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The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  TCP/IP IPv6 Neighbor Discovery Protocol (ND)

IPv6 ND Overview, History, Motivation and Standards 1 2 3 IPv6 ND Functions Compared to Equivalent IPv4 Functions

Relationships Between Functions

The division of ND's overall functionality into nine tasks in three groups is somewhat arbitrary, but provides a good frame of reference for understanding what the protocol does. Obviously some of the functions in different groups are related; next-hop determination uses information obtained as part of parameter discovery. The redirect function is also a form of router-host communication but is distinct from router discovery.

Just as ND is similar to ICMP in its operation, the two protocols are related in another way: the method that messaging is done. ND actually implements its functions using ICMPv6 messages. A set of five message types is described in the ND standard:

• Router Advertisement Messages: Sent regularly by routers to tell hosts that they exist and provide important prefix and parameter information to them.
  
  
• Router Solicitation Messages: Sent by hosts to request that any local routers send a Router Advertisement message so they don't have to wait for the next regular advertisement message.
  
  
• Neighbor Advertisement Messages: Sent by hosts to indicate the existence of the host and provide information about it.
  
  
• Neighbor Solicitation Messages: Sent to verify the existence of another host and to ask it to transmit a Neighbor Advertisement.
  
  
• Redirect Messages: Sent by a router to tell a host of a better method to route data to a particular destination.

More details on how these message types are used can be found in the topics later in this section that describe the three functional groups above in more detail. The structures of each of the five ICMPv6 message types used by ND can be found in the section on ICMPv6 informational message types and formats.

IPv6 ND Overview, History, Motivation and Standards 1 2 3 IPv6 ND Functions Compared to Equivalent IPv4 Functions