Subject: [mobile-ip] MN processing of Home Agent Address Discovery Reply message

From: "Ed Remmell" <[email-masked]>
Date: Mon, 18 Nov 2002 16:23:47 -0700

Hello,

I'm currently doing an embedded systems implementation of draft 19 of Mobile
IPv6, host (CN and MN) only.

The latest draft of Mobile IPv6 has the following requirement regarding MN
processing of the Home Agent Address Discovery Reply message:
	"If the home agent identified by the Source Address field in the IP header
of the packet carrying the Home Agent Address Discovery Reply message is not
listed in the Home Agent Addresses field in the Reply, it SHOULD be tried
before the first address given in the list; otherwise, it SHOULD be tried in
its listed order."

This SHOULD requirement means that every time we process a Home Agent
Address Discovery Reply message (which, admittedly isn't that frequent, but
still it's the principle here that counts), we need to first check the list
of Home Agent entries in the message looking for a match on the source
address of the message, which potentially means we need to search the entire
list. If we don't find the source address in the list, then we try to use it
as our Home Agent, otherwise we did find it in the list (yippee!) which cuts
our search short and allows us then to pick the first Home Agent in the
list. I think this was designed to account for the fact that all of the Home
Agent entries in the list need to fit within the MTU, and then potentially
eek'ing out room for just one more Home Agent entry (i.e. the sender of the
message). Come on. Just how many Home Agent addresses do you need to put in
the list? Even (especially) if the list fills up the entire MTU, I should
not have to search through the entire (or even most of the) Home Agent list
to be able to select a Home Agent to send to. That is pretty wasteful of the
limited CPU cycles (and battery power) that many embedded systems have.

I suggest that you require the HA address to be in the list always, i.e. no
exception for the MN to try the source IPv6 address of the Home Agent
Address Discovery Reply message first if it doesn't appear in the list.

Thanks.
- Ed Remmell
Elmic Systems, USA
http://www.elmic.com

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From: "Kevin Miles" <[email-masked]>
Date: Wed, 20 Nov 2002 13:33:41 -0000

Ed,

This 'optimisation' was previously considered as Issue #56 and current text reflects the resolution.

FWIW, I agree with you that the bits saved are not worth the effort at HA and MN.

Kevin.
> -----Original Message-----
> From: [email-masked]
> [mailto:[email-masked]]On Behalf Of Ed Remmell
> Sent: 18 November 2002 23:24
> To: Mobile IPv6 mailling list
> Subject: [mobile-ip] MN processing of Home Agent Address 
> Discovery Reply
> message
> 
> 
> Hello,
>

---

From: Jari Arkko <[email-masked]>
Date: Mon, 25 Nov 2002 17:19:27 +0200

> Address Discovery Reply message first if it doesn't appear in the list.

Like Kevin, I too agree that this is a rather unnecessary optimization.
But we *did* discuss this earlier and I don't want to re-open old
issues unless there's a real problem. My proposal is that we stick to
the results of the old discussion.

Jari

---

From: "Ed Remmell" <[email-masked]>
Date: Mon, 25 Nov 2002 09:37:26 -0700

Jari -

Fortunately, DHAAD doesn't occur very frequently ;-)

OK, go ahead and close this one with no action required.

Thanks.
- Ed

> [mailto:[email-masked]]On Behalf Of Jari Arkko
> Sent: Monday, November 25, 2002 8:19 AM
> To: Ed Remmell
> Cc: Mobile IPv6 mailling list
> Subject: Re: [mobile-ip] MN processing of Home Agent Address Discovery
> Reply message
> 
> 
> Ed Remmell wrote:
>