Subject: [MOBILE-IP] Swapping care-of address and home address

From: "Charles E. Perkins" <[email-masked]>
Date: Thu, 9 Nov 2000 09:26:33 -0800

Hello folks,

Here's another conundrum that has to be settled.

Problem:
        How is AH calculated when care-of address is
        initially present in the IPv6 header, and the
        Home Address option is present.

Proposal:
        Exchange the care-of address in the IPv6 header
        with the home address in the Home Address option.
        Then, when AH is calculated on the receiving end,
        the care-of address will be present in the data
        field of the Home Address option, and the home
        address will be present in the IPv6 header.

Also:
        When the Binding Update is present, a Home Address
        option is mandatory.  The above proposal means that
        when the inbound Binding Update processing occurs,
        the care-of address has to be retrieved from the
        Home Address option instead of the IPv6 header.

Thinking about the alternatives, while required, is enough
to give one a migraine headache.  For those who dare go on,
please don't say I didn't warn you.

Alternative 1: Keep both in place
        This means that all subsequent processing has to be
        special cased depending on whether or not a Home
        Address option has been processed.  The code I have
        seen (e.g., protocol-switch based code) has a hard
        time dealing with this.

Alternative 2: Copy the home address into the IPv6 header,
        and do not copy the care-of address into the Home
        Address option.  This doesn't simplify anything, and
        just makes it harder to retrieve the care-of address.

I'm not exactly sure whether there has already been agreement
on this or not.  I know there's been plenty of discussion.
There seems to be three main camps:
        - Leave the fields where they are, and
        - Exchange them
        - Do almost anything reasonable, but pick something
          definite and make it mandatory.

I hope this qualifies to satisfy those in the last two camps,
at least.  And, I think that there is general agreement that
the current wording of the draft has to be changed somehow
to make it clear which alternative is being specified.

Regards,
Charlie P.

---

From: Vijay Devarapalli <[email-masked]>
Date: Thu, 9 Nov 2000 10:25:00 -0800

>         just makes it harder to retrieve the care-of address.

The CoA is not protected by AH in this case.

Vijay

---

From: "mohan.parthasarathy" <[email-masked]>
Date: Thu, 9 Nov 2000 18:54:54 -0800

Charlie,

All we need to do is protect both the CoA and the Home Address.
It does not really matter where these addresses are found i.e
whether it is found in the Ipv6 header or the Home Address option.

For AH calculation to be same on both the sending and
receiving side, we need to define what the Ipv6 source address
would contain and what the home address option would contain.
To keep the draft simple, i suggest the following :

"While computing the AH, the Ipv6 source address field MUST
 contain the Home address and the Home address option MUST
 contain the Care of Address."

How you achieve the above is implementation dependent.

-mohan