Subject: [mobile-ip] please clarify that MN can do DHAAD on home network

From: "Ed Remmell" <[email-masked]>
Date: Mon, 18 Nov 2002 16:33:23 -0700

Hello,

I appreciate the fact that the latest draft 19 removes the requirement that
the MN must maintain a Home Agent list; DHAAD is a fine solution in itself,
there is no need to be redundant (especially since in an embedded systems
implementation, this redundancy results in extra code/ROM usage which I'm
trying to avoid). However, I didn't see explicit clarification in draft 19
that the MN can use DHAAD when attached to its home network (as well as when
attached to a foreign network) to discover the addresses of its home agents,
you would assume from the way that the protocol is defined that this should
be a no-brainer but it might be nice to have some clarification to that
extent to avoid broken HA implementations that don't let a MN do DHAAD while
at home. In fact, I found the opposite in draft 19 (hopefully a relic from
previous versions), i.e. a requirement that prohibits the MN from doing
DHAAD on its home network:

Section 6.5 "ICMP Home Agent Address Discovery Request Message" says:
"The Source Address of the Home Agent Address Discovery Request message
packet MUST be one of the mobile node's current care-of addresses."

When the MN is at home, it doesn't have a CoA, so this appears to prohibit
the MN from doing DHAAD while at home. Please remove this restriction to
allow the MN to do DHAAD while at home, and add additional clarification
that the MN can do DHAAD either while attached to its home network or while
attached to a foreign network.

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

---

From: Jari Arkko <[email-masked]>
Date: Sun, 24 Nov 2002 19:55:24 +0200

> attached to a foreign network.

Given that the MUST in 6.5 is pretty clearly untestable (how would
you know if this is the mobile's coa if it didn't register yet?), I'm
willing to soften the language in 6.5 to the following:

    The Source Address of the Home Agent Address Discovery Request
    message packet is typically one of the mobile node's current care-of
    addresses. At the time of performing this dynamic home agent address
    discovery procedure, it is likely that the mobile node is not
    registered with any home agent. Therefore, neither the nature of
    the address nor the identity of the mobile node can be established
    at this time. The home agent MUST then return the Home Agent Address
    Discovery Reply message directly to the Source Address chosen by the
    mobile node.

However, I'm not sure I specifically want to go out and say that
DHAADs should be used, since it appears that IPv6 RAs are sufficient
as well. Since you are an IPv6 host you apparently must spend your ROM
for this anyway. (Yes, when you track HAs you must look at a few additional
bits.)

Jari

---

From: "Ed Remmell" <[email-masked]>
Date: Mon, 25 Nov 2002 07:49:26 -0700

Jari -

Your proposed text change is fine. Thanks.

Actually, since we can use DHAAD when at home, our MIPv6 MN implementation
will not be paying attention to the additional HA-specific information in
the RAs, instead we will continue processing RAs per the normal ND rules.
This will allow us to reduce code size and complexity a little, but every
little bit helps.

It seems reasonable for the MN to attempt to use DHAAD while at home (i.e.
before moving) to attempt to find a usable HA before starting movement to a
foreign network, that reduces move latency.

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

> -----Original Message-----
> From: Jari Arkko [mailto:[email-masked]]
> Sent: Sunday, November 24, 2002 10:55 AM
> To: Ed Remmell
> Cc: Mobile IPv6 mailling list
> Subject: Re: [mobile-ip] please clarify that MN can do DHAAD on home
> network
>
>
> Ed Remmell wrote:
>