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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

Host-Router Discovery Functions

One of the two main groups of functions in ND are those that facilitate the discovery of local routers and the exchange of information between them and hosts. This includes four specific functions:

• Router Discovery: This is the core function of this group: the method by which hosts locate routers on their local network.
  
  
• Prefix Discovery: Closely related to the process of router discovery is prefix discovery. Recall that the term “prefix” refers to the network portion of an IP address. Hosts use this function to determine what network they are on, which in turn tells them how to differentiate between local and distant destinations and whether to attempt direct or indirect delivery of datagrams.
  
  
• Parameter Discovery: Also closely related to router discovery, this is the method by which a host learns important parameters about the local network and/or routers, such as the maximum transmission unit of the local link.
  
  
• Address Autoconfiguration: Hosts in IPv6 are designed to be able to automatically configure themselves, but this requires information that is normally provided by a router.

The other main group of functions is that associated with information determination and communication directly between nodes, usually hosts. Some of these functions can be performed between hosts and routers, but this group is not specifically related to router discovery; it includes:

• Address Resolution: The process by which a device determines the layer two address of another device on the local network from that device's layer three (IP) address. This is the job performed by ARP in IP version 4.
  
  
• Next-Hop Determination: The method for looking at an IP datagram's destination address and determining where it should next be sent.
  
  
• Neighbor Unreachability Detection: The process of determining whether or not a neighbor device can be directly contacted.
  
  
• Duplicate Address Detection: Determining if an address that a device wishes to use already exists on the network.

The last functional group contains just one function: Redirect. The technique whereby a router informs a host of a better next-hop node to use for a particular destination.

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