Router Discovery is achieved through the receipt of a router advertisement sent from an on-link router. This will either be in the form of a router advertisement sent periodically to the all nodes multicast address, or in response to a router solicitation sent by the IPv6 host.

Router advertisements can contain a list of prefixes. These prefixes are used for stateless address autoconfiguration of hosts on the link and to maintain a database of on-link prefixes as well as for duplicate address detection. For routers the list of prefixes, which are on-link is used for forwarding decisions. If the destination address in an IP packet belongs to an on-link prefix, the router forwards the packets to that node. If the node is not on-link, the packets are sent to the next router for consideration. For IPv6 router advertisements, each prefix in the prefix list can contain a prefix length, valid lifetime for the prefix, preferred lifetime for the prefix, an on-link flag and an autoconfiguration flag. This information enables address autoconfiguration and the setting of link parameters such as maximum transmission unit (MTU) size and hop limit.

To summarise, router advertisement messages typically include the following information:

• One or more on-link IPv6 prefixes that nodes on the local link can use to automatically configure their IPv6 addresses;
• Lifetime information for each prefix included in the advertisement;
• Sets of flags that indicate the type of autoconfiguration (stateless or statefull) that can be completed;
• Default router information (whether the router sending the advertisement should be used as a default router and, if so, the amount of time (in seconds) the router should be used as a default router);
• Additional information for hosts, such as the hop limit and MTU a host should use in packets that it originates.