Subject: [mobile-ip] Resolution for issue #218 (reopening 198)

From: gabriel montenegro <[email-masked]>
Date: Wed, 19 Feb 2003 03:39:21 +0100

There's been a lot of discussion on this item (under the subject
of issue 198), both on and off the list (although it's all recorded
under the issue entry on Jari's site). Now that the discussion
has died off, I'd like to find what the small set of agreements
is to move forward on this issue of the MN coming back home.

My intention here is *NOT* to recreate the very lengthy discussions,
but merely to record what I interpret as being the consensus. I'll
add brief explanatory comments, but what's important is to have
the right set of conclusions.

I believe this is that set:

   - MN does DAD targetting its own address.
   - BU to deregister, *not* simple DAD override
   - BU Source address for deregistration is the HoA

A it more info:

1. MN does DAD targetting its own address.

    Suggested by Pascal. This is as opposed to (pre rev20) the MN
    doing a DAD targetting the HA address (which could lead
    to the MN taking over the HA address in some situations).
    The other alternatives involved using a different ICMP
    code (other than 0). Rev20 uses this variation
    of icmp code == 1, and the DAD targetting the home agent addr.

    Overall, this proposal is quite simple and has the added benefit
    that no new icmp codes need be defined.

2. BU to deregister, *not* simple DAD override

   In this proposal, the HA yields the address when
   it hears the 'DAD' from the MN. There were very strong arguments
   against this. I agree this is to be opposed very strongly.
   Proponents argued that ND is already quite weak, so this
   is not a big deal. However, one of the security design goals is
   not to introduce any new or additional weaknesses into the net.
   Once SeND does its job, then this 'override' would remain a
   weakness. No need to do this.

   This decision implies no change.

3. BU Source address for deregistration is the HoA

    Must be cuz the BU has a HAO, and otherwise IPsec will break.
    This is just like all other BU's.

    No change needed.

Comments?

-gabriel

---

From: "Ed Remmell" <[email-masked]>
Date: Tue, 18 Feb 2003 18:51:39 -0800

Gabriel -

>     that no new icmp codes need be defined.

Quick answer:
I'm OK with this.

Details:
I agree Pascal's suggestion is better than BED or DAD of the HA's address.
However, I do not plan to use any of these methods. I'd like something as
close to regular ND as possible, so in our implementation we will always
register with L=0 in the BU (regardless of the home address being
registered). What I've requested to see added to the spec (which from a
previous posting of Jari's it looks like there was agreement) is that the HA
will not defend the derived link-local scope address when the MN registers
by sending a BU with L=0. Then, if we do experience a DAD failure on the
MN's link-local scope address when returning home, we will expect the user
application to recover by setting a random interface ID (i.e. the RFC-3041
functionality specified for recovery from a DAD failure on a foreign link,
we would expect the user application to do the same type of recovery on the
home link) so our MN implementation can successfully auto-configure a
different link-local scope address and then be able to NS the HA per
standard IPv6 Address Resolution procedures so we can then deregister with
it. Anyways, just FYI. I'm not expecting you to recommend this method, since
we have a generic MN implementation specifically for embedded systems where
RAM and ROM usage needs to be minimized as much as possible.

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

---

From: Jari Arkko <[email-masked]>
Date: Thu, 20 Feb 2003 00:51:25 +0200

>   - BU Source address for deregistration is the HoA

Agree.

>    that no new icmp codes need be defined.

Here's the text for this change. In 11.5.4, change

    ... The target of the Neighbor Solicitation
    MUST be set to the home agent's IPv6 address, which is known to the
    mobile node.  The destination IP address MUST be set to the
    Solicited-Node multicast address [3].  The ICMP Code field MUST be
    set to 1 in order to distinguish this solicitation from a similar
    packet that would only be used for DAD, as described in Section 7.5.
    The home agent will send a multicast Neighbor Advertisement back to
    the mobile node with the Solicited flag (S) set to zero.

to

    .. The target of the Neighbor Solicitation
    MUST be set to the mobile node's home address. The destination
    IP address MUST be set to the Solicited-Node multicast address [3].
    The home agent will send a multicast Neighbor Advertisement back to
    the mobile node with the Solicited flag (S) set to zero.

Delete Section 7.5 and the corresponding requirement from 8.4.

Latest draft versions are on the web.

Jari