Re: [DNA-BOF] Using L2 to provide Instantaneous MD & ND

[Bernard Aboba <aboba@internaut.com>]

> Also the reachability based on reception of broadcast beacons
> is not sufficient to determine that the AP can hear your transmissions.
> Probe-Request/Response may work, as will authentication,
> but not passive beacon reception.

On the fringes of coverage it is possible for a station to be able to hear
the Beacons and Probe Responses and possibly even to successfully complete
an Association/Reassociation exchange.  However, attempting to send
substantial amounts of data will fail.

In general the reachability test is *essential* because L2 hints are
intrinsically fallible.  We have learned this lesson in many painful ways
over the years.

> Certainly there is value in receiving indications which
> help distinguish L2 or L3 handover events.
> Unless there is a predictable protocol and standard for
> deploying such prefix information, it will always
> have to be considered a 'weak' hint.

I'd argue that even if there were a standard, that the "hint" would still
be "weak" -- by which I mean that a reachability test would still be
required to confirm it.

> Is it worth having a standard way to provide this
> information, so that we can guarantee that it gives a
> strong hint?

I don't think that a standard can by itself make the hint strong.  You'd
have to make the probability of a misleading hint negligible, so that a
reachability test could be dispensed with.  An example of a strong hint
might be a cached RA that is only dispensed when the station has been
securely associated to the VLAN that it was received from.  Note that
nothing like this has yet been proposed in IEEE 802.

> Perhaps, but I think that such a protocol looks like
> something able to be better handled by CAPWAP than DNA.

CAPWAP is defining a "split" AP model.  It is not dealing with handoff
optimization.  That is the task of the IEEE 802 Handoff Executive
Committee Study Group (ECSG).