Subject: [mobile-ip] Mobile IPv6 Issue 154: ND Constants (Router Advertisement)

From: Greg Daley <[email-masked]>
Date: Thu, 05 Dec 2002 12:14:50 +1100

(sorry the email is so long).
I'm interested in reaching a consensus and getting text
for this issue.

There seems to be two sets of constants:

RA Multicast Advertisement Intervals.
(MinRtrAdvInterval, MaxRtrAdvInterval).

RS Retransmission constants.
    (Delaying 0 to MAX_RTR_SOLICITATION_DELAY
             before sending RS)
    Retransmitting RS's more often than is
             mandated in RFC2461

To date most of the discussion has been on RA intervals,
but also there's some need for agreement on RS constants
in the MIPv6 draft.

the discussion summary is here:
http://www.piuha.net/~jarkko/publications/mipv6/issues/issue154.txt

I'll be sending out two emails, tackling each message [RA|RS]
separately.

(jari: do we need a separate issue for RS?)

Here's a list of the RA interval issues as I see it:

* MIPv6 needs better movement detection than RFC2461 allows.

* there is only one L3 (no triggers, layer violations)
    mechanism proposed which allows faster movement detection
    -> Reducing the interval between Multicast RA beacons
        (increasing number per second).

* some believe that reducing the interval to 50 ms
   (mean 20 RA/sec) will provide adequate response for
   many transports/applications  (some experimental experience?)

* There is some strong concern that some link layers/environments
   will be affected by this rate of multicast packets on the
   wireless interface.

* Other solutions are considered to provide better movement
   detection performance, without the rapid transmission
   overhead.

* Most people preferred to put the RA advertisement interval
   constant changes in MIPv6, and chance IETF last call.

* There was some confusion as to what the effect of the current
   constant values were achieving.

* There is some concern that certain link layers will spread out
   multicast RA's when there is cell contention.

* there is also some lack of consistency between section 12
    (Protocol Constants) and section 7.5 (Changes to Sending
    Router Advertisement) which should be addressed.

As a way to go forward, I propose that we modify section 7.5 and
section 12 in the following manner:

(section 7.5)
* Specify new lower bounds for the advertisement interval
   constants, making explicit that these are the lowest values
   currently required in MIPv6 (to simplify the task of implementors).
   (2-3 lines??)

* Explain the mean interval generated by using the low bound constants
   (1 line ??)

* Provide an applicability statement, ensuring that these values
   are not configured by default, and that deployers check that
   the interval is necessary, and not harmful in their environment.
   (2-3 lines??)

* Keep current information about Link triggers, to indicate
    an alternative to short multicast intervals.

* Specify a safety boundary/grace time for handling of the
    "Advertisement Interval" option in RA's, to make sure
    that scheduling/link jitter doesn't cause excessive
    Router Solicitations at the short intervals we're currently
    discussing.
    (3-4 lines??)

(Section 12)

* Specify all modified RA protocol constants (in list, and
   references to rfc 2461).

As another action, I'm sure that some people are interested in
continuing work on Movement detection optimization techniques.
Based on the consensus at the meeting, these will be tackled in
other document(s).  This is similarly the case with dynamic
interfaces.

Some of these concepts may be re-linked in through Informational
and BCP documents in the future..

What do people think about this?

Is there anything which looks incorrect or needs addition?

Greg Daley

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From: "James Kempf" <[email-masked]>
Date: Wed, 4 Dec 2002 18:45:50 -0800

There was discussion at the WG meeting about moving all ND changes but the RA
advertisement interval and behavior upon detecting a collision during DAD to a
separate draft.

Is there concensus now about making all ND changes in the base draft?

Personally, I'd like to see those changes to ND which people don't feel are
absolutely necessary (i.e. everything but the RA advertisement interval and DAD
collision behavior) deferred to a new draft. This will give us more time to
consider a proper design.

            jak

---

From: Greg Daley <[email-masked]>
Date: Thu, 05 Dec 2002 14:39:34 +1100

Hi James,

I've just sent the other email.

There's no consensus to make all ND changes in the base
draft.  The main reason is to identify all the areas
covered by the AD comments on ND and cover them.

Issue 154 still had some reference to RS, which was
not yet addressed in any other issue.  There are
also some minor modifications to ND timers in MIPv6-19,
which seem to be innocuous and limited in scope,
as well as those in section 7.5/7.6.

The main idea was to get the RA intervals specified
and determine what to do with the RS stuff.
Maybe the RS specific comments can be directed to the
other thread, so that we can concentrate on getting
to an agreement on the requirements for RA interval,
in this one.

Greg

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From: Vijay Devarapalli <[email-masked]>
Date: Thu, 05 Dec 2002 19:24:22 -0800

> What do people think about this?

It looks good. I think this is quite enough.

Vijay

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From: "JinHyeock Choi" <[email-masked]>
Date: Fri, 6 Dec 2002 22:10:17 +0900

>     an alternative to short multicast intervals.

It's better to ensure that these are not default values and 
deployers can use alternative methods if they want to.  

> and BCP documents in the future..

Those kinds of documents will be useful for actual deployment.  
 
> What do people think about this?

I think this is a sensible proposal.

---

From: "JinHyeock Choi" <[email-masked]>
Date: Fri, 6 Dec 2002 22:13:22 +0900

> consider a proper design.

I agree. It will speed up the process of base draft.  

Jin