Re: [DNA] Considerations for DNA Schemes with multiple Interface andLayer 2 Technologies

[Pekka Nikander <pekka.nikander@nomadiclab.com>]

>> Purely DNA point of view, it would be better if CDMA doesn't support 
>> 'make-before-break' at all. It would make DNA much simpler.
>
> I know this was a throw-away line, but it's hard to throw away.
>
> I think that MBB will have to be supported, in DNA.  This is especially
> the case where Unreachability is to be determined from certain tests.
>
> We mainly need to be clear about which tests are applicable and
> what inference is taken from received messages.  I think this
> is still in coverage for the BCP and Goals though.

I have to admit that I am totally confused now.  Maybe I just
don't know the facts.  So, let me ask some stupid questions:

1. Are people planning to use make-before-break with CDMA
    with PPP or not?  Or both?  (If PPP is used, I see no
    problem wrt. DNA as PPP is then the link layer to IPv6,
    and the situation has to be handled below the IPv6 layer.)

2. Assuming no PPP is used, are there any actual plans of
    supporting make-before-break between networks that actually
    have different IPv6 configuration at different base stations?
    (If not, again, I don't see what we have to worry about.)

3. Assuming no PPP is used and make-before-break is supported
    between base stations that potentially have different
    network configuration, is there any reason why the link
    layer cannot model the situation as two different interfaces?

That is, even in the case that the CDMA link layer does not use
PPP but is directly visible to IPv6, if we can model the radio
layer connections to different base stations as different interfaces,
as seen by IPv6, I don't see any problem.  The worst that can there
happen is that the two interfaces, corresponding to the two radio
layer connections, are connected to the same IPv6 network.  But that
is a case that we have to handle otherwise, too.

There may be some problems related to link layer addresses, etc,
but someone should really point us to the right documents, or better,
write a problem statement draft of the situation, trying to clarify
the current plans of running IPv6 over make-before-break CDMA (and
other such radio links).  I don't see much use to argue about this
until we properly understand the details, and at least I can't
possibly claim understanding them.  I don't even know what documents
I should read; sorry about my ignorance.

--Pekka