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: [email protected]
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