be area routers, that information is incorrect, and you can just tell an Alpha VMS phase IV node to be an area router, if you want to.
However, DECnet+ is phase V, and all bets are off. :-)
And yes, not only are the NCL commands more difficult to remember (atleast for me), the node name management is way more difficult as well. Do anyone know how you copy a nodename database from another machine with DECnet+?
Two questions:
1-May I use area 44?
Sure.
2-Is there a short guide to set up DECnet over IP to connect to HECnet?
Not that I know of. Maybe Mark Wickens have something on hecnet.eu?
My page (http://www.update.uu.se/~bqt/hecnet.html) only have information about the bridge.
Johnny
Hans
-----Oorspronkelijk bericht-----
Van: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] Namens
Marc Chametzky
Verzonden: maandag, juni 2010 0:04
Aan: hecnet at Update.UU.SE
Onderwerp: Re: [HECnet] Attaching to hecnet
DECnet-Plus isn't
able to connect, or at least reliably connect to all OS's that can
potentially be on HECnet. I forget what all OS's I was having issues
with, I know one was RSTS/E v10.1, but I want to say it also included
VAX/VMS. Once I *upgraded* my Alpha running OpenVMS to DECnet Phase IV,
all these issues went away. These were things as simple as SET HOST.
It's probably that DECnet-Plus (Phase V) cannot speak with DECnet Phase III (such as on RSTS/E and TOPS-10/20). That's my guess anyway.
Phase V should be able to communicate with VAX/VMS since that's Phase IV, which is the gold standard of DECnet, IMHO.
--Marc
Geen virus gevonden in het binnenkomende-bericht.
Gecontroleerd door AVG - www.avg.com Versie: 9.0.830 / Virusdatabase: 271.1.1/2966 - datum van uitgifte:
06/27/10
08:35:00
Geen virus gevonden in het binnenkomende-bericht.
Gecontroleerd door AVG - www.avg.com Versie: 9.0.830 / Virusdatabase: 271.1.1/2968 - datum van uitgifte:
06/28/10
08:37:00
Geen virus gevonden in het binnenkomende-bericht.
Gecontroleerd door AVG - www.avg.com Versie: 9.0.830 / Virusdatabase: 271.1.1/2969 - datum van uitgifte: 06/28/10
20:35:00
I would like to claim area 52.
-brian
--
"Coding in C is like sending a 3 year old to do groceries. You gotta
tell them exactly what you want or you'll end up with a cupboard full of
pop tarts and pancake mix." -- IRC User (http://www.bash.org/?841435)
Paul,
The overhead incurred by level 1 or level 2 routing was pretty low. The site
I mentioned in the earlier example grew to more than 1000 pc's. They all ran
DECnet for Pathworks connectivity. They just fitted in one DECnet area. The
area routing was performed by two microVAX II systems, one active, the other
backup. They did nothing but area routing and had sufficient cpu power and
memory available. Ethernet was 10BASE2 in those days and that worked well.
The only traffic outside the area was CTERM and a little FAL.
The reason we didn't turn of console logging was that plant personnel
archived the console logs for reference purposes.
Hans
-----Oorspronkelijk bericht-----
Van: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] Namens
Paul Koning
Verzonden: dinsdag, juni 2010 12:55
Aan: hecnet at Update.UU.SE
Onderwerp: RE: [HECnet] Attaching to hecnet
Johnny, the original DECnet manuals showed pictures of area routers
that
were interconnected by WAN links. Each site had its own area number.
In
fact
the name "area routing" implies clearly that the concept was meant to
set up
DECnet networks that were geographically separated.
I don't remember those pictures, but this is an issue that generated a
lot of debate and a lot of annoyance in the DECnet architecture group.
...
One reason for separating systems in different areas was that
rebooting
the
pc's would generate so many DECnet state up and down messages that
PDP-
11's
and the older VAX systems choked in their console output.
That's a good one. (Actually, the way to deal with that is to turn the
logging to console off for that event...) Yes, that's a valid example.
The purpose of area routing is to avoid having things get too large.
There were various opinions on how big an area (or Phase III network)
could reasonably be. Originally the limit was assumed to be about 32,
without any basis that I know of. That too produced a pile of debate,
and later on it became obvious you could go much higher. But clearly
you couldn't run a flat Phase III style network with 10,000 nodes.
For that reason area routing was introduced, so each instance of the
routing algorithm (in-area and level 2) would deal with a reasonably
small topology. Again debates broke out whether a full area (1000
nodes) was acceptable. It turned out yes, but certainly keeping it
smaller, say to 100-200, would be a good thing if possible.
Geography isn't a consideration unless the links are slow enough to make
route change propagation an issue. Corporate organization (different
departments) CERTAINLY isnt' a consideration, though some people tried
to argue that it was valid to do so.
paul
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