Hi Ralph >> 1. In a mesh-under network, the L2 characteristics of the lowpan are >> close to those usually assumed for implementation of IPv6; in >> particular, there are no "lowpan routers" at L3 and L3 messages *can* >> be delivered (perhaps with lower probability of success) directly >> between lowpan nodes. Why is ND not sufficient in this model? > >RFC 4861 ND works in a pure RFC 4944 mesh-under network if: >1) the mesh-under (L2) routing protocol provides subnet-wide multicast, >2) that is efficient enough to be used for routine ND messages, >3) nodes are awake often enough to detect and reply to NS messages. > >Such networks do exist, but these assumptions are not necessarily compatible with many application >scenarios we have in mind; this is the reason we started with ND optimizations.
Another way of saying this is that mesh under is more often than not akin to NBMA. Fully mesh might exist and multicast emulation might exist though I've seen neither so far. But there are actual networks out there where the model is really that of virtual circuits, established either hub and spoke (to a sink) or point to point (control loop). So the model is closer to Frame Relay, for which as we all know 4861 is not better suited than ARP was for IPv4. Issues: * non transitive: A has a circuit to B and B has a circuit to C does not mean A has a circuit to C. Direct (one hop) multicast emulation cannot do DAD. * local addressing: A might not see B with the same address (VC nb) as C sees B. So A could not send redirects to C for B. And SLLAO is useless (same as 3122) if VCs are switched. Our draft can act as a complement to 4861 in transit links (to grant the right to use an address) and a complement to 3122 on NBMA. Our draft is enough for host to router, and the existing ND operation still provide value for host to host. > >> Would >> proxy ND be sufficient? > >I haven't seen such a design yet, so I don't know. Recursing proxy ND demands a strict hierarchy / spanning tree. Could be done but probably difficult and inefficient. This is certainly incapable to handle movement - there were drafts like this in NEMO long ago. Cheers, Pascal _______________________________________________ 6lowpan mailing list [email protected] https://www.ietf.org/mailman/listinfo/6lowpan
