Hi: Neighbor Discovery is traditionally implemented over multicast. And multicast is more often than not implemented over a plain mac level broadcast. This is the "cry out loud" paradigm, perfectly suited for Ethernet, and totally unsuited for LowPANs.
draft-chakrabarti-6lowpan-ipv6-nd makes a great point on explaining the steps that this takes and the associated cost. I think that this part of the document has already most of the attributes to be turned into a ND problem statement WG doc for 6LoWPAN. What I disagree with is the approach to solve the problem by patching optimizations all over the process. We have to face that the result is still not acceptable and that the whole paradigm should be revised for the LowPAN. In a memory constrained device, implementing MLDv2 is huge overkill, even if its use can be reduced in runtime by refined optimizations. In a same fashion, relying on mesh-under multicast support is unrealistic. At the other end of the routing spectrum from the "cry out loud" paradigm, the "white board" model proposes a solution where one node acts as a reference for all the others. With that model, every node claims an address by writing on the white board and looks up an address by reading from the white board. DAD is a lookup / commit collapsed in a single NS flow. All NS/NA become unicast activity, no MLD, dead simple. And RAs are broadcast. The catch is obviously that the white board is not a fully distributed model. Is that even acceptable? If we consider that LowPANs usually have a sink of some sort, probably a higher-power never-sleeping router, then it makes a lot of sense to use that special node for placing the function. So why not? I tried to capture this idea in http://tools.ietf.org/html/draft-thubert-6lowpan-backbone-router. On top of the white board, the draft adds the capability for the white board to act as a ND proxy and extend the LoWPAN across an IP backbone and potentially scale the PAN into a very large link. Note that the draft was renamed from LoWPAN to 6lowpan but the content is unchanged. So, what do you think? Pascal _______________________________________________ 6lowpan mailing list [email protected] https://www.ietf.org/mailman/listinfo/6lowpan
