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 Functions Compared to Equivalent IPv4 Functions 1 2 3 IPv6 ND Host-Host Communication Functions: Address Resolution, Next-Hop Determination, Neighbor Unreachability Detection and Duplicate Address Detection

Host-Router Discovery Functions Performed By Routers

The mechanisms for using these messages is not really that complicated. The best way to see how the discovery process works overall is to look at the specific tasks performed both by routers and hosts in ND. Let's start with those performed by routers:

• Routine Advertisement: The main job that routers do in ND is the regular transmission of Router Advertisement messages. Each router maintains a timer that controls how often an advertisement is sent out. Advertisements are also sent when any sort of special situation arises. For example, a message will be sent if key information about the router changes, such as its address on the local network.
  
  Router Advertisement messages include key information about both the router and the network. See the relevant topic in the ICMPv6 section for a full description of the Router Advertisement message format.
  
  
• Parameter Maintenance: Routers are responsible for maintaining key parameters about the local network so they can be sent in advertisements. These include the default Hop Limit that should be used by hosts on the network, a default MTU value for the network, and information such as network prefixes that are used for both first-hop routing by hosts and autoconfiguration.
  
  Again, some more details on these can be found in the topic that discusses Router Advertisement fields.
  
  
• Solicitation Processing: Routers listen for Router Solicitation messages and when one is received, will immediately send a Router Advertisement to the requesting host.

IPv6 ND Functions Compared to Equivalent IPv4 Functions 1 2 3 IPv6 ND Host-Host Communication Functions: Address Resolution, Next-Hop Determination, Neighbor Unreachability Detection and Duplicate Address Detection