Unsure about your profile, Mikael. Ethernet would be a #2 by now, only things like sat-links could still be #1s. So the work would really be to figure out what to do with the varieties of your #2. My question is rather whether IP over 802.11 should be operated like IP over Ethernet or like IP over 802.15.4.
Trouble is, some multicast ore more important than others. E.g. you miss an RA, usually no harm done, wait for the next or RS to force one. You missed a DAD, the protocol failed. If we start retrying DADs, we make the broadcast situation even worse. So to your point about energy, Wi-Foo may decide to broadcast some messages, unicast others multiple times, and at some point change the IP protocols so that the protocols operate differently. The IETF already made these steps for 802.15.4. RAs are still broadcasted but DAD was changed to be reliable and unicast-based. The multilink subnet is not one /64 per wireless device as you indicate. That model certainly works too, and was deployed, but with it, a set of 64 bits identifies and routes to a device, so we are mostly back to a world of IPv4 with just DHCP (PD) and identifiers of 64 bits instead of 32. The multilink subnet is a single large subnet encompassing the whole ESS, Ethernet + Wi-Fi. It is really a Layer-3 ESS, based on the same ideas as the Layer-2 is. In that model, the association of a wireless device associates the IP unicast and multicast addresses with the MAC address, and the AP acts as a router and performs proxy ND over the Ethernet backbone on behalf of the wireless devices. That way, the ND NS are never multicast over the wireless. In practice, the association of IP addresses should be done as part of ND, and that is what RFC 6775 does. Cheers, Pascal Cheers, Pascal > -----Original Message----- > From: Mikael Abrahamsson [mailto:swm...@swm.pp.se] > Sent: lundi 10 août 2015 13:03 > To: Pascal Thubert (pthubert) <pthub...@cisco.com> > Cc: ieee-ietf-co...@ietf.org; Dan Romascanu (droma...@avaya.com) > <droma...@avaya.com>; Stephens, Adrian P > <adrian.p.steph...@intel.com>; Glenn Parsons > <glenn.pars...@ericsson.com>; mbo...@ietf.org; Homenet > <homenet@ietf.org>; Eric Gray <eric.g...@ericsson.com> > Subject: RE: [ieee-ietf-coord] Multicast on 802.11 > > On Mon, 10 Aug 2015, Pascal Thubert (pthubert) wrote: > > > Yes it is. IP over Foo must indicate if IP multicast over a link uses L2 > mechanisms or not. > > Ok, so am I interpreting you correctly that there are three profiles for > L1/L2 mediums: > > 1. Multicast works approximately the same way as unicast (packet loss) 2. > Multicast works worse than unicast and should be minimized 3. Multicast > not supported > > So what we're missing is taking into account the #2 profile in the IETF, > because so far we've only really understood that #1 and #3 exists? > > > For Wi-Fi, there is no multicast support and it is sufficiently clear now > > that > relying on broadcast is not a good idea. > > But I keep hearing from the 802.11 experts (at least they seem to be) that > there are 802.11 mechanisms that seem to make multicast work well > enough and that there are power upsides to using multicast? > > > Rather, a good idea could be to build a multilink subnet with APs that > > are also routers to serve the wireless edge, whereby the Ethernet > > backbone can rely on L2 broadcast while the wireless edge is routed. > > Many LLNs work like this. Why should Wi-Fi be an exception? > > Well, I am not wireless expert, I don't know if it makes more sense to treat > each device to its own subnet and thus send RAs to each and every one of > them as needed, or if it makes sense to have some kind of multicast > mechanism and make sure that they all get this multicast packet in a shared > subnet. Your suggestion seems perfectly fine for me from an IP point of > view, actually I prefer that option as well. Basically each host has its own > /64. > > > I'd hate this, IEEE telling IETF what to do. Just like IETF telling > > IEEE to do an immensely scalable L2 multicast support so that > > Solicited Node Multicast appears so cool on a switched fabric? Does > > not seem to work either. > > > > The IETF has to decide if it wants to design IP over 802.11 - or > > Wi-Foo in general which would be my take. And then the IETF has to > > decide if it wants to design IP over a mix of Wi-Fi and Ethernet. IEEE > > people may join the effort so we do the job right. > > Are there more types of profiles we need? Does it make more sense to send > a multicast packet if there are more (or less) than X nodes in a subnet, send > unicast to each and every one of them if it's less (or more) than Y. > Should each individual device be able to say what it prefers in case we're > mixing battery powered devices and wired devices in the same place? > > -- > Mikael Abrahamsson email: swm...@swm.pp.se _______________________________________________ homenet mailing list homenet@ietf.org https://www.ietf.org/mailman/listinfo/homenet
