ICMPv6 messages

The IPv6 Neighbor Discovery Protocol (ND) consists of five types of ICMPv6 messages:

  • Neighbor Solicitation (NS) - An IPv6 node (a host or network device running IPv6) sends NS packets to obtain the link-layer addresses of its neighbors and to detect neighbor reachability and duplicate addresses.

  • Neighbor Advertisement (NA) - An IPv6 host sends an NA packet in response to an NS packet. An IPv6 node also sends NA packets when the link-layer topology changes.

  • Router Solicitation (RS) - When an IPv6 node starts, it sends an RS packet to a router to request prefixes and other configuration information, and waits for the router to respond with an RA packet.

  • Router Advertisement (RA) - A router periodically advertises RA packets, including network configurations such as network prefix to IPv6 nodes. The router also returns RA packets as the responses to RS packets.

  • Redirect (RR) - When detecting that the inbound interface and outbound interface of a packet are the same, a router sends a Redirect packet to request the IPv6 node to select a better next hop address.

These ICMPv6 messages help to achieve these five functions:

  • address resolution

  • neighbor reachability detection

  • router/prefix discovery

  • address auto-configuration

  • redirection