Neighbor Discovery Protocol

The Neighbor Discovery Protocol (NDP) is a protocol in the Internet Protocol Suite used with Internet Protocol Version 6 (IPv6). It operates in the Internet Layer of the Internet model (RFC 1122) and is responsible for address autoconfiguration of nodes, discovery of other nodes on the link, determining the Link Layer addresses of other nodes, duplicate address detection, finding available routers and Domain Name System (DNS) servers, address prefix discovery, and maintaining reachability information about the paths to other active neighbor nodes (RFC 4861).

The protocol defines five different ICMPv6 packet types to perform functions for IPv6 similar to the Address Resolution Protocol (ARP) and Internet Control Message Protocol (ICMP) Router Discovery and Router Redirect protocols for IPv4. However, it provides many improvements over its IPv4 counterparts (RFC 4861, section 3.1). For example, it includes Neighbor Unreachability Detection (NUD), thus improving robustness of packet delivery in the presence of failing routers or links, or mobile nodes.