Subject: but isn't wifi fundamentally unsuited for low-power networks anyway?

From: "Pascal Thubert (pthubert)" <[email-masked]>
Date: Wed, 27 Nov 2013 15:07:07 +0000

Hi Lorenzo:

Wrong, actually. Low Power WiFi has been part of the spec since about forever. Philips is shipping LP-WiFi light bulbs that will associate to your standard WiFi AP at home.

The way is works is that the device (the light bulb) polls the AP went it awakes. The AP must stay online but the device can sleep. This is a typical case where we'd want the "L3 AP" (== a backbone router) proxying for the device with its own MAC address so as to attract the packets for the device and keep them in store till the device wakes and polls for them.

This is one of the modes that WiND enables in the registration, and the value of the registration here is similar to that of Mobile IP. Like an HA, the BBR proxies ND on behalf of the device so that in this case the device can stay asleep; the BBR also filters link scope ND broadcasts that are coming from nodes that support classical ND in mixed mode and dutifully unicasts its RAs when the device wakes.

It is up to the device to request in its ARO option whether it wants its MAC address exposed by the BBR in the ND proxy operation. We expect not for low power devices. Mobile Phones could be different. We (cisco) are already doing that sort of things for all sorts of WiFi clients in our controllers and switches using states that are snooped by first Hop Security (SAVI), and so far we proxy with the address of the device.

There are limits to what you can do with snooping and a standard registration would be a welcome step to protect the wireless devices against the consequences of a protocol that was not designed for them.

Cheers,

Pascal

From: Lorenzo Colitti [mailto:[email-masked]]
Sent: jeudi 21 novembre 2013 09:10
To: Pascal Thubert (pthubert)
Cc: Erik Kline; Ole Troan; 6man Chairs; 6man WG
Subject: Re: 6MAN Adoption call on raft-chakrabarti-nordmark-6man-efficient-nd-04

On Thu, Nov 21, 2013 at 3:40 AM, Pascal Thubert (pthubert) <[email-masked]<mailto:[email-masked]>> wrote:
So clearly, as we build a multilink subnet with 802.15.4 at the edge, we must place a router - called backbone router in ISA100.11a - between the .1 and the .15.4 links. You will note that even in that case, we need the registration mechanism to perform DAD - RFC 6775 was initially designed in that context -, and that proxy ND can be used at the backbone router, as discussed in the original ML subnet draft by Dave and Christian.

If you're routing, why do you need proxy ND? Just give the 802.15.4 network a separate /64 and run 6LoWPAN ND inside it.

I think that's when Erik says "merging two link types is not the solution", that's what he means. I think he's just suggesting that you use existing standard ND in the high-powered network and existing 6LowPAN ND in the low-power network, and just route between them. That way you don't have to define a new ND protocol.

Now, WiFi does not qualify as 'a different link type' that would require routing to Ethernet; on a same AP, some clients may be low power

Well, but isn't wifi fundamentally unsuited for low-power networks anyway? It's got beacons going all the time, it has multicast, etc.

We do not want to renumber each time a device re-associates to the next AP, so we care for a rather large subnet. And there, it is not just a problem of implementing multicast at layer 2 in a fashion  that serves solicited node mcast addresses, placing the burden on another layer that, as it goes, does not have the adapted support in place...

You don't have to change ND to do that. All you need to do is either use solicited-multicast node addresses over the multicast channel or, if the subnet is SO large that ND requests are overwhelming (but that seems like a LOT of ND traffic - how many clients do you need before this starts happening?), use MLDv2 snooping and send the NS packets L2 unicast to their destination.

There is also the need for much faster DAD (not based on timing out)

What's the use case for faster DAD if you have optimistic DAD?