Neighbour discovery is a protocol that allows different nodes on the same link to advertise their existence to their neighbours, and to learn about the existence of their neighbors. It is a basic functionality all implementations of IPv6 on any platform must include.

Neighbor discovery for IPv6 replaces the following IPv4 protocols: router discovery (RDISC),Address Resolution Protocol (ARP) and ICMPv4 redirect.

Neighbor discovery is defined in the following documents:

• RFC 2461, Neighbor Discovery for IP Version 6 [RFC2461]
• RFC 2462, IPv6 Stateless Address Autoconfiguration [RFC2462]
• RFC 2463, Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 Specification. [RFC2463]

RFC 2461 and 2462 are currently in the process of being revised by the IPv6 working group of the IETF. These drafts [RFC2461bis], [RFC2462bis] will eventually replace the older RFCs. The combination of these protocols allow IPv6 hosts to automatically detect the presence of other hosts on the link including, of course, the presence of on-link routers. From the messages sent by routers, IPv6 hosts can automatically configure themselves with appropriate addresses and other state necessary for operation. Neighbour Discovery mandates duplicate address detection so that a host cannot try to use an IPv6 address already in use by another host on the link and also allows a host to detect when another host on the link becomes unreachable.

Neighbor discovery uses the following Internet Control Message Protocol Version 6 (ICMPv6) messages:

• router solicitation (RS)
• router advertisement (RA)
• neighbor solicitation (NS)
• neighbor advertisement (NA)
• redirect.