Re: [DNA] [Issue 15] [Issue 16] DAD and MLD Interaction

[James Kempf <kempf@docomolabs-usa.com>]

> Or. more generally, until it has determined that it has moved to a new
> link. If an RS is returned which indicates that it didn't move, then
> there is no need to send an RS.
>

You mean "no need to send an NS" I think.

Well, there is unfortunately an off chance that, while the host is in
transit from one wireless AP to another, someone comes on the link, sends
out one NS to DAD an address that the in-transit host had claimed, and gets
back no response. The new host would therefore conclude that the address was
not a duplicate, but when the in-transit host came back on the link, it
would be a duplicate. Considering the low probability of a collision in
general (which is what makes oDAD statistically possible in the first
place), this case is even more wildly unlikely, but it is still not
completely impossible. :-(

> > Note that even if we do change the state to Optimistic, there is still
the
> > issue I raised about the node originating packets with a topologically
> > incorrect source address if it has moved to a new IP link. The only way
to
> > prevent that from happening is to make the addresses Tentative (and
suppress
> > the DAD NS until after the RA returns) until the node actually finds out
in
> > the RA whether it actually has moved to a new IP link or not.
>
> Originating such packets is ok I think. If the host has moved to a new
> link it will not receive any "replies". It might make sense and assume
> that it didn't move in this case until it's discovered that it did move.
>

OK. So moving to Optimistic prior to sending the RS rather than to Tentative
is probably OK. I think this aligns with what I mentioned in my response to
Nick, that handling packets sent to an address while the host is in transit
is out of scope for DNA.

Do you think making the addresses Deprecated on Link Down is OK, like Nick
suggested? This would prevent any new applications from opening sockets on
them. If the host is multi-interface, these sockets would be directed to a
Confirmed or Optimistic address on another interface, which might or might
not be a benefit.

            jak