The IPv6-over-IEEE 802.15.4 [RFC4944] document specifies how IPv6 is carried over an IEEE 802.15.4 network with the help of an adaptation layer that sits between the Media Access Control (MAC) layer and the IP network layer. A link in a Low-power Wireless Personal Area Network (LoWPAN) is characterized as lossy, low-power, low-bit-rate, short-range; with many nodes saving energy with long sleep periods. Multicast as used in IPv6 Neighbor Discovery (ND) [RFC4861] is not desirable in such a wireless low-power and lossy network. Moreover, LoWPAN links are asymmetric and non-transitive in nature. A LoWPAN is potentially composed of a large number of overlapping radio ranges. Although a given radio range has broadcast capabilities, the aggregation of these is a complex Non-Broadcast Multiple Access (NBMA) [RFC2491] structure with generally no LoWPAN-wide multicast capabilities. Link-local scope is in reality defined by reachability and radio strength. Thus, we can consider a LoWPAN to be made up of links with undetermined connectivity properties as in [RFC5889], along with the corresponding address model assumptions defined therein. This specification introduces the following optimizations to IPv6 Neighbor Discovery [RFC4861] specifically aimed at low-power and lossy networks such as LoWPANs:
o Host-initiated interactions to allow for sleeping hosts. o Elimination of multicast-based address resolution for hosts.
o A host address registration feature using a new option in unicast Neighbor Solicitation (NS) and Neighbor Advertisement (NA) messages.
o A new Neighbor Discovery option to distribute 6LoWPAN header compression context to hosts.
o Multihop distribution of prefix and 6LoWPAN header compression context.
o Multihop Duplicate Address Detection (DAD), which uses two new ICMPv6 message types.
The two multihop items can be substituted by a routing protocol mechanism if that is desired; see Section 1.4.