Subject: Re: AD comments on draft-ietf-ipv6-router-selection-02.txt

From: Robert Elz <[email-masked]>
Date: Thu, 01 Aug 2002 18:01:52 +0700

Date:        Wed, 31 Jul 2002 14:36:15 -0700
    From:        Bob Hinden <[email-masked]>
    Message-ID:  <[email-masked]>

  | Sorry, I wasn't clear.  Keep the load-sharing that applies to routers of 
  | equal priority in the router-selection draft.  Load-sharing should be done 
  | in these cases.  The text that applies to the basic ND default-router case 
  | should be removed as it would duplicate the load-sharing draft.

I'm still not clear what this means.   I really think that one doc for
both of these is what is desirable.

I suspect that part of the problem is that the relationship (or at least
what I would like the relationship to be) isn't clear.

That is, if load sharing is done, router preferences MUST be done as well.

So, whatever status we give to load sharing, router preferences has to have
at least the same status.   I'm not sure that got adequately represented in
the draft.

The reason is that it simply isn't acceptable for nodes to start broadcasting
packets over all routers on the link at random.   If we don't have load 
balancing, it is possible to arrange for the "right" routers to get used
(though in situations where load balancing would help, the net loses).

If we have some kind of mandatory load balancing however, there needs to
be a way for the net administrator to control it, and router prefs are
that way - we can load balance amongst the preferred routers, and just
ignore the others we're not going to choose anyway.

Splitting this back into 2 docs will, I suspect, revert to the situation
we had before, where "everyone has to implement load balancing" (because if
they don't, it is useless), but router prefs are optional (because people
keep wondering if it is possible to configure them properly, which is
bizarre, but never mind).

Keep it as one, but get the requirements right.

kre

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From: Markku Savela <[email-masked]>
Date: Thu, 1 Aug 2002 14:59:34 +0300

> X-Authentication-Warning: sunroof.eng.sun.com: majordomo set sender to [email-masked] using -f

>   | should be removed as it would duplicate the load-sharing draft.

If we have two routes

   prefix1/K -> router1
   prefix2/L -> router2

with K < L, and such that prefix1/K == prefix2/K (e.g. shorter prefix
also covers addresses of the longer prefix).

- which is more significant priority or prefix length?

- if router2 is not reachable, obviously packets matching prefix2/L
  can be sent to router1. But, is there any advice on algorithm how
  the system detects if router2 becomes available? Just wait for RA?
  Probe with some logic?. (There is no RA in IPv4 -- I think this
  should work for IPv4 too!)

Note: default routes are just a special case where K=0

---

From: Robert Elz <[email-masked]>
Date: Thu, 01 Aug 2002 20:40:14 +0700

Date:        Thu, 1 Aug 2002 14:59:34 +0300
    From:        Markku Savela <[email-masked]>
    Message-ID:  <[email-masked]>

  | - which is more significant priority or prefix length?

prefix length.   The draft is quite clear about that.   The preferences
are only a method to allow routers that would otherwise be considered
equal to be ranked (a last step disambiguator).

kre

---

From: Markku Savela <[email-masked]>
Date: Thu, 1 Aug 2002 17:56:41 +0300

> From: Robert Elz <[email-masked]>

Ok, that much I sort of guessed, but is there as simple answer to my
followup question:

Ok, so my address matches the route for router2, but this router is
currently unreachable (no entry in neighbor cache). Do I 

a) drop the packet

b) if there is a reachable router with shorter matching prefix, send
   there

I guess (b), but then the question is when and how is router2
"rediscovered". I'm pretty sure I can invent some ad hoc algorithm,
but I also wanted to know other opinions?

---

From: Robert Elz <[email-masked]>
Date: Thu, 01 Aug 2002 22:01:35 +0700

Date:        Thu, 1 Aug 2002 17:56:41 +0300
    From:        Markku Savela <[email-masked]>
    Message-ID:  <[email-masked]>

  | I guess (b), but then the question is when and how is router2
  | "rediscovered". I'm pretty sure I can invent some ad hoc algorithm,
  | but I also wanted to know other opinions?

See section 3.4

kre

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From: Erik Nordmark <[email-masked]>
Date: Thu, 1 Aug 2002 19:37:40 +0200 (CEST)

> at least the same status.   I'm not sure that got adequately represented in

Given that load sharing is currently described as mandatory, your point
implies that router preferences should also be mandatory.

Perhaps others have different views. Given the 3 pieces 
	load sharing,
	router preference, 
	more specific routes (which have preference a load sharing themselves)

we might have the following choices (I can't think of other combinations that
make sense to me):
1. all are optional
2. load sharing is mandatory; others are optional
3. load sharing and router preferences are mandatory; more specific is optional
4. all are mandatory

The current document says #2. Your point is #3 as far as I can tell.
I guess the WG needs to choose.

But independent of this, if is confusing to have both mandatory and optional
protocol pieces in the same document if it can be easily avoided.

  Erik

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From: Bob Hinden <[email-masked]>
Date: Fri, 02 Aug 2002 15:16:11 -0700

>3. load sharing and router preferences are mandatory; more specific is 

The current proposal is to split the document and make load sharing 
mandatory and router preferences and more specific routes optional.  This 
is choice 2.

As far as I can tell only one person has objected to this approach and has 
suggested choice 3. (perhaps 4).

Are there any other objections to the current proposal?

Bob

p.s.

>protocol pieces in the same document if it can be easily avoided.

Me too.

---

From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Sat, 17 Aug 2002 17:19:19 +0900

>>>>> On Fri, 02 Aug 2002 15:16:11 -0700, 
>>>>> Bob Hinden <[email-masked]> said:

> Are there any other objections to the current proposal?

If the load sharing is mandated unconditionally, I think I would make
an objection (I guess I'm not the "only one person"...).  I believe we
discussed this before and reached a consensus on this, so I won't
repeat my points (for now).

Perhaps the problem is in wording.  My understanding of the MUST is
"if a node implements (some parts of) the draft (which is optional),
it MUST support the load-sharing algorithm".  I don't see any
contradiction here.

However, I don't actually care about the 1 or 2 documents issue, as
long as the fact that load-sharing applies to some limited (but
reasonable) environments is clear.

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					[email-masked]
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From: Robert Elz <[email-masked]>
Date: Sat, 17 Aug 2002 18:06:56 +0700

Date:        Sat, 17 Aug 2002 17:19:19 +0900
    From:        JINMEI Tatuya / =?ISO-2022-JP?B?GyRCP0BMQEMjOkgbKEI=?=
		 <[email-masked]>
    Message-ID:  <[email-masked]>

  | If the load sharing is mandated unconditionally, I think I would make
  | an objection (I guess I'm not the "only one person"...).

No, I think that meant me ...

  | I believe we
  | discussed this before and reached a consensus on this, so I won't
  | repeat my points (for now).

I thought we had too, which is why the two docs had become one.

  | Perhaps the problem is in wording.  My understanding of the MUST is
  | "if a node implements (some parts of) the draft (which is optional),
  | it MUST support the load-sharing algorithm".  I don't see any
  | contradiction here.

If that's the interpretation, then I also have no problems.   However,
that's not the impression that has been given (over and over again).
The impression I keep getting is that load sharing is to be mandatory
(in the sense of must be implemented).   And there's no knob anywhere
(other than perhaps visiting every node individually) to allow a net
manager to disable it - or not without router prefs.   Which is why
I want router prefs to have no lesser status than load balancing.

kre