Routing and device discovery in Wi-SUN rely on two key IPv6 coordination mechanisms:

These mechanisms work together to support routing, address resolution, and network maintenance across the mesh.

Multicast in context

Wi-SUN uses IPv6 multicast as the transport for NDP and other control protocols such as RPL and DHCPv6. Each device automatically subscribes to the multicast groups relevant to its role (for example, all routers or all nodes).

For detailed information about multicast address types and scopes, see Multicast addresses.

Neighbor Discovery Protocol (NDP)

NDP is a fundamental part of IPv6 networking that allows Wi-SUN devices to identify and communicate with nearby nodes. It provides the foundation for neighbor awareness, address resolution, and reachability in the mesh.

Key functions of NDP include:

  • Discovering nearby neighbors.

  • Determining link-layer (MAC) addresses.

  • Detecting unreachable devices.

  • Autoconfiguring routes and prefixes.

NDP relies on IPv6 link-local and multicast communication to exchange control messages. Key NDP message types include:

  • Neighbor Solicitation (NS): Sent by a device to find the MAC address of another IPv6 address.

  • Neighbor Advertisement (NA): Sent in response to an NS, containing the MAC address.

  • Router Advertisement (RA): Sent by routers (e.g., the border router) to announce prefixes.

  • Router Solicitation (RS): Sent by nodes to request RAs from routers.

Wi-SUN leverages 6LoWPAN optimizations to compress and minimize NDP traffic, improving performance on constrained links and does not use the RA/RS NDP messages. In Wi-SUN routing is entirely managed by RPL.