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The Neighbor Discovery Protocol (NDP) is a protocol in the Internet Protocol Suite used with IPv6. It operates in the Link Layer and is responsible for discovery of other nodes on the link, determining the link layer addresses of other nodes, finding available routers, and maintaining reachability information about the paths to other active neighbor nodes (RFC 4861, 2007).[1]

NDP performs functions for IPv6 similar to the way Address Resolution Protocol (ARP) and ICMP Router Discovery and Router Redirect protocols do for IPv4. However, it provides many improvements over its IPv4 counterparts (see 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. NDP is more media (link type) independent than ARP.

The Internet Protocol Suite
Application Layer
BGP · DHCP · DNS · FTP · GTP · HTTP · IMAP · IRC · Megaco · MGCP · NNTP · NTP · POP · RIP · RPC · RTP · RTSP · SDP · SIP · SMTP · SNMP · SOAP · SSH · Telnet · TLS/SSL · XMPP · (more)
Transport Layer
TCP · UDP · DCCP · SCTP · RSVP · ECN · (more)
Internet Layer
IP (IPv4, IPv6) · ICMP · ICMPv6 · IGMP · IPsec · (more)
Link Layer
ARP/InARP · NDP · OSPF · Tunnels (L2TP) · PPP · Media Access Control (Ethernet, DSL, ISDN, FDDI) · (more)

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 Internet parameters (e.g., MTU).
  • Address Autoconfiguration: stateless configuration of addresses for an interface.
  • Address Resolution: mapping from IP address to link-layer address.
  • 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 node about better first-hop.

NDP defines the following five different ICMPv6 packet types:[2]

  • Router Solicitation
  • Router Advertisement
  • Neighbor Solicitation
  • Neighbor Advertisement
  • Redirect

See also


  1. ^ RFC 4861, Neighbor Discovery for IP version 6 (IPv6), T. Narten et al., September 2007
  2. ^ RFC 2461, Neighbor Discovery for IP version 6 (IPv6), T. Narten, December 1998


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