Hi Luis, thanks for bringing this question to the mailing list. Specifications are sometimes like trapdoor functions: If you already know what's in there, they are quite clear, but it is difficult to find an answer to a question. Maybe we can add some more explanatory text.
On Dec 6, 2010, at 14:52, Luis Maqueda Ara wrote: > a) How does a host send a packet to another neighboring host? 6LoWPAN-ND doesn't give you this capability. As you cited, all addresses are considered off-link, so you always go through a router. > b) Should hosts maintain NCEs for other hosts? If so, under which > circumstances would these NCEs be created? Corollary: The answer is no. Why is this a sensible approach? Of course, it is a design decision, with the usual trade-offs. The rationale is approximately: If a node is capable of maintaining relationships to multiple other nodes, it might as well be a router. The routing protocol will provide a way to maintain neighborhood relationships that is more powerful than the simplistic 6LoWPAN-ND. (Note that being a router does not have to mean that you accept packets that are actually routed through you -- it just means you participate in routing. E.g., in RPL, there is a concept of a "leaf node".) Really simple nodes restrict themselves to a host role. They use 6LoWPAN-ND (and, in particular, NUD) to maintain a default-router relationship to a router (or possibly two or three routers, if desired for additional robustness). They use their default router to talk to other hosts. There may be 6LoWPANs that do not have any host-only nodes. (According to various IETF hallway discussions, this model appears to a preferred model for some, but not all RPL advocates.) Router nodes may still use 6LoWPAN-ND in their bootstrapping processes, as well as a mechanism to talk to hosts (if they want to provide forwarding services for those). Gruesse, Carsten _______________________________________________ 6lowpan mailing list [email protected] https://www.ietf.org/mailman/listinfo/6lowpan
