Subject: (IPng 7240) Re: IPv6 mobility support

From: Charles Perkins <[email-masked]>
Date: Thu, 25 Feb 1999 07:19:16 -0800 (PST)

With Alex's permission, I forward the following:

------------- Begin Forwarded Message -------------

Date: Wed, 24 Feb 1999 09:28:22 -0800 (PST)
From: Charles Perkins <cperkins@hsmpka>
Subject: Re: IPv6 mobility support
To: "Alex A.M.R. Slingerland" <[email-masked]>

		.........

> 1. Section 10.5 of draft-ietf-mobileip-ipv6-0{67}.txt _suggests_ that a
> MN, after changing primary care of address, _must_ send the first/next
> BindingUpdate to its Home Agent (HA). Does the first paragraph of
> Section 10.5 just say that the MN must inform the HA of the care of
> address change, or that the MN must do so before informing any other
> nodes? Would it reduce packet loss if the MN could first tell the old
> Default Router of the new care of address (i.e. allow the MN to have
> it's own policy)?

This is a good point.  I would agree that the MN could send a
binding update to its old default router before sending the
binding update to the Home Agent.  This has never come up in the
discussion before, and so as far as I know no one thought about it.
 
> 2.  (Section 10.10) Is MAX_UPDATE_RATE intended to limit the total rate
> of Binding_Updates that leave a MN, or does it apply to the rate of
> Binding_Updates to individual nodes/IP-addresses?
> - If the former is the case (limit total rate), after sending the
> BindingUpdate to the HA, the MN has to wait Max_Update_Rate (=1) seconds
> before it can send another BindingUpdate, to any other node (e.g. its
> old Default Router)? 
> - If the latter is the case (limit rate to individual nodes), the more
> CN's a MN is communicating with, the higher the (aggregate) rate of
> Binding_Updates after a care-of-address-update, correct? Would this
> cause load spikes, even if the Binding_Updates are put in packets that
> are destined for the CN anyway (perhaps the common case, if the MN's
> communicating with a CN)?

A good solution would be to define two update rates.  The MAX_UPDATE_RATE
for a correspondent node could be 1 second.  I don't think it was ever
the intention to restrict the total update rate to one per second.
Indeed, I would even go further to say that the MAX_UPDATE_RATE should
only apply to _empty_ packets.  The update rate for Binding Update
options that are inserted into normal data traffic might well be
unrestricted, or perhaps instead restricted to a small percentage
of the overall data volume.

Regards,
Charlie P.

		.........

> 
> Thanks for you time, 
> Alex.
> --
>       ___o___ 
>   ___  | | |    Alex Slingerland        <[email-masked]>
>  /   \ | | |    University of Twente          Tel. +31 53 489 4099
> |      | | |    Centre for Telematics and Information Technology
>  \___/ | | |    P.O. Box 217   NL-7500 AE Enschede The Netherlands

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---

From: Dave Johnson <[email-masked]>
Date: Mon, 15 Mar 1999 22:01:24 -0500

>discussion before, and so as far as I know no one thought about it.

I don't remember this has been discussed before, but the design
I intended in writing the text was simply what it literally says.
That is, the mobile node MUST register the new care-of address in
order to make it its primary care-of address.  The primary
care-of address is the address of the mobile node as registered
at the home agent.  This is used to tunnel intercepted packets
from the home agent.  This says nothing (and is intended to say
nothing) about what the mobile nodes uses as the care-of address
it sends to correspondent nodes.  The paragraph in Section 10.5
only talks about registering the primary care-of address.  See the
definition of primary care-of address on page 8.

So, the specific answer to your question is, yes, the mobile node
can send a Binding Update to correspondent nodes before it sends
the Binding Update to its home agent.

>of the overall data volume.

The value MAX_UPDATE_RATE relates only to Binding Updates sent by some
node about a specific binding.  It is not a global value to be applied
to all Binding Updates sent by that node, since the need to send
updates about one binding has no logical relationship about the need
to send updates about a different binding.  So that means, for
different home addresses (if the mobile nodes has more than one), the
rate is limited saparately.  If the mobile node sends a different
care-of address, the rate is limited separately.  If the update is
going to a different destination, the rate is limited separately.
If you are worried about "load spikes", you can limit the rate
further, but that is not the point of MAX_UPDATE_RATE.  THe limit
here is intended to prevent you from saying the same thing to the
same person too frequently.  In looking back at the text in the draft
right now, I see that this isn't explained very clearly, though,
so thanks for asking.  I'll clarify the text.

					Dave

---

From: "Alex A.M.R. Slingerland" <[email-masked]>
Date: Wed, 17 Mar 1999 12:18:23 +0100

> so thanks for asking.  I'll clarify the text.

Thanks for the clarifications. 

The other part of my question was *whether it would reduce
packet loss* if the MN would first inform the previous
default router of the new CoA (note that section 10.8 says
the previous DR is informed *after* changing the primary
CoA). 

If "after changing primary CoA" means "after sending the
Binding Update to the HA", I deduce from the above that the
answer is "no" or "not much", as the MN could send a binding
update to the previous DR *immediately* after (as rate
limiting on binding updates is done on a per binding, per
destination basis) sending the binding update to the HA. You
say the MN can even do this before informing the HA of the
to-be-primary CoA.

Do I understand you correctly?

Regards, 
Alex.
--
      ___o___ 
  ___  | | |    Alex Slingerland       
<[email-masked]>
 /   \ | | |    University of Twente          Tel. +31 53
489 4099
|      | | |    Centre for Telematics and Information
Technology
 \___/ | | |    P.O. Box 217   NL-7500 AE Enschede The
Netherlands

---

From: "Alex A.M.R. Slingerland" <[email-masked]>
Date: Wed, 17 Mar 1999 12:18:23 +0100

Regards, 
Alex.