The Neighbor Discovery Protocol (NDP) is a protocol in the Internet Protocol Suite

Internet protocol suite

The Internet protocol suite is the set of communications protocols used for the Internet and other similar networks. It is commonly known as TCP/IP from its most important protocols: Transmission Control Protocol and Internet Protocol , which were the first networking protocols defined in this...

 used with Internet Protocol Version 6

IPv6

Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...

 (IPv6). It operates in the Link Layer

Link Layer

In computer networking, the link layer is the lowest layer in the Internet Protocol Suite , the networking architecture of the Internet . It is the group of methods or protocols that only operate on a host's link...

 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

Domain name system

The Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities...

 (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

Address Resolution Protocol

Address Resolution Protocol is a telecommunications protocol used for resolution of network layer addresses into link layer addresses, a critical function in multiple-access networks. ARP was defined by RFC 826 in 1982. It is Internet Standard STD 37...

 (ARP) and Internet Control Message Protocol

Internet Control Message Protocol

The Internet Control Message Protocol is one of the core protocols of the Internet Protocol Suite. It is chiefly used by the operating systems of networked computers to send error messages indicating, for example, that a requested service is not available or that a host or router could not be...

 (ICMP) Router Discovery

ICMP Router Discovery Protocol

ICMP Internet Router Discovery Protocol uses Internet Control Message Protocol router advertisements and router solicitation messages to allow a host to discover the addresses of operational routers on the subnet....

 and Router Redirect

ICMP Redirect Message

The ICMP type 5 contains a redirect message to send data packets on an alternative route. ICMP Redirect is a mechanism for routers to convey routing information to hosts. The Redirect Message is an ICMP message which informs a host to update its routing information...

 protocols for IPv4

IPv4

Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...

. 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.

Technical details

The Neighbor Discovery Protocol defines mechanisms for providing the following functionality:

• Router discovery: hosts can locate routers residing on attached links.
• Prefix discovery: hosts can discover address prefixes that are on-link for attached links.
• Parameter discovery: hosts can find link parameters (e.g., MTU
  Maximum transmission unit
  In computer networking, the maximum transmission unit of a communications protocol of a layer is the size of the largest protocol data unit that the layer can pass onwards. MTU parameters usually appear in association with a communications interface...
  
  ).
• Address autoconfiguration: stateless configuration of addresses of network interfaces.
• Address resolution: mapping between IP addresses and link-layer addresses.
• Next-hop determination: hosts can find next-hop routers for a destination.
• Neighbor unreachability detection (NUD): determine that a neighbor is no longer reachable on the link.
• Duplicate address detection (DAD): nodes can check whether an address is already in use.
• Redirect: router can inform a node about better first-hop routers.
• Recursive DNS Server (RDNSS) and DNS Search List (DNSSL) assignment via a router advertisement (RA) options. This is a new feature and not widely supported by clients.

NDP defines the following five ICMPv6

ICMPv6

Internet Control Message Protocol version 6 is the implementation of the Internet Control Message Protocol for Internet Protocol version 6 defined in RFC 4443...

packet types:Router Solicitation, Router Advertisement, Neighbor Solicitation, Neighbor Advertisement, and Redirect.

External links

• Neighbor Discovery Protocol