Subject: RE: ND-proxy applicability and loop-prevention

From: "Soliman Hesham" <[email-masked]>
Date: Tue, 23 Mar 2004 02:30:15 -0500

Pekka, 

I think you're oversimplifying the following issue:

 > > It *might* be sufficient if the solution could detect 
 > loops and sound the alarm
 > > (and stop forwarding frames), but ndproxy can't even 
 > detect loops and shut
 > > itself off. Thus when loops are formed the result is that 
 > the consumer will
 > > see their network die (100% link utilization due to frames 
 > looping around
 > > forever; ndproxy doesn't decrement the hop count).
 > 
 > I don't personally think 100% link utilization is that bad a 
 > signal.  

=> I think it's a bad signal, _if_ detected. I.e. An average
user is not even going to know that they have 100% link
utilisation. And _if_ they do, I actually think that neither
the user, nor the help desk first line of support will
have the faintest idea (having been a regular with help
desk people that work for a couple of major operators
in different countries).

 > It rather simply conveys that "oops-- I've done something 
 > wrong when I
 > added the box there." and after it's removed all starts to work again
 > -- intuitive.  

=> So if I somehow get inspired or guess that I should 
remove the proxy and things work, what does that tell me???
Maybe the device is faulty? Maybe I'll take it back to the 
shop! There is nothing intuitive about that from an average
user's perspective. 

Hesham

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From: Pekka Savola <[email-masked]>
Date: Tue, 23 Mar 2004 13:07:58 +0200 (EET)

> desk people that work for a couple of major operators

The user knows that all of his communication attempts fail.  That's a 
good signal that there's something wrong.  If the user knows nothing 
more of this, he calls helpdesk or some support, which may be able to 
identify the problem and eliminate it.

Or, the user could read the manual for the shiny box he bough, and
notice a big warning text "DON'T LINK THESE BOXES EXCEPT IN SERIES
UNLESS YOU DISABLE ND-PROXYING [and instructions how to do it]"

> shop!

Maybe the shop knows something about how the device operates -- they 
certainly should! -- or you read documentation, which should certainly 
describe this feature.

All in all, it seems that the problem gets noticed and fixed by 
someone and that's what counts.

> There is nothing intuitive about that from an average
> user's perspective. 

For the average user, it doesn't have to be more intuitive than that,
right?  He only cares whether it works or not.  In the first place
99.9% of people wouldn't be plugging these boxes in triangles (or more
complex setups), so this is not commonplace.  If the box "doesn't
work", he complains to someone, and that someone may be able to help.

In the end, the problem gets fixed in one way or the other (probably 
removing the unnecessary box, replacing it with another router, or 
putting the boxes in series, or whatever), and the user who happened 
to add them in the wrong configuration is happy again.

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

---

From: Erik Nordmark <[email-masked]>
Date: Wed, 24 Mar 2004 14:06:54 -0800 (PST)

> identify the problem and eliminate it.

Which help desk should my grandmother call when this happens?
The ISP? The vendor for her Tivo-like box? The OS vendor for the laptop?

I think what we want is the complexity equivalent of plugging together
electrical extension cords. Looking at Ethernet we don't have the male/female
distinction on the plugs hence it is a lot easier to create Ethernet loops than
power extension cord loops. Combining this with wireless makes it even more
likely that there will be accidental loops.

> work", he complains to someone, and that someone may be able to help.

Given that we don't even know what such boxes will look like in 10+ years,
how can we determine that people would not "plug" them together?
Perhaps this ability to connect multiple wired and wireless media
will be to cheap that every laptop, TV and stereo will include it.
(Many things that don't run on batteries might have such functionality
for all I can predict.)

   Erik

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From: Pekka Savola <[email-masked]>
Date: Thu, 25 Mar 2004 08:18:27 +0200 (EET)

> The ISP? The vendor for her Tivo-like box? The OS vendor for the laptop?

The same helpdesk she calls when she encounters a weird problem in her 
network connectivity, or in her PC.  Most likely you ;-)

(This is a much more generic problem, not one specific to this 
scenario, obviously.)

> (Many things that don't run on batteries might have such functionality

You are making assumption that those boxes would also be acting as
routers (in the ND-proxy mode) by default, right?  I don't, and I
don't think doing that would make a lot of sense.

---

From: Erik Nordmark <[email-masked]>
Date: Thu, 25 Mar 2004 15:55:19 -0800 (PST)

> (This is a much more generic problem, not one specific to this 

But in this particular case you seem to be arguing that plug&pray
is sufficient while I argue that we should aim for plug&play;
I think the futuristic goal is that wiring together network devices
shouldn't be more complex than plugging in electrical appliances.

> don't think doing that would make a lot of sense.

No.
I'm only making the same assumption that underlies ndproxy as well as the 
zerouter discussion; there will be L2s that do not support IEEE 802 bridging.
If you disagree with this assumption we don't need ndproxy or zerouter
for the home networking case - IEEE 802 bridging has already solved the
problem.

Given that you have different types of L2s in common use in the home, a subset
of  of consumer electronics will connect to multiple types of L2s.
Question is what these boxes implement to make the home network plug&play.
I'm not assuming the solution will be at L3; there are L2.5 solutions
possible as well.

   Erik

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From: Pekka Savola <[email-masked]>
Date: Mon, 29 Mar 2004 15:24:10 +0300 (EEST)

Btw -- one aspect was mentioned by Mohan P. on v6ops list: whether the
ND-proxy could decrement TTL instead of keeping it the same.  I don't
think whether this would affect this discussion (i.e., whether such a
proxy would be considerably better in this respect) has been
considered.

> shouldn't be more complex than plugging in electrical appliances.

For the deployment I have in mind, plug&pray and plug&play are pretty 
much equivalent.  There are certainly other things, labeled plug&play 
which are much more brittle than this :)

> for the home networking case - IEEE 802 bridging has already solved the

OK -- maybe you're thinking of this in more generic terms, like, every 
VCR or equivalent having its own (more or less) internal media for 
which IP connectivity would be desirable.  And that such media would 
not be currently IEEE bridgeable. (And when you combine this to a 
scenario when such a "VCR++" has WLAN uplink to the other devices at 
home, you might end up in a mess.  With wired connectivity, you'd be 
OK.)

On the other hand, I have been looking at the scenario where an 
explicit set of "routers" (or a home PC or whatever) would be proxying 
for the nodes connecting to that box.

We certainly seem to have an indication that the latter is important.  
I do not have personal knowledge if the former would be.  It'd be 
interesting to know.

---

From: Brian Haberman <[email-masked]>
Date: Mon, 29 Mar 2004 08:32:37 -0500

Pekka,
      Maybe I missed it, but how can we decrement the Hop Count
for loop prevention when receiving nodes are using the Hop
Count=255 check on reception?

Regards,
Brian