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

[Greg Daley <greg.daley@eng.monash.edu.au>]

Hi Paul,

I've responded to your email, but there may
be rhetorical questions in the text (sorry).

Paul Tan wrote:
> Hi Alper,
> 
> Alper Yegin wrote:
> 
>>If the STA is going to perform a reachability test in any case, 
>>
> If the station have discovered the *prefix(es)* associated with an AP 
> earlier during its neighborhood discovery phase, and assuming that it 
> finally associates with this AP, do you think *reachability test* is 
> necessary ?

I think it is necessary, because the configuration's presence
on the AP doesn't mean that the router is up, reachable or
working correctly.

There's a WLAN accesspoint down the corridor from me which is
a black hole for people walking past it accepts their connections
and then doesn't route. Why? because there is no ethernet plugged in.

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.

>>what is the functionality of learning the possible prefixes? 
>>
> As I specified in my draft, the original purpose of these *advertised 
> prefix(es)* is to enhance Movement Detection operation. There might be 
> other possible use-cases ...can I pre-configure/verify a CoA (plus DAD) 
> for this prefix in advance or maybe *initialise* a fast-handoff operation.

I don't think so.

A lot of people have tried to get this (a way around DAD using
network state).  It's quite hard to do.

What's more likely to be the case here is that authentication
could imply MAC address uniqueness, but still this doesn't
imply that someone else hasn't configured your I-ID.

> Imagine having a bunch of long network cables, each connected to 
> different subnets. However, these cables are tagged physically with a 
> *prefix* tag, in this case, you simply choose your choice of subnet and 
> plug it into your device.

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.

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

Perhaps, but I think that such a protocol looks like
something able to be better handled by CAPWAP than DNA.
We'd have to agree in that case, what we'd need from the
automatically configured AP.

Greg