Re: [DNA] New I-D: draft-vogt-dna-relocation-00.txt

[Erik Nordmark <erik.nordmark@sun.com>]

Brett Pentland wrote:

> Ah yes.  For some reason a forgot that the MN would be the one
> initiating the communication.  Is there any way that an on-link
> node could obtain the MN's CoA and try to initiate a
> communication?

I decided to walk through the details for the case when a CN on a link 
and the MN moves to that link, and does RO with the CN.

The steps would be:
1. MN uses DNA to detect that it has moved; sees a link up notification, 
and sends an RS (address is optimistic)
2. Receives an RA which indicates that it has moved.
3. Sends a BU to the HA. Initiates the BU process with the CN by sending 
a CoTI (and HoTI). The CoTI is sent from the CoA to the CN's address, 
thus it triggers the NS/NA exchange with the CN.
4. CN receives the HoTI and responds with a HoT. Receives the CoTI at 
about the same time. Tries to send a CoT. Has the neighbor cache entry 
for the CoA from the NS it received in #3.

Looks ok.

But if the CN was really a MN (MN2) (i.e., we have two MNs which have 
moved to the same link), then the CoTI wouldn't be sent to the HoA2, and 
tunneled by HA2 to CoA2. Thus in #3 there wouldn't be a NS/NA exchange - 
the CoTI would be sent to HA2 (which we assume is off link).

But even in that case I think we are ok; the CoT will be sourced by MN2 
with HoA2 as the source address, thus MN2 will reverse tunnel it via 
HA2. Hence MN2 doesn't need a neighbor cache entry in #4.

Later (step 5) the MN sends the BU from CoA to CoA2, which makes it do a 
NS/NA exchange to find the link layer address for CoA2.

I guess one can do similar analysis for other RO schemes, but it might 
be a bit tedious.

One can instead argue that if the MN sends the MLD report as part of #3, 
even if it is sent after the other messages in #3, then the probability 
that something will try to do a NS/NA exchange with the MN before the 
MLD report is sent is very small. And should that ever happen, then the 
fact that the NS will be retransmitted after 1 second should take care 
of things.

So in summary, it's ok as long as the MLD report is sent "early", even 
if it isn't sent first.

    Erik